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THE COSMIC CONNECTION: AN EXTRATERRESTRIAL PERSPECTIVE
Carl Sagan

For Dorion, Jeremy, and Nicholas, my sons.
May their future – and the future of all human and other beings – be bright with promise.

Dr. Carl Sagan, the author of The Cosmic Connection, is Professor of Astronomy and Space
Sciences and Director of the Laboratory for Planetary Studies at Cornell University. He received
NASA's Medal for Exceptional Scientific Achievement for his studies of Mars with Mariner 9;
he was responsible for placing the message from Earth aboard the interstellar spacecraft
Pioneer 10; and he chaired the U.S. delegation to the U.S./U.S.S.R. Conference on
Communication with Extraterrestrial Intelligence. Dr. Sagan was awarded in 1973 the Prix
Galabert – the international astronautics prize. He is editor of the planetary science journal
Icarus and is widely known for his studies of the planets, the origin of life, and the prospects
for life beyond the Earth. He is formerly of the Harvard, Caltech and Stanford Medical School
faculties.

Contents
Preface
Part One: COSMIC PERSPECTIVES
Chapter 1. A Transitional Animal
Chapter 2. The Unicorn of Cetus
Chapter 3. A Message from Earth
Chapter 4. A Message to Earth
Chapter 5. Experiments in Utopias
Chapter 6. Chauvinism
Chapter 7. Space Exploration as a Human Enterprise
I. The Scientific Interest
Chapter 8. Space Exploration as a Human Enterprise
II. The Public Interest
Chapter 9. Space Exploration as a Human Enterprise
III. The Historical Interest
Part Two: THE SOLAR SYSTEM
Chapter 10. On Teaching the First Grade
Chapter 11. "The Ancient and Legendary Gods of Old"
Chapter 12. The Venus Detective Story
Chapter 13. Venus Is Hell
Chapter 14. Science and "Intelligence"
Chapter 15. The Moons of Barsoom
Chapter 16. The Mountains of Mars
I. Observations From Earth
Chapter 17. The Mountains of Mars
II. Observations From Space
Chapter 18. The Canals of Mars
Chapter 19. The Lost Pictures of Mars
Chapter 20. The Ice Age and the Cauldron
Chapter 21. Beginnings and Ends of the Earth
Chapter 22. Terraforming the Planets
Chapter 23. The Exploration and Utilization of the Solar System
Part Three: BEYOND THE SOLAR SYSTEM
Chapter 24. Some of My Best Friends Are Dolphins

Chapter 25. "Hello, Central Casting? Send Me Twenty Extraterrestrials"
Chapter 26. The Cosmic Connection
Chapter 27. Extraterrestrial Life: An Idea Whose Time Has Come
Chapter 28. Has the Earth Been Visited?
Chapter 29. A Search Strategy for Detecting Extraterrestrial Intelligence
Chapter 30. If We Succeed
Chapter 31. Cables, Drums, and Seashells
Chapter 32. The Night Freight to the Stars
Chapter 33. Astroengineering
Chapter 34. Twenty Questions: A Classification of Cosmic Civilizations
Chapter 35. Galactic Cultural Exchanges
Chapter 36. A Passage to Elsewhen
Chapter 37. Starfolk
I. A Fable
Chapter 38. Starfolk
II. A Future
Chapter 39. Starfolk
III. The Cosmic Cheshire CatsPreface
When I was twelve, my grandfather asked me – through a translator (he had never learned
much English) – what I wanted to be when I grew up. I answered, "An astronomer," which, after
a while, was also translated. "Yes," he replied, "but how will you make a living?"
I had supposed that, like all the adult men I knew, I would be consigned to a dull, repetitive,
and uncreative job, astronomy would be done on weekends. It was not until my second year inhigh school that I discovered that some astronomers were paid to pursue their passion. I was
overwhelmed with joy; I could pursue my interest full-time.
Even today, there are moments when what I do seems to me like an improbable, if unusuallypleasant, dream: To be involved in the exploration of Venus, Mars, Jupiter, and Saturn; to try
to duplicate the steps that led to the origin of life four billion years ago on an Earth very
different from the one we know; to land instruments on Mars to search there for life; andperhaps to be engaged in a serious effort to communicate with other intelligent beings, if
such there be, out there in the dark of the night sky.
Had I been born fifty years earlier, I could have pursued none of these activities. They werethen all figments of the speculative imagination. Had I been born fifty years later, I also could
not have been involved in these efforts, except possibly the last, because fifty years from now
the preliminary reconnaissance of the Solar System, the search for life on Mars, and the studyof the origin of life will have been completed. I think myself extraordinarily fortunate to bealive at the one moment in the history of mankind when such ventures are being undertaken.
So when Jerome Agel approached me about doing a popular book to try to communicate mysense of the excitement and importance of these adventures, I was amenable – even though
his suggestion came just before the Mariner 9 mission to Mars, which I knew would occupy
most of my waking hours for many months. At a later time, after discussing communication
with extraterrestrial intelligence, Agel and I had dinner in a Polynesian restaurant in Boston. My
fortune cookie announced, "You will shortly be called upon to decipher an importantmessage." This seemed a good omen.
After centuries of muddy surmise, unfettered speculation, stodgy conservatism, andunimaginative disinterest, the subject of extraterrestrial life has finally come of age. It has now
reached a practical stage where it can be pursued by rigorous scientific techniques, where it
has achieved scientific respectability and where its significance is widely understood.
Extraterrestrial life is an idea whose time has come.
This book is divided into three major sections. In the first part I try in several ways to convey asense of cosmic perspective – living out our lives on a tiny hunk of rock and metal circling oneof 250 billion stars that make up our galaxy in a universe of billions of galaxies. The deflation

of some of our more common 7 conceits is one of the practical applications of astronomy. The
second part of the book is concerned with various aspects of our Solar System – mostly with
Earth, Mars, and Venus. Some of the results and implications of Mariner 9 can be found here.
Part Three is devoted to the possibility of communicating with extraterrestrial intelligence onplanets of other stars. Since no such contact has yet been made – our efforts to date havebeen feeble – this section is necessarily speculative. I have not hesitated to speculate within
what I perceive to be the bounds of scientific plausibility. And, although I am not by training aphilosopher or sociologist or historian, I have not hesitated to draw philosophical or social or
historical implications of astronomy and space exploration. The astronomical discoveries weare in the midst of making are of the broadest human significance. If this book plays a smallrole in broadening public consideration of these exploratory ventures, it will have served its
purpose.
As with all ongoing work and especially all speculative subjects, some of the statements inthese pages will elicit vigorous demurrers. There are other books with other opinions.
Reasoned disputation is the lifeblood of science – as is, sadly, infrequently the case in theintellectually more anemic arena of politics. But I believe that the more controversial opinions
expressed here have, nevertheless, a significant scientific constituency. I have purposely
introduced the same concept in slightly different contexts in a few places where I felt thediscussion required it. The book is carefully structured, but, for the reader who wishes tobrowse ahead, most chapters are self-contained.
There are far too many who helped shape my opinions on these subjects for me to thank them
all here. But in rereading these chapters, I find I owe a special debt to Joseph Veverka andFrank Drake, both of Cornell University, with whom over the past few years I have discussed somany aspects of this volume. The book was composed partly during a very longtranscontinental trip in a very short automobile. I thank Linda and Nicholas for theirencouragement and patience. I am also grateful to Linda for drawing two handsome humans
and one elegant unicorn. And I am grateful to the late Mauritz Escher for permission to
reproduce his "Another World" and to Robert Macintyre for the human figure and star fieldin Part Three. Jon Lomberg's paintings and drawings have been a source of intellectual andaesthetic excitement for me, and I am grateful to him for producing many of them especiallyfor this book. Hermann Eckleman's careful photographic reproductions of Lomberg's work
have facilitated their appearance in this book. And I thank Jerome Agel, without whose timeand persistence this book would never have been written.
I am indebted to John Naugle of NASA for showing me his file on public response to thePioneer 10 plaque; the Oregon System of Higher Education for permission to reproduce someideas from my book Planetary Exploration; the Forum for Contemporary History, in Santa
Barbara, for permission to reproduce a portion of my letter distributed by the Forum in
January 1973; and Cornell University Press for permission to reprint a fraction of my chapter

"The 8 Extraterrestrial and Other Hypotheses" from UFO's: A Scientific Debate, edited byCarl Sagan and Thornton Page, Cornell University Press, 1972. I am also grateful to those whohave granted me permission to reproduce in Chapter 4 their remarks on the Pioneer 10
plaque. The evolution of this book through many drafts owes much to the technical skills of Jo
Ann Cowan, and, especially, Mary Szymanski.
– Carl Sagan

Part One: COSMIC PERSPECTIVES
We shall not cease from exploration
And the end of all our exploring
Will be to arrive where we started
And know the place for the first time…
When the tongues of flame are in-folded
Into the crowned knot of fire
And the fire and the rose are one.
– T. S. Eliot, Four Quartets 10

Chapter 1: A Transitional Animal
Five billion years ago, when the Sun turned on, the Solar System was transformed
from inky blackness to a flood of light. In the inner parts of the Solar System, theearly planets were irregular collections of rock and metal – the debris, the minor
constituents of the initial cloud, the material that had not been blown away after
the Sun ignited.
These planets heated as they formed. Gases trapped in their interiors wereexuded to form atmospheres. Their surfaces melted. Volcanoes were common.
The early atmospheres were composed of the most abundant atoms and wererich in hydrogen. Sunlight, falling on the molecules of the early atmosphere,
excited them, induced molecular collisions, and produced larger molecules. Under
the inexorable laws of chemistry and physics these molecules interacted, fell into
the oceans, and further developed to produce larger molecules – molecules much
more complex than the initial atoms of which they had formed, but still
microscopic by any human standard.
These molecules, remarkably enough, are the ones of which we are made: The
building blocks of the nucleic acids, which are our hereditary material, and thebuilding blocks of the proteins, the molecular journeymen that perform the workof the cell, were produced from the atmosphere and oceans of the early Earth. We
know this because we can make these molecules today by duplicating theprimitive conditions.
Eventually, many billions of years ago, a molecule was formed that had aremarkable capability. It was able to produce, out of the molecular building blocksof the surrounding waters, a fairly accurate copy of itself. In such a molecularsystem there is a set of instructions, a molecular code, containing the sequence ofbuilding blocks from which the larger molecule is constructed. When, by accident,
there is a change in the sequence, the copy is likewise changed. Such a molecularsystem – capable of replication, mutation, and replication of its mutations – can becalled "alive." It is a collection of molecules that can evolve by natural selection.
Those molecules able to replicate faster, or to reprocess building blocks from theirsurroundings into a more useful variety, reproduced more efficiently than theircompetitors – and eventually dominated.
But conditions gradually changed. Hydrogen escaped to space. Production of
the molecular building blocks declined. The foodstuffs formerly available in greatabundance dwindled. Life was expelled from the molecular Garden of Eden. Only
those simple collections of molecules able to transform their surroundings, able toproduce efficient molecular machines for the conversion of simple into complex
molecules, were able to survive. By isolating themselves from their surroundings,
by maintaining the earlier idyllic conditions, those molecules that surroundedthemselves by membranes had an advantage. The first cells arose.
With molecular building blocks no longer available for free, organisms had towork hard to make such building blocks. Plants are the result. Plants start with air
and water, minerals and sunlight, and produce molecular building blocks of highcomplexity. Animals, such as human beings, are parasites on the plants.
Changing climate and competition among what was now a wide diversity oforganisms produced greater and greater specialization, a sophistication of function,
and an elaboration of form. A rich array of plants and animals began to cover the
Earth. Out of the initial oceans in which life arose, new environments, such as theland and the air, were colonized. Organisms now live from the top of Mount
Everest to the deepest portions of the abyssal depths. Organisms live in hot,
concentrated solutions of sulfuric acid and in dry Antarctic valleys. Organisms liveon the water adsorbed on a single crystal of salt.
Life forms developed that were finely attuned to their specific environments,
exquisitely adapted to the conditions. But the conditions changed. The organisms
were too specialized. They died. Other organisms were less well adapted, but they
were more generalized. The conditions changed, the climate varied, but theorganisms were able to continue. Many more species of organisms have diedduring the history of the Earth than are alive today. The secret of evolution is timeand death.
Among the adaptations that seem to be useful is one that we call intelligence.
Intelligence is an extension of an evolutionary tendency apparent in the simplest
organisms – the tendency toward control of the environment. The standby
biological method of control has been the hereditary material: Information passed
on by nucleic acids from generation to generation – information on how to build anest; information on the fear of falling, or of snakes, or of the dark; information on
how to fly south for the winter. But intelligence requires information of an
adaptive quality developed during the lifetime of a single individual. A variety oforganisms on the Earth today have this quality we call intelligence: The dolphinshave it, and so do the great apes. But it is most evident in the organism called Man.
In Man, not only is adaptive information acquired in the lifetime of a single
individual, but it is passed on extra-genetically through learning, through books,
through education. It is this, more than anything else, that has raised Man to his
present pre-eminent status on the planet Earth.

We are the product of 4.5 billion years of fortuitous, slow, biological evolution.
There is no reason to think that the evolutionary process has stopped. Man is atransitional animal. He is not the climax of creation.
The Earth and the Sun have life expectancies of many more billions of years.
The future development of man will likely be a cooperative arrangement among
controlled biological evolution, genetic engineering, and an intimate partnership
between organisms and intelligent machines. But no one is in a position to makeaccurate predictions of this future evolution. All that is clear is that we cannot
remain static.
In our earliest history, so far as we can tell, individuals held an allegiancetoward their immediate tribal group, which may have numbered no more than ten
or twenty individuals, all of whom were related by consanguinity. As time wenton, the need for cooperative behavior – in the hunting of large animals or large
herds, in agriculture, and in the development of cities – forced human beings intolarger and larger groups. The group that was identified with, the tribal unit,
enlarged at each stage of this evolution. Today, a particular instant in the 4.5billion-year history of Earth and in the several-million-year history of mankind,most human beings owe their primary allegiance to the nation-state (althoughsome of the most dangerous political problems still arise from tribal conflicts
involving smaller population units).
Many visionary leaders have imagined a time when the allegiance of anindividual human being is not to his particular nation-state, religion, race, or
economic group, but to mankind as a whole; when the benefit to a human beingof another sex, race, religion, or political persuasion ten thousand miles away is asprecious to us as to our neighbor or our brother. The trend is in this direction, but
it is agonizingly slow. There is a serious question whether such a global selfidentification of mankind can be achieved before we destroy ourselves with thetechnological forces our intelligence has unleashed.
In a very real sense human beings are machines constructed by the nucleic
acids to arrange for the efficient replication of more nucleic acids. In a sense ourstrongest urges, noblest enterprises, most compelling necessities, and apparent free
wills are all an expression of the information coded in the genetic material: We
are, in a way, temporary ambulatory repositories for our nucleic acids. This does
not deny our humanity; it does not prevent us from pursuing the good, the true,
and the beautiful. But it would be a great mistake to ignore where we have comefrom in our attempt to determine where we are going.

There is no doubt that our instinctual apparatus has changed little from thehunter-gatherer days of several hundred thousand years ago. Our society haschanged enormously from those times, and the greatest problems of survival in thecontemporary world can be understood in terms of this conflict – between what
we feel we must do because of our primeval instincts and what we know we must
do because of our extragenetic learning.
If we survive these perilous times, it is clear that even an identification with allof mankind is not the ultimate desirable identification. If we have a profoundrespect for other human beings as co-equal recipients of this precious patrimonyof 4.5 billion years of evolution, why should the identification not apply also to all
the other organisms on Earth, which are equally the product of 4.5 billion years of
evolution? We care for a small fraction of the organisms on Earth – dogs, cats, andcows, for example – because they are useful or because they flatter us. But spiders
and salamanders, salmon and sunflowers are equally our brothers and sisters.
I believe that the difficulty we all experience in extending our identification
horizons in this way is itself genetic. Ants of one tribe will fight to the death
intrusions by ants of another. Human history is filled with monstrous cases ofsmall differences – in skin pigmentation, or abstruse theological speculation, or
manner of dress and hair style – being the cause of harassment, enslavement, andmurder.
A being quite like us, but with a small physiological difference – a third eye,say, or blue hair covering the nose and forehead – somehow evokes feelings ofrevulsion. Such feelings may have had adaptive value at one time in defending oursmall tribe against the beasts and neighbors. But in our times, such feelings are
obsolete and dangerous.
The time has come for a respect, a reverence, not just for all human beings, but
for all life forms – as we would have respect for a masterpiece of sculpture or an
exquisitely tooled machine. This, of course, does not mean that we should
abandon the imperatives for our own survival. Respect for the tetanus bacillus
does not extend to volunteering our body as a culture medium. But at the sametime we can recall that here is an organism with a biochemistry that tracks backdeep into our planet's past. The tetanus bacillus is poisoned by molecular oxygen,
which we breathe so freely. The tetanus bacillus, but not we, would be at home in
the hydrogen-rich, oxygen-free atmosphere of primitive Earth.
A reverence for all life is implemented in a few of the religions of the planet
Earth – for example, among the Jains of India. And something like this idea is
responsible for vegetarianism, at least in the minds of many practitioners of thisdietary constraint. But why is it better to kill plants than animals?
Human beings can survive only by killing other organisms. But we can makeecological compensation by also growing other organisms; by encouraging theforest; by preventing the wholesale slaughter of organisms such as seals andwhales, imagined to have industrial or commercial value; by outlawing gratuitous
hunting, and by making the environment of Earth more livable – for all its
inhabitants.
There may be a time, as I describe in Part III of this book, when contact will bemade with another intelligence on a planet of some far-distant star, beings withbillions of years of quite independent evolution, beings with no prospect oflooking very much like us – although they may think very much like us. It is
important that we extend our identification horizons, not just down to thesimplest and most humble forms of life on our own planet, but also up to theexotic and advanced forms of life that may inhabit, with us, our vast galaxy ofstars.

Chapter 2: The Unicorn of Cetus
In the night sky, when the air is clear, there is a cosmic Rorschach test awaiting us.
Thousands of stars, bright and faint, near and far, in a glittering variety of colors,
are peppered across the canopy of night. The eye, irritated by randomness, seeking
order, tends to organize into patterns these separate and distinct points of light.
Our ancestors of thousands of years ago, who spent almost all their time out ofdoors in a pollution-free atmosphere, studied these patterns carefully. A richmythological lore evolved.
Much of the original substance of this stellar mythology has not come down tous. It is so ancient, has been retold so many times, and especially in the past few
thousand years by individuals unfamiliar with the appearance of the sky, thatmuch has been lost. Here and there, in odd places, there remain some echoes of
cosmic stories about patterns in the sky.
In the Book of Judges there is an account of a slain lion discovered to beinfested by a hive of bees, a strange and apparently pointless incident. But theconstellation of Leo in the night sky is adjacent to a cluster of stars, visible on aclear night as a fuzzy patch of light, called Praesepe. From its telescopic
appearance, modern astronomers call it "The Beehive." I wonder if an image of
Praesepe, obtained by one man of exceptional eyesight, in days before thetelescope, has been preserved for us in the Book of Judges.
When I look out into the night sky, I cannot discern the outline of a lion in theconstellation Leo. I can make out the Big Dipper, and, if the night is clear, theLittle Dipper. I am at a loss to make out much of a hunter in Orion or a fish in theconstellation of Pisces, to say nothing of a charioteer in Auriga. The mythicalbeasts, personages, and instruments placed by men in the sky are arbitrary, notobvious. There are agreements about which constellation is which – sanctioned inrecent years by the International Astronomical Union, which draws boundaries
separating one constellation from another. But there are few clear pictures in thesky.
These constellations, while drawn in two dimensions, are fundamentally inthree dimensions. A constellation, such as Orion, is composed of bright stars at
considerable distances from Earth and dim stars much closer. Were we to change
our perspective, move our point of view – with, for example, an interstellar spacevehicle – the appearance of the sky would change. The constellations would
slowly distort.

Largely through the efforts of David Wallace at the Laboratory for Planetary
Studies at Cornell University, an electronic computer has been programmed with
the information on the three-dimensional positions from the Earth to each of thebrightest and nearest stars – down to about fifth magnitude, the limiting brightness
visible to the naked eye on a clear night. When we ask the computer to show us
the appearance of the sky from Earth, we see results of the sort displayed in theaccompanying figures: One for the northern circumpolar constellations, including
the Big Dipper, the Little Dipper, and Cassiopeia; one for the southern
circumpolar constellations, including the Southern Cross; and one for the broad
range of stars at middle celestial latitudes, including Orion and the constellations of
the zodiac. If you are not a student of the conventional constellations, you will, I
believe, have some difficulty making out scorpions or virgins in the picture.
We now ask the computer to draw us the sky from the nearest star to ourown, Alpha Centauri, a triple-star system, about 4.3 light-years from Earth. In
terms of the scale of our Milky Way Galaxy, this is such a short distance that ourperspectives remain almost exactly the same. From α Cen the Big Dipper appears
just as it does from Earth. Almost all the other constellations are similarly
unchanged. There is one striking exception, however, and that is the constellation
Cassiopeia. Cassiopeia, the queen of an ancient kingdom, mother of Andromeda
and mother-in-law of Perseus, is mainly a set of five stars arranged as a W or an M,
depending on which way the sky has turned. From Alpha Centauri, however,there is one extra jog in the M; a sixth star appears in Cassiopeia, one significantly
brighter than the other five. That star is the Sun. From the vantage point of thenearest star, our Sun is a relatively bright but unprepossessing point in the nightsky. There is no way to tell by looking at Cassiopeia from the sky of a hypotheticalplanet of Alpha Centauri that there are planets going around the Sun, that on thethird of these planets there are life forms, and that one of these life forms
considers itself to be of quite considerable intelligence. If this is the case for thesixth star in Cassiopeia, might it not also be the case for innumerable millions ofother stars in the night sky?
One of the two stars that Project Ozma examined a decade ago for possible
extraterrestrial intelligent signals was Tau Ceti, in the constellation (as seen from
Earth) of Cetus, the whale. In the accompanying figure, the computer has drawn
the sky as seen from a hypothetical planet of T Cet. We are now a little more thaneleven light-years away from the Sun. The perspective has changed somewhat
more. The relative orientation of the stars has varied, and we are free to invent
new constellations – a psychological projective test for the Cetians.
I asked my wife, Linda, who is an artist, to draw a constellation of a unicorn inthe Cetian sky. There is already a unicorn in our sky, called Monoceros, but I
wanted this to be a larger and more elegant unicorn – and also one slightly
different from common terrestrial unicorns – with six legs, say, rather than four.
She invented quite a handsome beast. Contrary to my expectation that he would
have three pairs of legs, he is quite proudly galloping on two clusters of three legs
each, one fore and one aft. It seems quite a believable gallop. There is a tiny starthat is just barely seen at the point where the unicorn's tail joins the rest of his
body. That faint and un-inspiringly positioned star is the Sun. The Cetians may
consider it an amusing speculation that a race of intelligent beings lives on a planet
circling the star that joins the unicorn to his tail.
When we move to greater distances from the Sun than Tau Ceti – to forty or
fifty light-years – the Sun dwindles still further in brightness until it is invisible toan unaided human eye. Long interstellar voyages – if they are ever undertaken –will not use dead-reckoning on the Sun. Our mighty star, on which all life on Earthdepends, our Sun, which is so bright that we risk blindness by prolonged direct
viewing, cannot be seen at all at a distance of a few dozen light-years – athousandth of the distance to the center of our Galaxy.

Chapter 3: A Message from Earth
Mankind's first serious attempt to communicate with extraterrestrial civilizations
occurred on March 3, 1972, with the launching of the Pioneer 10 spacecraft from
Cape Kennedy. Pioneer 10 was the first space vehicle designed to explore theenvironment of the planet Jupiter and, earlier in its voyage, the asteroids that lie
between the orbits of Mars and Jupiter. Its orbit was not disturbed by an errant
asteroid – the safety factor was estimated as 20 to 1. It approached Jupiter on
December 3, 1973, and then was accelerated by Jupiter's gravity to become thefirst man-made object to leave the Solar System. Its exit velocity is about 7 miles
per second.
Pioneer 10 is the speediest object launched to date by mankind. But space isvery empty, and the distances between the stars are vast. In the next 10 billion
years, Pioneer 10 will not enter the planetary system of any other star, evenassuming that all the stars in the Galaxy have such planetary systems. The
spacecraft will take about 80,000 years merely to travel the distance to the nearest
star, about 4.3 light-years away.
But Pioneer 10 is not directed to the vicinity of the nearest star. Instead, it willbe traveling toward a point on the celestial sphere near the boundary of theconstellations Taurus and Orion, where there are no nearby objects.
It is conceivable that the spacecraft will be encountered by an extraterrestrial
civilization only if such a civilization has an extensive capability for interstellar
space flight and is able to intercept and recover such silent space derelicts.
Placing a message aboard Pioneer 10 is very much like a shipwrecked sailor
casting a bottled message into the ocean – but the ocean of space is much vasterthan any ocean on Earth.
When my attention was drawn to the possibility of placing a message in aspace-age bottle, I contacted the Pioneer 10 project office and NASA headquarters
to see if there were any likelihood of implementing this suggestion. To my surpriseand delight, the idea met with approval at all steps up the NASA hierarchy,
despite the fact that it was – by ordinary standards – very late to make even tinychanges in the spacecraft. During a meeting of the American Astronomical Society
in San Juan, Puerto Rico, in December 1971, I discussed privately various possible
messages with my colleague Professor Frank Drake, also of Cornell. In a few hours
we decided tentatively on the contents of the message. The human figures wereadded by my artist wife, Linda Salzman Sagan. We do not think it is the optimum
conceivable message for such a purpose: There were a total of only three weeks
for the presentation of the idea, the design of the message, its approval by NASA,and the engraving of the final plaque. An identical plaque has been launched in1973 on the Pioneer 11 spacecraft, on a similar mission.
On the title page of this chapter is shown the message. It is etched on a 6-inchby 9-inch gold-anodized aluminum plate, attached to the antenna support struts ofPioneer 10. The expected erosion rate in interstellar space is sufficiently small that
this message should remain intact for hundreds of millions of years, and probably
for a much longer period of time. It is, thus, the artifact of mankind with thelongest expected lifetime.
The message itself intends to communicate the locale, epoch, and something of
the nature of the builders of the spacecraft. It is written in the only language weshare with the recipients: Science. At top left is a schematic representation of thehyperfine transition between parallel and antiparallel proton and electron spins of
the neutral hydrogen atom. Beneath this representation is the binary number 1.
Such transitions of hydrogen are accompanied by the emission of a radiofrequency photon of wavelength about 21 centimeters and frequency of about
1,420 Megahertz. Thus, there is a characteristic distance and a characteristic timeassociated with the transition. Since hydrogen is the most abundant atom in the
Galaxy, and physics is the same throughout the Galaxy, we think there will be no
difficulty for an advanced civilization to understand this part of the message. But
as a check, on the right margin is the binary number 8 (1---) between two tote
marks, indicating the height of the Pioneer 10 spacecraft, schematically represented
behind the man and the woman. A civilization that acquires the plaque will, ofcourse, also acquire the spacecraft, and will be able to determine that the distanceindicated is indeed close to 8 times 21 centimeters, thus confirming that thesymbol at top left represents the hydrogen hyperfine transition.
Further binary numbers are shown in the radial pattern comprising the mainpart of the diagram at left center. These numbers, if written in decimal notation,
would be ten digits long. They must represent either distances or times. If
distances, they are of the order of several times 1011 centimeters, or a few dozen
times the distance between the Earth and the Moon. It is highly unlikely that wewould consider them useful to communicate. Because of the motion of objects
within the Solar System, such distances vary in continuous and complex ways.
However, the corresponding times are on the order of 1/10 second to 1 second.
These are the characteristic periods of the pulsars, natural and regular sources of
cosmic radio emission; pulsars are rapidly rotating neutron stars produced incatastrophic stellar explosions (see Chapter 38). We believe that a scientificallysophisticated civilization will have no difficulty understanding the radial burst
pattern as the positions and periods of 14 pulsars with respect to the Solar System

of launch.
But pulsars are cosmic clocks that are running down at largely known rates.
The recipients of the message must ask themselves not only where it was everpossible to see 14 pulsars arrayed in such a relative position, but also when it waspossible to see them. The answers are: Only from a very small volume of the
Milky Way Galaxy and in a single year in the history of the Galaxy. Within that
small volume there are perhaps a thousand stars; only one is anticipated to havethe array of planets with relative distances as indicated at the bottom of the
diagram. The rough sizes of the planets and the rings of Saturn are also
schematically shown. A schematic representation of the initial trajectory of thespacecraft launched from Earth and passing by Jupiter is also displayed. Thus, themessage specifies one star in about 250 billion and one year (1970) in about 10
billion.
The content of the message to this point should be clear to an advanced
extraterrestrial civilization, which will, of course, have the entire Pioneer 10
spacecraft to examine as well. The message is probably less clear to the man on
the street, if the street is on the planet Earth. (However, scientific communities on
Earth have had little difficulty decoding the message.) The opposite is the casewith the representations of human beings to the right. Extraterrestrial beings,
which are the product of 4.5 billion years or more of independent biologicalevolution, may not at all resemble humans, nor may the perspective and linedrawing conventions be the same there as here. The human beings are the mostmysterious part of the message.

Chapter 4: A Message to Earth

The golden greeting card placed aboard the Pioneer 10 spacecraft was intended forthe remote contingency that representatives of an advanced extraterrestrial
civilization, some time in the distant future, might encounter this first artifact ofmankind to leave the Solar System. But the message has had a more immediate
impact. It has already been meticulously studied – not by extraterrestrials, but byterrestrials. Human beings all over the planet Earth have examined the message,
applauded it, criticized it, interpreted it, and proposed alternative messages.
The graphics of the message have been reproduced widely in newspapers andtelevision programs, small art and literary magazines, and national newsweeklies.
We have received letters from scientists and housewives, historians and artists,
feminists and homosexuals, military and foreign service officers, and one professor

of bass fiddle. Our plaque has been reproduced for commercial sale by anengraving company, a distributor of scientific knickknacks, a manufacturer oftapestry, and an Italian mint specializing in silver ingots – all, incidentally, withoutauthorization.
The great majority of comments have been favorable, some extraordinarily
enthusiastic. The large street advertising billboards for the Tribune of Geneva,
Switzerland, announced "Message de la NASA pour les extraterrestres!" Onescientist writes to say that the description of the scientific basis of the plaque wepublished in the American journal Science was the first scientific paper he had
ever read that moved him to tears of joy. A correspondent in Athens, Georgia,
writes, "We'll all be gone before this particular message in a bottle is picked up bysome indescribable spacecomber; nevertheless, its very existence, the audacity ofthe dream, inevitably produces in me – and many others I know – the feelings of a
Balboa, a Leeuwenhoek, a human being being human!"At the California Institute of Technology, where the graffiti is arcane, some
unknown artist drew the message life-size on a barrier at a building site, eliciting
friendly greetings from the inhabitants, which we hope will serve as a model for
extraterrestrial readers (see the illustration on the facing page).
But there were also critical comments. They were not directed at the pulsar
map, which was the scientific heart of the message, but rather at the
representation of the man and the woman. The original drawings of this couple
were made by my wife and were based upon the classical models of Greek
sculpture and the drawings of Leonardo da Vinci. We do not think this man andwoman are ignoring each other. They are not shown holding hands lest theextraterrestrial recipients believe that the couple is one organism joined at thefingertips. (In the absence of indigenous horses, both the Aztecs and the Incasinterpreted the mounted conquistador as one animal – a kind of two-headed
centaur.) The man and woman are not shown in precisely the same position or
carriage so that the suppleness of the limbs could be communicated – although wewell understand that the conventions of perspective and line drawing popular on
Earth may not be readily apparent to civilizations with other artistic conventions.
The man's right hand is raised in what I once read in an anthropology book is a
"universal" sign of good will – although any literal universality is of course unlikely.
At least the greeting displays our opposable thumbs. Only one of the two people
is shown with hand raised in greeting, lest the recipients deduce erroneously that
one of our arms is bent permanently at the elbow.
Several women correspondents complain that the woman appears too passive.

One writes that she also wishes to greet the universe, with both arms outstretchedin womanly salutation. The principal feminine criticism is that the woman isdrawn incomplete – that is, without any hint of external genitalia. The decision toomit a very short line in this diagram was made partly because conventional
representation in Greek statuary omits it. But there was another reason: Our desire
to see the message successfully launched on Pioneer 10. In retrospect, we may havejudged NASA's scientific-political hierarchy as more puritanical than it is. In the
many discussions that I held with such officials, up to the Administrator of the
National Aeronautics and Space Administration and the President's Science
Adviser, not one Victorian demurrer was ever voiced; and a great deal of helpful
encouragement was given.
Yet it is clear that at least some individuals were offended even by the existing
representation. The Chicago Sun Times, for example, published three versions of
the plaque in different editions all on the same day: In the first the man was
represented whole; in the second, suffering from an awkward and botchedairbrush castration; and in the final version – intended no doubt to reassure thefamily man dashing home – with no sexual apparatus at all. This may have pleased
one feminist correspondent who wrote to the New York Times that she was soenraged at the incomplete representation of the woman that she had an irresistible
urge "to cut off the man's … right arm!"
The Philadelphia Inquirer published on its front page an illustration of theplaque, but with the nipples of the woman and the genitalia of the man removed.
The assistant managing editor was quoted as saying, "A family newspaper must
uphold community standards."
An entire mythology has evolved about the absence of discernible female
genitalia. It was a column by the respected science writer Tom O'Toole, of the
Washington Post, that first reported that NASA officials had censored an original
depiction of the woman. This tale was then circulated in nationally syndicatedcolumns by Art Hoppe, Jack Stapleton, Jr., and others. Stapleton imagined theenraged citizens of another planet receiving the plaque, and in a paroxysm of
moral outrage covering over with adhesive tape the pornographic representationof the feet of the man and the woman. One letter writer to the Washington Daily
News proposed that if the woman was to be censored, then for consistency thenoses of the humans should have been painted blue. A tut-tutting letter in Playboy
magazine complained about this further intrusion of government censorship,
already quite bad enough, into the lives of the citizenry. Editorials in sciencefiction magazines also took the government to task. The idea of government
censorship of the Pioneer 10 plaque is now so well documented and firmlyentrenched that no statement from the designers of the plaque to the contrary canplay any role in influencing the prevailing opinion. But we can at least try.
What sexuality there is in the message also drew epistolary fire. The Los
Angeles Times published a letter from an irate reader that went:
I must say I was shocked by the blatant display of both male and female sexorgans on the front page of the Times. Surely this type of sexual exploitation
is below the standards our community has come to expect from the Times.
Isn't it enough that we must tolerate the bombardment of pornography
through the media of film and smut magazines? Isn't it bad enough that ourown space agency officials have found it necessary to spread this filth evenbeyond our own solar system?
This was followed several days later by another letter in the Times:
I certainly agree with those people who are protesting our sending thosedirty pictures of naked people out into space. I think the way it should havebeen done would have been to visually bleep out the reproductive organs of
the drawings of the man and the woman. Next to them should have been apicture of a stork carrying a little bundle from heaven.
Then if we really want our celestial neighbors to know how far we haveprogressed intellectually, we should have included pictures of Santa Claus,
the Easter Bunny, and the Tooth Fairy.
The New York Daily News headlined the story in typical fashion: "Nudes and
Map tell about Earth to Other Worlds."
Some correspondents argue that the function of the sexual organs would not be
obvious even had they been graphically displayed, and urged on us a sequence of
cartoons from copulation to birth to puberty to copulation. There was not quite
room for this on a 6-inch by 9-inch plaque. I can also imagine the letters thatwould then have been written to the Los Angeles Times.
An article in Catholic Review criticizes the plaque because it "includes
everything but God," and suggests that, rather than a pair of human beings, itwould have been better to have borne a sketch of a pair of praying hands.
Another correspondent maintains that the perspective conventions are
insuperably difficult, and urges us to send the complete cadavers of a man and awoman. They would be perfectly preserved in the cold of space, and could be
examined by extraterrestrials in detail. We declined on grounds of excess weight.
The front page of the Berkeley, California, Barb, apparently intending toconvey an impression that the man and woman on the message were too straight,reproduced them with the caption, "Hello. We're from Orange County."
This comment touches on an aspect of the representation of the man andwoman that I personally feel much worse about, although it has received almost
no other public notice. In the original sketches from which the engravings were
made, we made a conscious attempt to have the man and woman panracial. The
woman was given epicanthian folds and in other ways a partially Asian
appearance. The man was given a broad nose, thick lips, and a short "Afro" haircut.
Caucasian features were also present in both. We had hoped to represent at least
three of the major races of mankind. The epicanthian folds, the lips, and the nose
have survived into the final engraving. But because the woman's hair is drawn only
in outline, it appears to many viewers as blond, thereby destroying the possibilityof a significant contribution from an Asian gene pool. Also, somewhere in thetranscription from the original sketch drawing to the final engraving the Afro wastransmuted into a very non-African Mediterranean-curly haircut. Nevertheless, theman and woman on the plaque are, to a significant degree, representative of thesexes and races of mankind.
Professor E. Gombrich, the Director of the Warburg Institute, a leading art
school in London, criticizes the plaque in the journal Scientific American. He
wonders how the plaque can possibly be expected to be visible to an
extraterrestrial organism that may not have developed the sense of sight at visible
wavelengths. The answer is derived simply from the laws of physics. Planetaryatmospheres absorb light from the nearby sun or suns because of three molecular
processes. The first is a change in the energy state of individual electrons attached
to atoms. These transitions occur in the ultraviolet, X-ray, and gamma-ray parts ofthe spectrum and tend to make a planetary atmosphere opaque at thesewavelengths. Second, there are vibrational transitions that occur when two atoms
in a given molecule oscillate with respect to each other. Such transitions tend to
make planetary atmospheres opaque in the near infrared part of the spectrum.
Third, molecules undergo rotational transitions, due to the free rotation of themolecule. Such transitions tend to absorb in the far infrared. As a result, quite
generally, the radiation from the nearby star, which penetrates through a planetaryatmosphere, will be in the visible and in the radio parts of the spectrum – theparts that are not absorbed by the atmosphere.
In fact, these are the principal "windows" that astronomers use for surveying
the universe from the Earth's surface. But radio wavelengths are so long that noorganisms of reasonable size can develop pictures of their surroundings with radio
wavelength "eyes." Therefore, we expect optical frequency sensors to be
developed quite widely among organisms on planets of stars throughout theGalaxy.
However, even if we imagine organisms whose eyes work in the infrared region(or, for that matter, in the gamma-ray region) and who are able to intercept
Pioneer 10 in interstellar space, it is probably not asking too much of them to havecontrivances that scan the plaque at frequencies to which their eyes are insensitive.
Because the engraved lines on the plaque are darker than the surrounding goldanodized aluminum, the message should be entirely visible even in the infrared.
Gombritch also takes us to task for portraying an arrow as a sign of thespacecraft's trajectory. He maintains that arrows would be understandable only tocivilizations that have evolved, as ours has, from a hunting society. But here again
it does not take a very intelligent extraterrestrial to understand the meaning of thearrow. There is a line that begins on the third planet of a solar system and ends,
somewhere in interstellar space, at a schematic representation of the spacecraft –which the discoverers of the message have at "hand": The plaque is attached to thespacecraft. From this I would hope they would be able to argue backward to ourhunter-gatherer ancestors.
In the same way, the relative distances of the planets from the Sun, shown bybinary notation at the bottom of the plaque, indicate that we use base-10
arithmetic. From the fact that we have 10 fingers and 10 toes – drawn with somecare on the plaque – I hope any extraterrestrial recipients will be able to deducethat we use base-10 arithmetic and that some of us count on our fingers. From thestumpiness of our toes they may even be able to deduce that we evolved fromarboreal ancestors.
There are other respects in which the message has proved to be a psychologicalprojective test. One man writes of his concern that the message has doomed all of
mankind. American movies of Second World War vintage, he argues, are very
likely propagating via television transmission through interstellar space. From suchprogramming, the extraterrestrials will easily be able to deduce (1) that the Nazis
were very bad fellows, and (2) that they greeted each other with their right handextended outward. From the fact that the man on the plaque is portrayed as
making what our correspondent erroneously perceives as the same sort of greeting,
he is concerned that the extraterrestrials will deduce that the wrong side won
World War II and promptly mount a punitive expedition to Earth to set mattersstraight.
Such a letter more nearly describes the state of mind of the writer than of thelikely extraterrestrial recipients of the message. The raised right hand in greeting ishistorically connected with militarism, but in a negative way: The raised andempty right hand symbolizes that no weapon is being carried.
For me, some of the most moving responses to the message are the works ofart and poetry that it evoked. Mr. 'Aim Morhardt is a painter of water colors ofthe desert and sierras who lives in Bishop, California, where, perhaps notcoincidentally, the giant Goldstone tracking station, which commands Pioneer 10, is
located. Mr. Morhardt's poem follows:
Pioneer 10: The Golden Messenger.
The dragon prows that cruised the northern seas,
Questing adventure with the fighting clan;
The gallant mermaid bows blown down the breeze
On barquentine and slim-hulled merchantman;
All the discoverers of unknown lands
Gone in this winged age where naught remains
Of new strange treasure on some foreign strand,
So well-known earth, such charted routes and lanes.
Now the new figurehead of man appears,
Facing the vast immeasurable unknown,
Naked, star-sped, beyond the call of years,
Hand in hand, outward bound, and so alone.
Go, tiny messenger of our your race,
Touch, if you can, harbor in some far place.
Mr. Arvid F. Sponberg, of Belfast, Northern Ireland, writes: "The voyage ofPioneer 10 – and the voyages of those like her – will have an effect that poets,
painters and musicians will not long ignore. The existence of the idea of Pioneer 10
is proof of this. The scientific mission of course is of incalculable value andinterest, but the idea of the journey is of even greater imaginative value. Pioneer 10
brings closer the day when artists must confront man's new voyage as experienceand not fantasy."
Mr. Sponberg composed for us a poem in sonnet form:
New Odyssey
Away, afar, beyond, bereft of kin,
Wayward, wandering, far ranging vagabonds,
Yearning, stardrawn, the Pioneers sweep on,
Outward bound, adrift on the solar wind.
A man, a woman, orphans of warm earth
Or splendid voyageurs with golden sails,
Or gypsies roaming ancient stellar trails,

A caravan in quest of celestial berth.
If, deep within cold interstellar space,
Some fearful eye spies life on this raft,
Will it perceive the heart within our craft,
A pulsar pounding out the rhythms of peace?
A spirit's starburst pierces new frontiers;
An Odyssey is our home; let us praise Pioneers!
There is, of course, the possibility that the message on Pioneer 10 – invented byhuman beings but directed at creatures of a very different kind – may prove
ultimately mysterious to them. We think not. We think we have written themessage – except for the man and woman – in a universal language. The
extraterrestrials cannot possibly understand English or Russian or Chinese or
Esperanto, but they must share with us common mathematics and physics andastronomy. I believe that they will understand, with no very great effort, thismessage written in the galactic language: "Scientific."
But we may be wrong. One exploration of a total misunderstanding – and by
far the most amusing such description – was made by the British humor magazine
Punch in an article headlined, "According to the [Paris] Herald Tribune only one inten of NASA scientists was able to figure out its message. So what chance havethe aliens got?" Punch presents an opinion sampling of four representative
extraterrestrials. They should be read with close reference to the illustration of theactual message:"Still, I must emphasise that we are only guessing at this stage and none of us
has been able to explain the significance of the dots along the bottom. A
suggestion that it could be a map of some metropolitan railway has been made tous, but we feel that this fails to take into account the arrowed position of a
capsized yacht, or possibly a garden trowel. The inclusion of a naked blonde makes
it more than likely, however, that this is some kind of a joke sent out by abackward planet, possibly that being used by the Earthlings.""Speaking as a fourteen-legged and extremely thin spider," said a voice fromthe back of Andromeda 9, "I have studied this post-card from the Earthlings and I
take it as a snub. The caricature of our species is both crude and inept, suggesting,amongst other things, that we've got a right leg longer than all the rest.
Furthermore, the geometric being which is standing at the back has clearly turned
its back on us and one of the other two is pointing five antennae in a frankly
sordid gesture. There seems little reason to doubt, amongst us intelligent spiders,that this thing is intended as a declaration of war. The illustrated talent for thecreature on the right to be capable of firing arrows from the shoulder is aparticularly sinister turn and one that bodes badly for a long and bitter struggle
with the Earthlings.""Whatever it is," the Being declared, "it's not come all this way for nothing. My
guess is that it's trying to tell us something. Just suppose, for argument's sake, that
this thing which we have before us is not an actual creature itself but an artifact ofsome sort. Such a theory might explain for a start why it hasn't so far uttered inany way. No, this thing was sent – probably from some primitive threedimensional world – and I say it's meant to be a picture or a cipher with a message
for us Beings. What the message is, of course, depends on which way up it's
supposed to be. I shouldn't be a bit surprised if it was rude.""Magnificent!" The thing on Alpha Centaurus was overcome with awe. "Truly
magnificent! As far as is known, this is the first time ever that has fetched up on
our planet an original work by the erstwhile Earthling Leonardo da Vinci! Our
telescopes show that the style is unmistakably his. Nevertheless, the discovery isbound to alter some of the intelligence data on the Earth. It was not known, until
now, that the climate was sufficiently warm for policemen to go to point duty
without clothes in their world nor that key limbs on the Earthlings are apparently
operated by string. Let us hope they send us further simple greeting-cards soon."
Perhaps the most perceptive editorial comment is the New York Times':… that gold-plated plaque is more of a challenge to us. Despite the uncanny
mastery of celestial laws that permits man to shoot his artifacts at the stars,
we find ourselves still depressingly inept at ordering our own systems hereon Earth. Even as we try to find a way to insure that sapient man will notconsume his planet in nuclear fires, a rising chorus warns us that man mayvery well exhaust his earth either by overbreeding or by inordinate demands
on its resources, or both.
So the marker launched into space is at the same time a gauntlet thrown
down to earth: That the gold-plated plaque convey in its time the message
that man is still here – not that he had been here.
The message aboard Pioneer 10 has been good fun. But it has been more thanthat. It is a kind of cosmic Rorschach test, in which many people see reflected
their hopes and fears, their aspirations and defeats – the darkest and the mostluminous aspects of the human spirit.
The sending of such a message forces us to consider how we wish to be
represented in a cosmic discourse. What is the image of mankind that we mightwish to represent to a superior civilization elsewhere in the Galaxy? The
transmittal of the Pioneer 10 message encourages us to consider ourselves in cosmic
perspective.
The greater significance of the Pioneer 10 plaque is not as a message to out
there; it is as a message to back here.

Chapter 5: Experiments in Utopias
In assessing the likelihood of advanced technical civilizations elsewhere in the
Galaxy, the most important fact is the one about which we know least – thelifetime of such a civilization. If civilizations destroy themselves rapidly after
reaching the technological phase, at any given moment (like now) there may bevery few of them for us to contact. If, on the other hand, a small fraction ofcivilizations learn to live with weapons of mass destruction and avoid both naturaland self-generated catastrophes, the number of civilizations for us to communicate
with at any given moment may be very large.
This assessment is one reason we are concerned about the lifetime of such
civilizations. There is a more pressing reason, of course. For personal reasons, wehope that the lifetime of our own civilization will be long.
There is probably no epoch in the history of mankind that has undergone somuch and so many varieties of change as the present time. Two hundred years ago,
information could be sent from one city to another no faster than by horse. Today,
the information can be sent via telephone, telegraph, radio, or television at thevelocity of light. In two hundred years the speed of communication has increased
by a factor of thirty million. We believe there will be no corresponding futureadvance, since messages cannot, we believe, be sent faster than the velocity oflight.
Two hundred years ago it took as long to go from Liverpool to London as it
now does from the Earth to the Moon. Similar changes have occurred in theenergy resources available to our civilization, in the amount of information that isstored and processed, in methods of food production and distribution, in thesynthesis of new materials, in the concentration of population from thecountryside to the cities, in the vast increase in population, in improved medical
practice, and in enormous social upheaval.
Our instincts and emotions are those of our hunter-gatherer ancestors of amillion years ago. But our society is astonishingly different from that of a million
years ago. In times of slow change, the insights and skills learned by one generation
are useful, tried, and adaptive, and are gladly received when passed down to thenext generation. But in times like today, when the society changes significantly inless than a human lifetime, the parental insights no longer have unquestioned
validity for the young. The so-called generation gap is a consequence of the rate ofsocial and technological change.

Even within a human lifetime, the change is so great that many people arealienated from their own society. Margaret Mead has described older people today
as involuntary immigrants from the past to the present.
Old economic assumptions, old methods of determining political leaders, old
methods of distributing resources, old methods of communicating informationfrom the government to the people – and vice versa – all of these may once havebeen valid or useful or at least somewhat adaptive, but today may no longer havesurvival value at all. Old oppressive and chauvinistic attitudes among the races,
between the sexes, and between economic groups are being justifiably challenged.
The fabric of society throughout the world is ripping.
At the same time, there are vested interests opposed to change. These include
individuals in power who have much to gain in the short run by maintaining theold ways, even if their children have much to lose in the long run. They are
individuals who are unable in middle years to change the attitudes inculcated intheir youth.
The situation is a very difficult one. The rate of change cannot continue
indefinitely; as the example of the rate of communication indicates, limits must be
reached. We cannot communicate faster than the velocity of light. We cannot
have a population larger than Earth's resources and economic distribution facilities
can maintain. Whatever the solutions to be achieved, hundreds of years from now
the Earth is unlikely still to be experiencing great social stress and change. We will
have reached some solution to our present problems. The question is, which
solution?
In science a situation as complicated as this is difficult to treat theoretically.
We do not understand all the factors that influence our society and, therefore,cannot make reliable predictions on what changes are desirable. There are too
many complex interactions. Ecology has been called the subversive science
because every time a serious effort to preserve a feature of the environment ismade, it runs into enormous numbers of social or economic vested interests. The
same is true every time we attempt to make a major change in anything that iswrong; the change runs through society as a whole. It is difficult to isolate small
fragments of the society and change them without having profound influences on
the rest of society.
When theory is not adequate in science, the only realistic approach isexperimental. Experiment is the touchstone of science on which the theories areframed. It is the court of last resort. What is clearly needed are experimentalsocieties!
There is good biological precedent for this idea. In the evolution of life there
are innumerable cases when an organism was clearly dominant, highly specialized,
perfectly acclimatized to its environment. But the environment changed and theorganism died. It is for this reason that nature employs mutations. The vast
majority of mutations are deleterious or lethal. The mutated species are lessadaptive than the normal types. But one in a thousand or one in ten thousand
mutants has a slight advantage over its parents. The mutations breed true, and themutant organism is now slightly better adapted.
Social mutations, it seems to me, are what we need. Perhaps because of a hoaryscience-fiction tradition that mutants are ugly and hateful, it might be better to
use another term. But social mutation – a variation on a social system whichbreeds true, which, if it works, is the path to the future – seems to be precisely
the right phrase. It would be useful to examine why some of us find the phrase
objectionable.
We should be encouraging social, economic, and political experimentation on a
massive scale in all countries. Instead, the opposite seems to be occurring. In
countries such as the United States and the Soviet Union the official policy is to
discourage significant experimentation, because it is, of course, unpopular with the
majority. The practical consequence is vigorous popular disapproval of significant
variation. Young urban idealists immersed in a drug culture, with dress styles
considered bizarre by conventional standards, and with no prior knowledge of
agriculture, are unlikely to succeed in establishing Utopian agriculturalcommunities in the American Southwest – even without local harassment. Yet
such experimental communities throughout the world have been subjected tohostility and violence by their more conventional neighbors. In some cases thevigilantes are enraged because they themselves have only within the previous
generation been accepted into the conventional system.
We should not be surprised, then, if experimental communities fail. Only asmall fraction of mutations succeed. But the advantage social mutations have overbiological mutations is that individuals learn; the participants in unsuccessfulcommunal experiments are able to assess the reasons for failure and canparticipate in later experiments that attempt to avoid the causes of initial failure.
There should be not only popular approval for such experiments, but also
official governmental support for them. Volunteers for such experiments in
Utopia – facing long odds for the benefit of society as a whole – will, I hope, bethought of as men and women of exemplary courage. They are the cutting edge ofthe future. One day there will arise an experimental community that works much
more efficiently than the polyglot, rubbery, hand-patched society we are living in.
A viable alternative will then be before us.
I do not believe that anyone alive today is wise enough to know what such afuture society will be like. There may be many different alternatives, eachpotentially more successful than the pitifully small variety that face us today.
A related problem is that the non-Western, non-technological societies,
viewing the power and great material wealth of the West, are making great strides
to emulate us – in the course of which many ancient traditions, world-views, andways of life are being abandoned. For all we know, some of the alternatives being
abandoned contain elements of precisely the alternatives we are seeking. There
must be some way to preserve the adaptive elements of our societies – painfully
worked out through thousands of years of sociological evolution – while at thesame time coming to grips with modern technology. The principal immediateproblem is to spread the technological achievements while maintaining cultural
diversity.
An opinion sometimes encountered is that the problem is technology itself. I
maintain that it is the misuse of technology by the elected or self-appointed
leaders of societies, and not technology itself, that is at fault. Were we to return tomore primitive agricultural endeavors, as some have urged, and abandon modern
agricultural technology, we would be condemning hundreds of millions of people
to death. There is no escape from technology on our planet. The problem is to use
it wisely.
For quite similar reasons, technology must be a major factor in planetarysocieties older than ours. I think it likely that societies that are immensely wiser
and more benign than ours are, nevertheless, more highly technological than we.
We are at an epochal, transitional moment in the history of life on Earth. Thereis no other time as risky, but no other time as promising for the future of life on
our planet.

Chapter 6: Chauvinism
Jokes are a way of dealing with anxiety. There is a class of jokes dealing withextraterrestrial life. In one, the extraterrestrial visitor lands on Earth, walks up to agasoline pump or a gumball machine – the accounts differ – and asks, "What's anice girl like you doing in a place like this?"Elsewhere, beings are doubtless very different from us. But the joke assumes
that extraterrestrial organisms will be, if not like human beings, then like gasoline
pumps or gumball machines. The most likely circumstance is that extraterrestrial
beings will look nothing like any organisms or machines familiar to us.
Extraterrestrials will be the product of billions of years of independent biologicalevolution, by small steps, each involving a series of tiny mutational accidents, onplanets with very different environments from those that characterize Earth.
But such jokes underscore a general problem and a general virtue in thinking
about life elsewhere. The problem is that we have only one kind of life to study,
the co-related biology of the planet Earth, all organisms of which have descended
from a single instance of the origin of life. It is difficult for the biologist, as well as
the layman, to determine what properties of life on our planet are accidents of theevolutionary process and what properties are characteristic of life everywhere. The
assumption that life elsewhere has to be, in some major sense, like life here is aconceit I will call chauvinism.
While such chauvinism has been common throughout human history, clearer
views have occasionally surfaced, for example, by the great French astronomer
Pierre Simon, the Marquis de Leplace. In his classic work La Mecanique Celeste hewrote: "[The Sun's] influence gives birth to the animals and plants which cover thesurface of the Earth, and analogy induces us to believe that it produces similareffects on the planets; for it is not natural to pose that matter, of which we see thefecundity develop itself in such various ways, should be sterile upon a planet solarge as Jupiter, which, like the Earth, has its days, its nights, and its years, and on
which observation discovers changes that indicate very active forces. Man, formed
for the temperature which he enjoys upon the Earth, could not, according to allappearance, live upon the other planets; but ought there not to be a diversity oforganization suited to the various temperatures of the globes of this universe? If
the difference of elements and climates alone causes such variety in the
production of the Earth, how infinitely diversified must be the production of theplanets and their satellites?" Laplace wrote these words near the end of theeighteenth century.

The virtue of thinking about life elsewhere is that it forces us to stretch ourimaginations. Can we think of alternative solutions to biological problems alreadysolved in one particular way on Earth? For example, the wheel is a comparatively
recent invention on the planet Earth. It seems to have been invented in the ancient
Near East less than ten thousand years ago. In fact, the high civilizations of MesoAmerica, the Aztecs and the Mayas, never employed the wheel, except forchildren's toys. Biology – the evolutionary process – has never invented the wheel,in spite of the fact that its selective advantages are manifest. Why are there nowheeled spiders or goats or elephants rolling along the highways? The answer isclearly that, until recently, there were no highways. Wheels are of use only when
there are surfaces to roll on. Since the planet Earth is a heterogeneous, bumpy
place with few long, smooth areas, there was no advantage to evolving the wheel.
We can very well imagine another planet with enormous long stretches of smoothlava fields in which wheeled organisms are abundant. The late Dutch artist M. C.
Escher designed a salamander-like organism that would do very well in such anenvironment.
The evolution of life on Earth is a product of random events, chancemutations, and individually unlikely steps; small differences early in the evolutionof life have a profound significance later in the evolution of life. Were we to startthe Earth over again and let only random factors operate, I believe that we would
wind up with nothing at all resembling human beings. This being the case, howmuch less likely it is that organisms evolving over five billion or more years,
independently in a quite different environment of another planet of a far-off star,
would closely resemble human beings.
Thus, the hoary science-fiction standby of the sexual love between a humanbeing and an inhabitant of another planet ignores, in the most fundamental sense,
the biological realities. John Carter could love Dejah Thoris, but, despite what
Edgar Rice Burroughs believed, their love could not be consummated. And if it
could, a viable offspring would not be possible. Likewise, the category of contact
story, now quite fashionable in some UFO enthusiast circles, of sexual contact
between human and saucerian – most recently described in a weekly newspaper
headline with the modest title "We Sexed a Blonde from a Flying Saucer!" – must
be relegated to the realm of improbable fantasy. Such crossings are about asreasonable as the mating of a man and a petunia.
A popular phrase – often encountered in popular books on the planets – is "lifeas we know it." We read that "life as we know it" is impossible on this planet orthat. But what is life as we know it? It depends entirely on who the "we" is. A
person who is unsophisticated in biology, who lacks a keen appreciation of themultitudinous adaptations and varieties of terrestrial organisms, will have a meager
idea of the range of possible biological habitats. There are discussions, even by
famous scientists, that give the impression that an environment that is
uncomfortable for my grandmother is impossible for life.
At one time it was thought that oxides of nitrogen had been detected in theatmosphere of Mars. A scientific paper was published on this apparent finding.
The authors of the paper argued that life on Mars was, therefore, impossible,
because oxides of nitrogen are poisonous gases. There are at least two objections
to this argument. First, oxides of nitrogen are poisonous gases only to someorganisms on Earth. Second, what quantity of oxides of nitrogen were thought tobe discovered on Mars? When I calculated the amount, it turned out to be lessthan the average abundance above Los Angeles. The oxides of nitrogen are an
important constituent of smog. Life in Los Angeles may be difficult, but it is not
yet impossible. The same conclusion applies to Mars. The final problem withthese particular observations is that they are very likely mistaken; later studies –for example, observations Tobias Owen and I made with the Orbiting
Astronomical Observatory – have shown no oxides of nitrogen in the atmosphereof Mars.
Oxygen chauvinism is common. If a planet has no oxygen, it is alleged to beuninhabitable. This view ignores the fact that life arose on Earth in the absence ofoxygen. In fact, oxygen chauvinism, if accepted, logically demonstrates that life
anywhere is impossible. Fundamentally, oxygen is a poisonous gas. It chemicallycombines with and destroys the organic molecules of which terrestrial life iscomposed. There are many organisms on Earth that do without oxygen and manyorganisms that are poisoned by it.
All of the earliest organisms on Earth did not use molecular oxygen, O2. In abrilliant set of evolutionary adaptations, organisms like insects and frogs and fishand people learned not only to survive in the presence of this poisonous gas but
actually to use it to increase the efficiency with which we metabolize foodstuffs.
But that should not blind us to the fundamentally poisonous character of this gas.
The absence of oxygen on a place such as Jupiter is, therefore, hardly an argument
against life on such planets.
There are ultraviolet light chauvinists. Because of the oxygen in the Earth's
atmosphere, a variety of oxygen molecule called ozone (O3) is produced high inthe atmosphere, about twenty-five miles above the surface. This ozone layer
absorbs the middle-wavelength ultraviolet rays from the Sun, preventing themfrom reaching the surface of our planet. These rays are germicidal. They areemitted by ultraviolet lamps commonly used to sterilize surgical instruments.
Strong ultraviolet rays from the Sun are an extremely serious hazard to most formsof life on Earth. But this is because most forms of life on Earth evolved in theabsence of a high ultraviolet flux.
It is easy to imagine adaptations to protect organisms against ultraviolet light. In
fact, sunburn and high melanin pigmentation in the skin are adaptations in thisdirection. They have not been carried very far in most terrestrial organisms
because the present ultraviolet flux is not very high. In a place like Mars, where
there is little ozone, the ultraviolet light at the surface is extremely intense. But
the Martian surface material is a strong absorber of ultraviolet light – as most soil
and rocks are – and we can easily imagine organisms walking around with small
ultraviolet-opaque shields on their backs: Martian turtles. Or perhaps Martianorganisms carry about ultraviolet parasols. Many organic molecules also could be
used in the exterior layers of extraterrestrial organisms to protect them against
ultraviolet light.
There are temperature chauvinists. It is said that the freezing temperatures onplanets like Jupiter or Saturn, in the outer Solar System, make all life there
impossible. But these low temperatures do not apply to all portions of the planet.
They refer only to the outermost cloud layers – the layers that are accessible toinfrared telescopes that can measure temperatures. Indeed, if we had such atelescope in the vicinity of Jupiter and pointed it at Earth, we would deduce very
low temperatures on Earth: We would be measuring the temperatures in theupper clouds and not on the much warmer surface of Earth.
It is now quite firmly established, both from theory and from radio
observations of these planets, that as we penetrate below the visible clouds, thetemperatures increase. There is always a region in the atmospheres of Jupiter,
Saturn, Uranus, and Neptune that is at quite comfortable temperatures byterrestrial standards.
But why is it necessary to have temperatures like those on Earth in order forlife to proliferate? A human being is seriously inconvenienced if his bodytemperature is raised or lowered by a mere 20 degrees. Is this because we happen
to live by accident on the one planet in the Solar System that has a surface at theright temperature for biology? Or is it that our chemistry is delicately attuned tothe temperature of the planet on which we have evolved? The latter is almost
surely the case. Other temperatures, other biochemistries.
Our biological molecules are put together in complex three-dimensional

arrangements. The functioning of these molecules, particularly the enzymes, areturned on and off by altering these three-dimensional arrangements. The chemicalbonds that do these rearrangements must be weak enough to be broken
conveniently at terrestrial temperatures, and at the same time strong enough not
to fall to pieces if left alone for short periods of time. A chemical bond known as
the hydrogen bond has an energy appropriately intermediate between these
unreactive and unstable alternatives. The hydrogen bond is intimately connectedwith the three-dimensional biochemistry of terrestrial organisms.
On a much hotter planet like Venus, our biological molecules would fall topieces. On a much colder planet in the outer Solar System, our biologicalmolecules would be rigid, and our chemical reactions would not proceed at any
useful rate. However, it is conceivable that much stronger bonds on Venus andmuch weaker bonds in the outer Solar System play the same role that hydrogenbonds play on Earth. We may have been much too quick to reject life attemperatures very different from those on our planet. There are not many
chemical reactions known that can proceed at useful rates at some very low
temperature such as might exist on Pluto, 30 or 40 degrees above absolute zero.
But there are also very few chemical laboratories on Earth where experiments are
performed at 30 or 40 degrees above absolute zero. With a few exceptions, such
experiments have not been performed at all.
We are thus at the mercy of observational selection. We examine only a small
fraction of the possible range of cases because of some unconscious bias, or thefact that scientists wish to work in their shirtsleeves. We then conclude that allconceivable cases must conform to what our preconceptions have forced upon us.
Another common chauvinism – one which, try as I might, I find I share – iscarbon chauvinism. A carbon chauvinist holds that biological systems elsewhere in
the universe will be constructed out of carbon compounds, as is life on this planet.
There are conceivable alternatives: Atoms like silicon or germanium can enter intosome of the same kinds of chemical reactions as carbon does. It is also true thatmuch more attention has been paid to carbon organic chemistry than to silicon or
germanium organic chemistry, largely because most biochemists we know are of
the carbon, rather than the silicon or germanium, variety. Nevertheless, from what
we know of the alternative chemistries, it appears clear that – except in very lowtemperature environments – there is a much wider variety of complex
compounds that can be built from carbon than from the alternatives.
In addition, the cosmic abundance of carbon exceeds that of silicon,
germanium, or other alternatives. Everywhere in the universe, and particularly inprimitive planetary environments in which the origin of life occurs, there is simplymore carbon than alternative atoms available to make complex molecules. We see
from laboratory experiments simulating the primitive atmosphere of the Earth or
the present environment of Jupiter, as well as in radioastronomical studies of theinterstellar medium, a profusion of simple and complex organic molecules readily
produced by a wide variety of energy sources. For example, in one of ourexperiments, the passage of a single high-pressure shock wave through a mixtureof methane (CH4), ethane (C2H6), ammonia (NH3), and water (H2O) converted 38
percent of the ammonia into amino acids, the building blocks of proteins. There
were not enormous quantities of other sorts of organic molecules.
Thus, both the atoms and the simple molecules of which we are made areprobably common to organisms elsewhere in the universe. But the specific way inwhich these molecules are put together and the specific forms and physiologies ofthe extraterrestrial organisms may be, because of their different evolutionary
histories, extremely different from what is common on our planet.
In considering which stars to examine for possible radio signals directed at us,much attention is usually given to stars like our Sun. It has been reasonably argued
that searches should begin with the one type of star we know has life on at least
one of its planets, namely stars like our own Sun. In Project Ozma, the firstattempt to search for such radio signals, the two stars examined, Tau Ceti and
Epsilon Eridani, were both stars with mass, radius, age, and composition very
similar to our Sun, which astronomers call a G-0 dwarf. They were, in fact, thenearest two Sun-like stars.
But should we restrict our attention to stars like the Sun? I think not. Stars ofslightly smaller mass and of slightly lower luminosity than our Sun are longer lived.
These stars, called K and M dwarfs, can be many billions of years older than theSun. If we imagine that the longer the lifetime of a planet, the more likely it is that
intelligent organisms have evolved on it, we should then bias our searches toward
K and M stars and avoid G-star chauvinism. It may be objected that planets of K
and M stars are much colder than Earth, and that life on them may be less likely.
The premise of this objection does not appear to be true; such planets seem to becloser to their stars than the corresponding planets in our Solar System; and wehave already discussed the fallacies of temperature chauvinism. Too, there aremany more K and M stars than G stars.
Is there planetary chauvinism? Must life arise and reside on planets, or might
there be organisms that inhabit the depths of interstellar space, the surfaces orinteriors of stars, or other even more exotic cosmic objects?

In our present state of ignorance, these are very difficult questions to answer.
The density of matter in interstellar space is so low that an organism there simply
cannot acquire enough material to make a copy of itself in any reasonable periodof time. This is not true in dense interstellar clouds, but such clouds live for very
short periods of time, condensing to form stars and planets. In the process, they
become so hot that any organic compounds contained within them are probably
destroyed.
We might imagine organisms evolving on planets with atmospheres slowly
leaking away to space, permitting the organisms gradually to adapt to theincreasingly severe conditions, and finally acclimatizing to what in effect is aninterstellar environment. Organisms leaving such planets – perhaps byelectromagnetic radiation pressure, or by solar wind from the local sun – might
populate interstellar space, but they would still be faced with insurmountableproblems of malnutrition.
A quite different sort of interstellar organism may be much more likely:Intelligent beings who arise on planets as we have, but who have moved their
arena of activities to the much vaster volume of interstellar space. Beings in our far
technological future should have capabilities at which we cannot today even dimly
guess. It is not out of the question that such societies could tap the matter andenergy of stars and galaxies for their own uses. Just as we are organisms completely
at home only on the land, although we evolved from the sea, the universe may be
populated with societies that arose on planets but that are comfortable only in thedepths of interstellar space.

Chapter 7: Space Exploration as a Human Enterprise
I. The Scientific Interest
There is a place with four suns in the sky – red, white, blue, and yellow; two ofthem are so close together that they touch, and star-stuff flows between them.
I know of a world with a million moons.
I know of a sun the size of the Earth – and made of diamond.
There are atomic nuclei a mile across that rotate thirty times a second.
There are tiny grains between the stars, with the size and atomic compositionof bacteria.
There are stars leaving the Milky Way. There are immense gas clouds falling
into the Milky Way.
There are turbulent plasmas writhing with X- and gamma-rays and mighty
stellar explosions.
There are, perhaps, places outside our universe.
The universe is vast and awesome, and for the first time we are becoming apart of it.
The planets are no longer wandering lights in the evening sky. For centuries,
Man lived in a universe that seemed safe and cozy – even tidy. Earth was thecynosure of creation and Man the pinnacle of mortal life. But these quaint andcomforting notions have not stood the test of time. We now know that we live ona tiny clod of rock and metal, a planet smaller than some relatively minor featuresin the clouds of Jupiter and inconsiderable when compared with a modest
sunspot.
Our star, the Sun, is small and cool and unprepossessing, one of some two
hundred billion suns that make up the Milky Way Galaxy. We are located so far
from the center of the Milky Way that it takes light, traveling at 186,000 miles asecond, some 30,000 years to reach us from there. We are in the galactic
boondocks, where the action isn't. The Milky Way Galaxy is entirely
unremarkable, one of billions of other galaxies strewn through the vastness ofspace.

No longer does "the world" mean "the universe." We live on one world among
an immensity of others.
Charles Darwin's insights into natural selection have shown that there are no
evolutionary pathways leading unerringly from simple forms to Man; rather,evolution proceeds by fits and starts, and most life forms lead to evolutionary
dead-ends. We are the products of a long series of biological accidents. In thecosmic perspective there is no reason to think that we are the first or the last or
the best.
These realizations of the Copernican and Darwinian revolutions are profound –and, to some, disturbing. But they bring with them compensatory insights. We
realize our deep connectedness with other life forms, both simple and complex.
We know that the atoms that make us up were synthesized in the interiors ofprevious generations of dying stars. We are aware of our deep connection, both inform and in matter, with the rest of the universe. The cosmos revealed to us by
the new advances in astronomy and biology is far grander and more awesome than
the tidy world of our ancestors. And we are becoming a part of it, the cosmos as itis, not the cosmos of our desires.
Mankind now stands at several historical branching points. We are on thethreshold of a preliminary reconnaissance of the cosmos. For the first time in his
history, Man is capable of sending his instruments and himself from his home
planet to explore the universe around him.
But the exploration of space has been defended largely in terms of narrowconsiderations of national prestige, both in the United States and in the Soviet
Union; in terms of the development of technological capabilities, in an age whenmany people are finding the development of technology for its own sake to havedisastrous consequences; in terms of technological "spinoff" when the space
program costs very much more than the cost of direct development of the spinoff;and in terms of a quite tenuous argument for military advantage, in a time whenpeople the world over long for a demilitarization of society.
Under these circumstances, it is not surprising that hard questions are being
asked about expenditures in space, when there are visible and urgent needs forfunds to correct injustices and improve society and the quality of life on Earth.
These questions are entirely appropriate. If scientists cannot give to the man on
the street a satisfactory explanation of expenditures in the exploration of space, it
is not obvious that public funds should be allocated for such ventures.

The interest of an individual scientist in space exploration is likely to be very
personal – something puzzles him, intrigues him, has implications that excite him.
But we cannot ask the public to spend large sums just to satisfy the scientist's
curiosity. When we probe more deeply into the professional interests of individual
scientists, however, we often find a focus of concern that largely overlaps the
public interest.
A fundamental area of common interest is the problem of perspective. The
exploration of space permits us to see our planet and ourselves in a new light. We
are like linguists on an isolated island where only one language is spoken. We canconstruct general theories of language, but we have only one example to examine.
It is unlikely that our understanding of language will have the generality that amature science of human linguistics requires.
There are many branches of science where our knowledge is similarly
provincial and parochial, restricted to a single example among a vast multitude ofpossible cases. Only by examining the range of cases available elsewhere can abroad and general science be devised.
The science that has by far the most to gain from planetary exploration isbiology. In a very fundamental sense, biologists have been studying only one formof life on Earth. Despite the apparent diversity of terrestrial life forms, they are
identical in the deepest sense. Beagles and begonias, bacteria and baleen whales all
use nucleic acids for storage and transmission of hereditary information. They all
use proteins for catalysis and control. All organisms on Earth, so far as we know,
use the same genetic code. The cross-sectional structures of human sperm cells arealmost identical with those of the cilia of paramecia. Chlorophyll and hemoglobin
and the substances responsible for the coloring of many animals are all essentiallythe same molecule.
It is difficult to escape the conclusion – which, in a sense, is implicit inDarwinian natural selection – that all life on Earth has evolved from a single
instance of the origin of life. If this is true, there is an important sense in which thebiologist cannot distinguish the necessary from the contingent, that is, distinguish
those aspects of life that any organism anywhere in the universe must have simply
in order to be alive, from those aspects of life that are the results of the tortuous
evolution by small opportunistic adaptations.
The production of simple organic (carbon-based) molecules under simulated
primitive planetary conditions is now subject to active laboratory investigation. As

we saw earlier, the molecules of which we are made can be produced rather easily,in the absence of life, under quite general primitive planetary conditions. But it is
not practicable to perform laboratory experiments on even the early stages of
biological evolution: The time scales are too long. It is only by examining living
systems elsewhere that biologists can determine what other possibilities there are.
It is for this reason that the discovery of even an extremely simple organism on
Mars would have profound biological significance. On the other hand, if Mars
proves to be lifeless, a natural experiment has been performed for us: Two planets,
in many respects similar; but on one life has evolved, on the other it has not. By
comparing the experimental with the control planet, much may be discovered
about the origin of life. Similarly, the search for prebiological organic chemicals on
the Moon, on Mars, or on Jupiter is of great importance in understanding the steps
leading to the origin of life.
As another example of the perspective provided by planetary studies, consider
meteorology. The problems of turbulent flow and fluid dynamics are among themost difficult in all of physics. Some insights into the Earth's weather have beenobtained by standing back and examining, by photography from meteorologicalsatellites, the circulation of the Earth's atmosphere. Still, meteorological theory for
the Earth is today capable of long-range weather predictions, but only over verylarge geographical areas, for a range of simplifying assumptions, and for only a little
time into the future. Laboratory studies of atmospheric circulation have a limited
scope; classically, they are performed in modified dishpans.
It would be nice to do a "Joshua" experiment, stopping the Earth from turning
for a while. The change in circulation would provide insights into the role of the
Earth's rotation (particularly through Coriolis forces) in determining thecirculation. But such an experiment is technologically very difficult. It also has
undesirable side-effects. On the other hand, the planet Venus, with approximately
the same mass and radius as Earth, has a rotation rate 240 times slower – so slowthat Coriolis forces will be minor. The atmosphere is much thicker on Venus thanon Earth. Nature has arranged a natural experiment for the meteorologists.
Jupiter rotates about once every ten hours; here is an enormous planet thatturns faster than Earth does. The effects of rotation should be much more
important than on Earth, and, indeed, Jupiter gives the impression of having aseething, roiling, turbulent atmosphere; its prominent atmospheric bands and belts
are almost certainly related to the rapid rotation. Nature has arranged two
comparison experiments – two planets with massive atmospheres, one rotating
slowly, the other rapidly. An understanding of the circulation of the massive
atmospheres of Venus and Jupiter will improve our understanding of oceanic, as
well as atmospheric, circulation on Earth.

Or consider the planet Mars. Here is a planet with – quite remarkably – thesame period of rotation and the same inclination of its axis of rotation to its orbital
plane as Earth. But its atmosphere is only 1 percent of ours, and it has no oceans
and no liquid water. Mars is a control experiment on the influence of oceans andliquid water on atmospheric circulation.
Until recently, the geologist has been restricted to one object of study, theEarth. He was unable to decide which properties of the Earth are fundamental to
all planetary surfaces and which are peculiar to the unique circumstances of Earth.
For example, seismographic observations of earthquakes have revealed the interior
structure of Earth and its division into crust, mantle, liquid metal core, and solid
inner core. But the reason Earth is so divided remains largely obscure. Was Earth's
crust exuded from the mantle through geological time? Did it fall from the skies inan early catastrophic event? Has Earth's core formed gradually through geologicaltime by the sinking of iron through the mantle? Or did it form discontinuously,
perhaps in a molten Earth at the time of the origin of our planet? Such questions
can be examined by performing seismometric observations on the surfaces ofother planets; they could be relatively inexpensive experiments performed
automatically by existing instrumentation.
There is now reasonably convincing evidence of continental drift. The motionof Africa and South America away from each other is the best-known example. In
some theories, the driving force of continental drift and of the evolution of theinterior of our planet are connected – for example, through convection currents
circulating slowly between core and crust in the mantle. Such connections
between surface geology and planetary interiors are just beginning to emerge in the
study of other planets. We test our understanding of such connections by testingwhether they apply elsewhere.
The perspectives gained in studies like these have a range of practicalconsequences. A generalization of the science of meteorology may lead to great
improvements in weather forecasting. It may even lead to weather modification.
The study of the atmosphere of Venus has already led to the theory that a
runaway "greenhouse" effect has occurred there – an unstable equilibrium inwhich an increase in temperature leads to an increase in the atmospheric water
vapor content, leading through infrared absorption of thermal radiation from theplanet to a yet further increase in surface temperature, and so on. Had Earthstarted out only slightly closer to the Sun than it did, preliminary theoreticalestimates indicate that we might have ended up as a searing hot Venus. But welive in a time when the atmosphere of Earth is being strongly modified by theactivities of Man. It is of the first importance to understand precisely what
happened on Venus so that an accidental recapitulation on Earth of the runaway
Venus greenhouse can be avoided.
The studies of the surfaces and interiors of the planets may be of great practicalbenefit in earthquake prediction and in remote geological prospecting for mineralsof value on Earth.
The revolution in biology that the discovery of indigenous life elsewhere would
surely bring may have a range of unsuspected practical benefits, particularly to theextent that research in cancer and aging is now limited by ideas rather than money.
The study of the highly condensed matter in neutron stars and the enormous
energy productions in the centers of galaxies and in quasars has already led tosuggestions about possible modifications of the laws of physics, laws that havebeen deduced on Earth to explain phenomena observed on Earth.
The exploration of space will inevitably provide a wealth of practical benefits.
But the history of science suggests that the most important of these will be
unexpected – benefits we are today not wise enough to anticipate.

Chapter 8: Space Exploration as a Human Enterprise
II. The Public Interest
Direct scientific interest in space exploration and the practical consequences thatcan be imagined flowing from them are not the principal or even the most generalinterests that space exploration holds for the layman. There is today – in a time
when old beliefs are withering – a kind of philosophical hunger, a need to know
who we are and how we got here. There is an ongoing search, often unconscious,
for a cosmic perspective for humanity. This can be seen in innumerable ways, but
most clearly on the college campus. There, an enormous interest is apparent in arange of pseudoscientific or borderline-scientific topics – astrology, Scientology,
the study of unidentified flying objects, investigation of the works of Immanuel
Velikovsky, and even science-fiction superheroes – all of which represent anattempt, overwhelmingly unsuccessful in my view, to provide a cosmic
perspective for mankind. Professor George Wald, of Harvard, is thinking of thislonging for a cosmic perspective when he writes: "We have desperately to find ourway back to human values. I would even say to religion. There is nothing
supernatural, in my mind. Nature is my religion, and it's enough for me… What I
mean is: We need some widely shared view of the place of Man in the Universe."
The most widely sold book in college communities from Cambridge,
Massachusetts, to Berkeley, California, in recent years was called The Whole Earth
Catalog, which viewed itself as providing access to tools for the creation ofcultural alternatives. What was striking was the number of works displayed in theCatalog that related to a scientific cosmic perspective. They ranged from the
Hubble Atlas of Galaxies to flags and posters of Earth photography near full phase.
The title of The Whole Earth Catalog derives from its founder's urge to see a
photograph of our planet as a whole. The Fall 1970 issue expanded thisperspective, showing a photograph of the whole Milky Way Galaxy.
There is a similar trend apparent in some modern art and in rock 'n' roll music:"Cosmo's Factory" by Creedence Clearwater Revival, "Starship" by the Jefferson
Airplane, "Mr. Spaceman" and "CTA 102" by the Byrds, "Mr. Rocket Man" by
Elton John, and many others.
Such interest is not restricted to the young. There is a tradition in the UnitedStates of public-subscription support of astronomy. Construction of entire
observatories and salaries for staff have been paid for voluntarily by the local
communities. Several million people visit planetariums in North America andBritain each year.

The current resurgence of interest in the ecology of the planet Earth is also
connected with this longing for a cosmic perspective. Many of the leaders of theecological movement in the United States were originally stimulated to action byphotographs of Earth taken from space, pictures revealing a tiny, delicate, andfragile world, exquisitely sensitive to the depredations of man – a meadow in the
middle of the sky.
As the results of space exploration and their accompanying new perspectives
on Earth and its inhabitants permeate our society, they must, I believe, haveconsequences in literature and poetry, in the visual arts and music. The
distinguished American physicist Richard Feynman writes: "It does no harm to themystery to know a little about it. For far more marvelous is the truth than any
artists of the past imagined! Why do the poets of the present not speak of it?
What men are poets who can speak of Jupiter if he were like a man, but if he is animmense spinning sphere of methane and ammonia must be silent?"
But mere general exploration does not yet motivate pervasive public interest in
space. For many, the rocks returned from the Moon were a great disappointment.
They were seen as merely rocks. What role they might play in chronicling the daysof creation of the Earth-Moon system has not yet been explained adequately tothe public.
Where public interest in space is most apparent is in cosmology and in the
search for extraterrestrial life, topics that strike resonant chords in a significant
fraction of mankind. The fact that much more newspaper space is given to themost casual hypothesis on exobiology than to many of the most careful andimportant results in other areas is an accurate reflection of where public interest
lies. The discovery of interstellar microwave lines of formaldehyde and hydrogencyanide has been widely described in the public press as connected, through a longset of linkages, to questions in biology.
While it is true that the average person thinks in terms of mild variants ofhuman beings when he is asked to imagine extraterrestrial life, it is also true thatinterest even in Martian microbes is much larger than in many other areas of space
exploration. The search for extraterrestrial life could be a keystone of public
support for space experiments – experiments oriented both within and beyond
the Solar System.
There are many possible viewpoints on the present and near-future costs ofspace science and astronomy. Because the annual costs of ground-based astronomy
are only a few percent of the costs of the scientific space program, I willconcentrate on the price of the latter. It is customary to compare expenditures on
space to annual expenditures in the United States for ethyl alcohol or bubble gum
or cosmetics. I personally find it more useful to compare the costs with those of
the U. S. Department of Defense. Using a report of the government's General
Accounting Office (the New York Times, July 19, 1970), we learn that the total
anticipated cost of the Viking mission to land on Mars in 1976 is about half that of
the cost overruns in the so-called Safeguard antiballistic missile system for fiscal
year 1970. The cost of a Grand Tour exploration of all the planets in the outer
Solar System (canceled for lack of funds) is comparable to the 1970 cost overruns
on the Minuteman III system; the cost of a very large optical telescope in space,capable of definitive studies of the origins of the universe, is comparable to the1970 cost overruns on the Minuteman II missile; and a major program of Earthresources satellites, involving several years of close inspection of the surface andweather of our planet, would cost approximately the fiscal year 1970 cost overruns
on the P-3C aircraft. A decade-long program of systematic investigation of theentire Solar System would cost as much as the accounting mistakes on a single"defense" weapons system in a single year. The scientific space program is smallchange compared to the errors in the Department of Defense budget.
Another viewpoint worth considering is space exploration as entertainment. A
Viking Mars-lander could be completely funded through the sale, to every
American, of a single issue of a magazine, containing pictures taken on the surfaceof Mars by Viking. Photographs of the Earth, the Moon, the planets, and spiral andirregular galaxies are an appropriate and even characteristic art form of our age.
Such novel and oddly moving photographs as the Lunar Orbiter image of theinterior of the crater Copernicus and the Mariner 9 photography of the Martian
volcanoes, windstreaks, moons, and polar icecaps speak both to a sense of wonder
and to a sense of art. An unmanned roving vehicle on Mars could probably be
supported by subscription television. A phonograph record of the output of a
microphone on Mars, where there seems to be a great deal of acoustic energy,
might have wide sales.
I do not wish here to broach the debate on manned vs. unmanned planetary
exploration, except to stress again that there may be very good nonscientificreasons for sending men into space. There exist intermediate cases between
manned and unmanned exploration, which we may very well see in theforthcoming decades. For example, there may be telepuppets, devices landed onanother planet but fully controlled by an individual human being in orbit, all of
whose senses are in a feedback loop with the device. It is also possible that planetswith very hostile environments by terrestrial standards, or planets where there is agreat danger of contamination by terrestrial micro-organisms, will be explored bymen inside machines like enormous prosthetic devices, amplifying the sense
perceptions and muscular abilities of the human operator.
Even apart from these hypothetical developments, it is already quite clear thatthe development of sophisticated devices for unmanned planetary exploration isorganizing the same technology required for the production of useful robots on the
Earth. An unmanned vehicle that lands on Mars by the early 1980s will very likely
have the ability to sense its environment much more thoroughly than humans areable to, to rove over the landscape, to make both preprogrammed decisions anddecisions based on information newly acquired. First cousins to such a robot, somemass-produced, would be extremely useful devices here on Earth. I am thinking inpart of operations in inaccessible environments such as the abyssal floor of theocean basins, but I am also thinking of industrial robots to free workers from
repetitive and uninteresting tasks, and domestic robots to liberate the housekeeper
from a life of drudgery.
The experience of space exploration gives no unique philosophy; to someextent, each group tends to see its own philosophical view reflected, and notalways by the soundest logic: Nikita Khrushchev stressed that in the space flight ofYuri Gagarin no angels or other supernatural beings were detected; and, in almost
perfect counterpoint, the Apollo 8 astronauts read from lunar orbit the Babylonian
cosmogony enshrined in Genesis, Chapter 1, as if to reassure their American
audience that the exploration of the Moon was not really in contradiction toanyone's religious beliefs. But it is striking how space exploration leads directly toreligious and philosophical questions.
I believe that military control of manned space flight – in practice in the Soviet
Union and a subject of current debate in the United States – is a step that
supporters of peace should back. The military establishments of the United States
and the Soviet Union are, I am afraid, establishments with vested interests in war.
They are meticulously trained for war; in time of war, there are rapid promotions,increases in pay, and opportunities for valor that are absent in peacetime. Where
eager readiness for warfare exists, the likelihood of intentional or accidental
warfare becomes much greater. By virtue of their training and temperament,
military men are often not interested in other sorts of gainful employment. There
are few other ways of life with the perquisites of power of the military officer. If
peace broke out, the officer corps, their services no longer as necessary, would be
profoundly discomfited. Premier Khrushchev once attempted to cashier a large
number of senior officers in the Red Army, putting them in charge ofhydroelectric power stations and the like. This was not to their liking, and insomething like a year most of them were back in their old jobs. In fact, themilitary establishments in the United States and the Soviet Union owe their jobs
to each other, and there is a very real sense in which they form a natural allianceagainst the rest of us.
At the same time, there are enormous labor forces and huge electronics,
missile, and chemical industries that have an equally strong vested interest in andmaintain equally strong lobbies for the maintenance of the warfare state. Barringsome awesomely atypical epidemic of reason, is there not some way that thispowerful collection of vested interests could be moved toward more peacefulactivities? Space exploration requires exactly this combination of talents andcapabilities. It requires a large technical base in such areas as electronics, computer
technology, precision machinery, and aerospace frames. It requires something very
close to military organization to keep a large number of geographically dispersed
enterprises moving in phase toward a common goal.
The history of the exploration of the Earth's surface has largely been a militaryhistory, in part because it is an appropriate application of military traditions oforganization and personal valor. It is the other military traditions that pose a
danger to us today. Perhaps the exploration of the Solar System is an alternativeand honorable employment for the military and industrial vested interests. I canimagine a transition to an arrangement where a significant fraction of the career
officer corps of both the United States and the U.S.S.R. is transferred to space
exploration. At least in part because of their considerable abilities, a fair numberof military officers are employed by the National Aeronautics and Space
Administration in activities with little or no military significance. And of course
the vast majority of astronauts and cosmonauts have been military officers. This issurely all to the good: The more of them engaged up there, the less of themengaged down here.
Despite many NASA press releases, much of the space program and almost allof its space science and applications program are in the long run not gimmicky orparochial in perspective. Indeed, they share a community of philosophical,
exploratory, and human interest with many segments of American society – evensegments that are in strong mutual disagreement on many issues. The cost of space
exploration seems very modest compared with its potential returns.

Chapter 9: Space Exploration as a Human Enterprise
III. The Historical Interest
In the long view, the greatest significance of space exploration is that it will
irreversibly alter history. As we mentioned in Chapter 1, the group with which
Man identifies has gradually broadened during this history of mankind. Today thebulk of the world's population has at least a major personal identification withnational superstates. While progress has not been smooth, and there are occasional
reversals, the trend is clearly toward a group identification with mankind as awhole. Space exploration can hasten this identification. Astronauts andcosmonauts have remarked with great feeling about the beauty and serenity of the
Earth viewed from space. For many of them, a flight into space has been areligious experience, transfiguring their lives. National boundaries do not appear inphotographs of Earth from space. As Arthur C. Clarke somewhere remarked, it isdifficult to imagine even the most fervent of nationalists not reconsidering his
views as he sees the Earth fade from a faint crescent to a tiny point of light, lost
among millions of stars.
Space exploration provides a calibration of the significance of our tiny planet,
lost in a vast and unknown universe. The search for life elsewhere will almost
surely drive home the uniqueness of Man: The winding, unsure, improbable,
evolutionary pathway that has brought us to where we are; and the improbabilityof finding – even in a universe populated with other intelligences – one with aform very much like our own. In this perspective, the similarities among men will
stand out overwhelmingly against our differences.
There is a practical geocentrism to our everyday life. We still talk about the
Sun rising and setting rather than the Earth turning. We still think of the universe
organized for our benefit and populated only by us. Space exploration will bringalso a little humility.
Harold Urey has perceptively referred to the space program as a kind ofcontemporary pyramid-building. Seen in the context of Pharaonic Egypt, theanalogy seems particularly apt, for the pyramids were an attempt to deal withproblems of cosmology and immortality. In the long historical perspective, this isprecisely what the space program is about. The footprints left by astronauts on theMoon will survive a million years, and the miscellaneous instruments and packing
cases left there may last as long as the Sun.
On the other hand, the pyramids are monumental and, we today believe, futile

efforts to insure the survival after death of one man, the Pharaoh. Perhaps a better
analogy is with the ziggurats, the terraced towers of the Sumerians andBabylonians – the places where the gods came down to Earth and the population
as a whole transcended everyday life. There is no doubt a little of the pyramid in
the great rocket boosters; but I think their ultimate significance is more likely to
be as contemporary ziggurats.
A society engaged in a relatively modest, peaceful, and intellectually significant
exploration of its surroundings garners thereby the possibility of achieving
greatness. It is difficult to prove such causal chains, and, historically, there are no
one-to-one correlations. But it is remarkable that the nations and epochs marked
by the greatest flowering of exploration are also marked by the greatest cultural
exuberance. In part, this must be because of the contact with new things, newways of life, and new modes of thought unknown to a closed culture, with its vastenergies turned inward.
There are examples from the Biblical Near East, from Periclean Athens, andfrom other times, but I am most taken by the example of the age of European
exploration and discovery. The vernacular languages of France, England, and Iberia
found a definitive literary expression at the same time that the earliest
transatlantic voyages of discovery were occurring. Rabelais and Montaigne inFrance; Shakespeare, Milton, and the translators of the King James Bible inEngland; Cervantes and Lope de Vega in Spain; Camoens in Portugal, all date fromthis period. From the writings of Francis Bacon it is clear that exposure to newparts of the world had a profound influence on the thinking of the times. This
period saw the invention of such fundamental instruments as the telescope, themicroscope, the thermometer, the barometer, and the pendulum clock.
It was also the epoch of Galileo (1564-1642), who, while not resident in one of
the new exploratory nations, was closely tied to one of them – Holland, where thetelescope that he improved upon was first invented. Many of the works of graphic
art during this period – for example, those of Hieronymus Bosch and El Greco –reflect the spirit of change that permeated the times. It was the era of theestablishment of modern physics by Isaac Newton. Descartes, Hobbes, andSpinoza – pivotal individuals in the history of philosophy – flourished. In theactivities and writings of da Vinci, Gilbert, Galileo, and Bacon, the period also
corresponds to the origin of the experimental method in science.
An interesting case history is provided by Holland, a country that has provided
more than its fair share of men of learning and culture. If there was one momentof cultural efflorescence in Holland, it was the period centered around the last half

of the seventeenth century. Iberian ports were inaccessible to the Dutch Republic
because of the war between France and Spain. Forced to find its own sources oftrade, Holland founded the Dutch East and West India Companies. A significant
fraction of the national resources was put into seafaring; one consequence was that
Holland became – for the only time in its history – a world power. Because of
these ventures, Dutch is spoken in Indonesia today, and several individuals of
Dutch ancestry rose to the Presidency of the United States. Far more important is
the fact that, during the same period, Vermeer and Rembrandt, Spinoza and van
Leeuwenhoek flourished in Holland. It was a tightly knit society: Van
Leeuwenhoek, was, in fact, the executor of Vermeer's estate. Holland was themost liberal and least authoritarian nation in Europe during this time.
In all the history of mankind, there will be only one generation that will be firstto explore the Solar System, one generation for which, in childhood, the planets
are distant and indistinct discs moving through the night sky, and for which, in oldage, the planets are places, diverse new worlds in the course of exploration.
There will be a time in our future history when the Solar System will be
explored and inhabited. To them, and to all who come after us, the present
moment will be a pivotal instant in the history of mankind. There are not many
generations given an opportunity as historically significant as this one. The
opportunity is ours, if we but grasp it. To paraphrase K. E. Tsiolkovsky, thefounder of astronautics: The Earth is the cradle of mankind, but one cannot live inthe cradle forever.
A human infant begins to achieve maturity by the experimental discovery that
he is not the whole of the universe. The same is true of societies engaged in the
exploration of their surroundings. The perspective carried by space exploration
may hasten the maturation of mankind – a maturation that cannot come too soon.

Part Two: THE SOLAR SYSTEM
There was a time – and very recently – when the idea of the possibility oflearning the composition of the celestial bodies was considered senseless even byprominent scientists and thinkers. That time has now passed. The idea of thepossibility of a closer, direct study of the universe will today, I believe, appear stillwilder. To step out onto the soil of asteroids, to lift with your hand a stone on themoon, to set up moving stations in ethereal space, and establish living rings aroundthe earth, the moon, the sun, to observe Mars from a distance of several tens ofversts, to land on its satellites and even on the surface of Mars – what could be
more extravagant! However, it is only with the advent of reactive vehicles that a
new and great era in astronomy will begin, the epoch of a careful study of thesky… The prime motive of my life is to do something useful for people… That is
why I have interested myself in things that did not give me bread or strength. But I
hope that my studies will, perhaps soon but perhaps in the distant future, yieldsociety mountains of grain and limitless power.
-K. E. Tsiolkovsky, 1912

Chapter 10: On Teaching the First GradeA friend in the first grade asked me to come to talk to his class, which, he assuredme, knew nothing about astronomy but was eager to learn. With the approval of
his teacher, I arrived at his school in Mill Valley, California, armed with twenty or
thirty color slides of astronomical objects – the Earth from space, the Moon, theplanets, exploding stars, gaseous nebulae, galaxies, and the like – which I thought
would amaze and intrigue and, perhaps to a certain extent, even educate.
But before I began the slide show for these bright-eyed and cherubic little
faces, I wanted to explain that there is a big difference between stating what
science has discovered and describing how scientists found it all out. It is pretty
easy to summarize the conclusions. It is hard to relate all the mistakes, false leads,
ignored clues, dedication, hard work, and painful abandonment of earlier views
that go into the initial discovery of something interesting.
I began by saying, "Now you have all heard that the Earth is round. Everybody
believes that the Earth is round. But why do we believe the Earth is round? Can
any of you think of any evidence that the Earth is round?"For most of the history of mankind, it was reverently held that the Earth is flat– as is entirely obvious to anyone who has stood in a Nebraska cornfield aroundplanting time. The concept of a flat Earth is still built into our language in suchphrases as "the four corners of the Earth." I thought I would stump my little firstgraders and then explain with what difficulty the sphericity of Earth had comeinto general human consciousness. But I had underestimated the first grade of Mill
Valley.
"Well," asked a moppet in the sort of one-piece coverall worn by railroad
engineers, "what about this business of a ship that's sailing away from you, and thelast thing you see is the master, or whatever it's called, that holds up the sail?
Doesn't that mean that the ocean has to be curved?""What about when there's an ellipse of the Moon? That's when the Sun isbehind us and the shadow of the Earth is on the Moon, right? Well, I saw anellipse. That shadow was round, it wasn't straight. So the Earth has to be round.""There's better proof, much better proof," offered another. "What about thatold guy who sailed around the world – Majello? You can't sail around the world if
it isn't round, right? And people today sail around the world and fly around theworld all the time. How can you fly around the world if it isn't round?""Hey, listen, you kids, don't you know there's pictures of the Earth?" added afourth. "Astronauts have been in space, they took pictures of the Earth; you canlook at the pictures, the pictures are all round. You don't have to use all thesefunny reasons. You can see that the Earth is round."And then, as the coup de grâce, one pinafored little girl, recently taken on an
outing to the San Francisco Museum of Science, casually inquired, "What about
the Foucault pendulum experiment?"
It was a very sobered lecturer who went on to describe the findings of modern
astronomy. These children were not the offspring of professional astronomers orcollege teachers or physicians or the like. They were apparently ordinary firstgrade children. I very much hope – if they can survive twelve to twenty years of
regimenting "education" – that they will hurry and grow up and start running
things.
Astronomy is not taught in the public schools, at least in America. With a few
notable exceptions, a student can pass from first to twelfth grade without everencountering any of the findings or reasoning processes that tell us where we arein the universe, how we got here, and where we are likely to be going; without
any confrontation with the cosmic perspective.
The ancient Greeks considered astronomy one of the half dozen or so subjects
required for the education of free men. I find, in discussions with first-graders andhippie communards, congressmen and cab drivers, that there is an enormous
untapped reservoir of interest and excitement in things astronomical. Most
newspapers in America have a daily syndicated astrology column. How many havea daily syndicated astronomy column, or even a science column?
Astrology pretends to describe an influence that pervades people's lives. But it
is a sham. Science really influences people's lives, and in only a slightly less direct
sense. The enormous popularity of science fiction and of such movies as 2001: A
Space Odyssey is indicative of this unexploited scientific enthusiasm. To a very
major extent, science and technology govern, mold, and control our lives – forgood and for ill. We should make a better effort to learn something about them.

Chapter 11: "The Ancient and Legendary Gods of Old"
The sorts of scientific problems that I am involved in – the environments of otherplanets, the origin of life, the possibility of life on other worlds – engage thepopular interest. This is no accident. I think all human beings are excited about
these fundamental problems, and I am lucky enough to be alive at a time when it
is possible to perform scientific investigation of some of these problems.
One result of popular interest is that I receive a great deal of mail, all kinds ofmail, some of it very pleasant, such as from the people who wrote poems andsonnets about the plaque on Pioneer 10; some of it from schoolchildren who wish
me to write their weekly assignments for them; some from strangers who want toborrow money; some from individuals who wish me to check out their detailedplans for ray guns, time warps, spaceships, or perpetual motion machines; andsome from advocates of various arcane disciplines such as astrology, ESP, UFOcontact stories, the speculative fiction of von Danniken, witchcraft, palmistry,phrenology, tea-leaf reading, Tarot cards, the I-Ching, transcendental meditation,and the psychedelic drug experience. Occasionally, also, there are sadder stories,
such as from a woman who was talked to from her shower head by inhabitants ofthe planet Venus, or from a man who tried to file suit against the Atomic Energy
Commission for tracking his every movement with "atomic rays." A number ofpeople write that they can pick up extraterrestrial intelligent radio signals throughthe fillings in their teeth, or just by concentrating in the right way.
But over the years there is one letter that stands out in my mind as the mostpoignant and charming of its type. There came in the post an eighty-five-page
handwritten letter, written in green ballpoint ink, from a gentleman in a mental
hospital in Ottawa. He had read a report in a local newspaper that I had thought itpossible that life exists on other planets; he wished to reassure me that I was
entirely correct in this supposition, as he knew from his own personal knowledge.
To assist me in understanding the source of his knowledge, he thought I would
like to learn a little of his personal history – which explains a good bit of theeighty-five pages. As a young man in Ottawa, near the outbreak of World War II,
my correspondent chanced to come upon a recruiting poster for the American
armed services, the one showing a goateed old codger pointing his index finger atyour belly button and saying, "Uncle Sam Wants You." He was so struck by thekindly visage of gentle Uncle Sam that he determined to make his acquaintance
immediately. My informant boarded a bus to California, apparently the mostplausible habitation for Uncle Sam. Alighting at the depot, he inquired where
Uncle Sam could be found. After some confusion about surnames, my informant
was greeted by unpleasant stares. After several days of earnest inquiry, no one inCalifornia could explain to him the whereabouts of Uncle Sam.
He returned to Ottawa in a deep depression, having failed in his quest. But
almost immediately, his life's work came to him in a flash. It was to find "theancient and legendary gods of old," a phrase that reappears many times throughout
the letter. He had the interesting and perceptive idea that gods survive only solong as they have worshipers. What happens then to the gods who are no longer
believed in, the gods, for example, of ancient Greece and Rome? Well, he
concluded, they are reduced to the status of ordinary human beings, no longer
with the perquisites and powers of the godhead. They must now work for a living– like everyone else. He perceived that they might be somewhat secretive about
their diminished circumstances, but would at times complain about having to domenial labor when once they supped at Olympus. Such retired deities, hereasoned, would be thrown into insane asylums. Therefore, the most reasonable
method of locating these defrocked gods was to incarcerate himself in the local
mental institution – which he promptly did.
While we may disagree with some of the steps in his reasoning, we probably all
agree that the gentleman did the right thing.
My informant decided that to search for all the ancient and legendary gods ofold would be too tiring a task. Instead, he set his sights on only a few: Jupiter,
Mercury, and the goddess on the obverse face of the old British penny – noteveryone's first choice of the most interesting gods, but surely a representative trio.
To his (and my) astonishment, he found – incarcerated in the very asylum inwhich he had committed himself – Jupiter, Mercury, and the goddess on the
obverse face of the old English penny. These gods readily admitted their identities
and regaled him with stories of the days of yore when nectar and ambrosia flowed
freely.
And then my correspondent succeeded beyond his hopes. One day, over abowl of Bing cherries, he encountered "God Almighty," or at least a facsimile
thereof. At least the Personage who offered him the Bing cherries modestly
acknowledged being God Almighty. God Almighty luckily had a small spaceshipon the grounds of the asylum and offered to take my informant on a short tool
around the Solar System – which was no sooner said than done.
"And this, Dr. Sagan, is how I can assure you that the planets are inhabited."
The letter then concluded something as follows: "But all this business about life
elsewhere is so much speculation and not worth the really serious interest of ascientist such as yourself. Why don't you address yourself to a really important

problem, such as the construction of a trans-Canadian railroad at high northernlatitudes?" There followed a detailed sketch of the proposed railway route and astandard expression of the sincerity of his good wishes.
Other than stating my serious intent to work on a trans-Canadian railroad at
high northern latitudes, I have never been able to think of an appropriate responseto this letter.

Chapter 12: The Venus Detective Story
One of the reasons that planetary astronomy is such a delight these days is that it
is possible to find out what's really right. In the old days, you could make any
guess you liked, however improbable, about a planetary environment, and there
was little chance that anyone could ever prove you wrong. Today, spacecraft hang
like swords of Damocles over each hypothesis spun by planetary theoreticians, andthe theoreticians can be observed in a curious amalgam of hope and fear as eachnew burst of spacecraft planetary information comes winging in.
Back when astronomers had telescopes, eyeballs, and very little else to assist
their observations, Venus beckoned as a sister world. By the late nineteenth
century, it was known that Venus had about the same mass and radius as Earth.
Venus is the closest planet to Earth, and it was natural to assume that it was, inother respects, Earth-like.
Immanuel Kant imagined a race of amorous quasi-humans on Venus. EmanuelSwedenborg and Annie Besant, a founder of theosophy, found – by methods
described as spirit travel and astral projection – creatures very like humans on
Venus. In more recent years, some of the more spectacularly audacious flyingsaucer accounts – for example, those of George Adamski – populated Venus witha race of benign and powerful beings, many of whom seem to have been garbed inlong hair and long white robes – clear symbolism, in pre-1963 America, of deep
spiritual intent. There is a long history of wishful thinking, bemused speculation,and conscious and unconscious fraud, which produced a popular expectation that
our nearest planetary neighbor is habitable by humans, and is possibly even alreadyinhabited by creatures rather like us.
It was, therefore, with a sense of considerable surprise, and even annoyance,that the results of the first radio observations of Venus were greeted. These
measurements, performed in 1956 by C. H. Mayer and colleagues at the U. S.
Naval Research Laboratory, found Venus to be a much more intense source ofradio emission than had been expected. From Venus' distance to the Sun and theamount of sunlight it reflects back to space, the planet should be cool. Because
Venus reflects so much sunlight back to space, its temperature ought to be evenless than the Earth's, despite its closeness to the Sun. Mayer's group found that
Venus, at a radio wavelength of 3 centimeters, was giving off as much radiation as
it would if it were a hot body at a temperature of about 600 degrees Fahrenheit.
Later observations with many different radio telescopes at many different radio
frequencies confirmed the general conclusion that Venus had a "brightness
temperature" of about 600 degrees to 800 degrees.

Nevertheless, there was great reluctance in the scientific community to believethat the radio emission came from the Venus surface. A hot object emits radiation
at many wavelengths. Why did Venus seem hot only at radio wavelengths? How
could the surface of Venus be kept so hot? And finally – since psychologicalfactors may be unconsciously compelling, even in science – a Venus hotter thanthe hottest household oven is simply less pleasant a prospect than the Venus
populated, in the long tradition from Kant to Adamski, by gracious humans ofamorous or spiritual inclinations.
This problem of the origin of the Venus radio emission was a major part of my
doctoral dissertation. I wrote some twenty scientific papers concerning it between
1961 and 1968, when the problem was finally considered settled. I look back on
this period with pleasure. The Venus radio story is very much like a detective
story where there are clues littering the pages. Some are vital to the solution;others are false clues, leading in the wrong direction. Sometimes the right answer
can be deduced by bearing in mind all the relevant facts and requiring reasonable
logical consistency and plausibility.
There were several things we knew about Venus. We knew how thebrightness temperature varied with radio frequency. We knew how Venus
reflected back to Earth radio waves sent out by large radar telescopes. Man's firstsuccessful planetary probe – the United States' Mariner 2 – found in 1962 that
Venus was brighter at radio wavelengths at its center than at its edge.
To be matched against such observations were a variety of theories. They fell
into two general categories: The hot-surface model, in which the radio emission
came from the solid surface of the planet; and the cold-surface model, in which
the radio emission came from somewhere else – from an ionized layer in theatmosphere of Venus, or from electrical discharges between droplets in the cloudsof Venus, or from a hypothesized great belt of rapidly moving electrically charged
particles surrounding Venus (like those that, in fact, surround the Earth andJupiter). These latter models permitted the surface to be cold by placing theintense radio emission above the surface. If you wanted sailing ships on Venus,
you were a cold-surface model advocate.
We systematically compared the cold-surface models with the observations
and found that they all ran into serious troubles. The model in which the radio
emission came from the ionosphere, for example, predicted that Venus should notreflect radio waves at all. But radar telescopes had found radio waves reflectedfrom Venus with an efficiency of 10 or 20 percent. To circumvent suchdifficulties, advocates of the ionospheric model constructed very elaboratehypotheses in which there were many ionized layers with especially constructed
holes in them to let radar through the ionosphere, hit the surface of Venus, andreturn to Earth. At the same time there could not be too many holes; otherwise,
the radio emission would not be as intense as observed. These models seemed to
me to be far too detailed and arbitrary in their requirements.
Just before the remarkable spacecraft observations of Venus of 1968, I
submitted a paper to Nature, the British scientific journal, in which I summarizedthese conclusions and deduced that only the hot-surface model was consistent
with all the evidence. I had earlier proposed a specific theory, in terms of thegreenhouse effect, to explain how the surface of Venus could be at such hightemperatures. But my conclusions against cold-surface models in 1968 did notdepend upon the validity of the greenhouse explanation: It was just that a hot
surface explained the data and a cold surface did not. Because of my interest in
exobiology, I would have preferred a habitable Venus, but the facts led elsewhere.
In a paper published in 1962, I had concluded from indirect evidence that the
average surface temperature on Venus was about 800 degrees F and the averagesurface atmospheric pressure about fifty times larger than at the surface of Earth.
In 1968, an American spacecraft, Mariner 5, flew by Venus, and a Soviet
spacecraft, Venera 4, entered its atmosphere. By the year 1974 there had been five
Soviet instrumented capsules that entered the Venus atmosphere. The last three
touched down and returned data from the planetary surface. They were the firstcraft of mankind to land on the surface of another planet. The averagetemperature on Venus turns out to be about 900 degrees F; the average pressure
at the surface appears to be about ninety atmospheres. My early conclusions wereapproximately correct, just slightly too conservative.
It is interesting, now that we know by direct measurements the actual
conditions on Venus, to read some of the criticism of the hot-surface model
published in the 1960s. The year after receiving my Ph.D., I was offered, by a wellknown planetary astronomer, ten-to-one odds that the surface pressure on Venus
was no more than ten times that on Earth. I gladly offered my ten dollars against
his hundred; to his credit, he paid off – after the Soviet landing observations werein hand.
Theory and spacecraft interact in other ways. For example, Venera 4 radioed its
last temperature/pressure point at 450 degrees F and twenty atmospheres. The
Soviet scientists concluded that these were the surface conditions on Venus. But
ground-based radio data had already shown that the surface temperature must be
much higher. Combining radar with Mariner 5 data, we knew that the surface ofVenus was far below where the Soviet scientists concluded Venera 4 had landed.
It now appears that the designers of the first Venera spacecraft, believing themodels of cold-surface theoreticians, built a relatively fragile spacecraft, which was
crushed by the weight of the Venus atmosphere far above the surface – much as asubmarine, not designed for great depths, will be crushed at the ocean bottoms.
At the 1968 Tokyo meeting of COSPAR, the Committee on Space Research of
the International Council of Scientific Unions, I proposed that the Venera 4
spacecraft had ceased operating some fifteen miles above the surface. My
colleague, Professor A. D. Kuzmin, of the Lebedev Physical Institute, in Moscow,
argued that it had landed on the surface. When I noted that the radio and radar
data did not put the surface at the altitude deduced for the Venera 4 touchdown,
Dr. Kuzmin proposed that Venera 4 had landed atop a high mountain. I argued
that ground-based radar studies of Venus had shown mountains a mile high, at
most, and that it was exceptionally unlikely Venera 4 would land on the only
fifteen-mile-high mountain on Venus, even if such a mountain were possible.
Professor Kuzmin replied by asking me what I thought was the probability thatthe first German bomb to fall on Leningrad in World War II would kill the only
elephant in the Leningrad zoo. I admitted that the chance was very small, indeed.
He responded, triumphantly, with the information that such was indeed the fateof the Leningrad elephant.
The designers of subsequent Soviet entry probes were, despite the Leningrad
zoo, cautious enough to increase the structural strength of the spacecraft in eachsuccessive mission. Venera 7 was able to withstand pressures of 180 times that at
the surface of the Earth, a quite adequate margin for the actual Venus surface
conditions. It transmitted twenty minutes' worth of data from the Venus surface
before being fried. Venera 8, in 1972, transmitted more than twice as long. The
surface pressure is not at twenty atmospheres, and the spectacular Mount Kuzmin
does not exist.
The principal conclusion about the scientific method that I draw from thishistory is this: While theory is useful in the design of experiments, only direct
experiments will convince everyone. Based only on my indirect conclusions, there
would today still be many people who did not believe in a hot Venus. As a resultof the Venera observations, everyone acknowledges a Venus of crushing pressures,
stifling heat, dim illumination, and strange optical effects.
That our sister planet should be so different from Earth is a major scientificproblem, and studies of Venus are of the greatest interest in understanding theearliest history of Earth. In addition, it helps to calibrate the reliability of astralprojection and spirit travel of the sorts popularized by Emanuel Swedenborg,
Annie Besant, and innumerable present-day imitators, none of whom caught a
glimmering of the true nature of Venus.

Chapter 13: Venus Is HellThe planet Venus floats, serene and lovely, in the sky of Earth, a bright pinpointof yellowish-white light. Seen or photographed through a telescope, a featurelessdisc is discerned; a vast unbroken and enigmatic cloud layer shields the surface
from our view. No human eye has seen the ground of our nearest planetaryneighbor.
But we now know a great deal about Venus. From radio telescope and spacevehicle observations, we know that the surface temperature is about 900 degrees
Fahrenheit. The atmospheric pressure at the surface of Venus is about ninety
times that which we experience at the surface of the Earth. Since the planet's
gravity is about as strong as the Earth's, there are about ninety times more
molecules in the atmosphere of Venus as in the atmosphere of Earth. This dense
atmosphere acts as a kind of insulating blanket, keeping the surface hot throughthe greenhouse effect and smoothing out temperature differences from place toplace. The pole of Venus is probably not significantly colder than its equator, andon Venus it is as hot at midnight as at noon.
Forty miles above the surface is the thick cloud layer that we see from Earth.
At least until recently, no one knew the composition of these clouds. I had
proposed that they were constituted in part of water, a cosmically very abundantmaterial, which could account for many but by no means all of the observed
properties of the Venus clouds. But there were many other candidate materials
proposed, among them, ammonium chloride, carbon suboxide, various silicatesand oxides, solutions of hydrochloric acid, a hydrated ferric chloride,
carbohydrates, and hydrocarbons. These last two materials were proposed by
Immanuel Velikovsky in his speculative romance Worlds in Collision to provide
manna for the Israelites during their forty years of wandering in the desert. The
other candidate materials were proposed on somewhat firmer grounds. Yet each ofthem ran afoul of one or more of the observations.
But recently a material has been proposed that is in excellent quantitative
agreement with all of the measurements. The American astronomer Andrew T.
Young has shown that the clouds of Venus are very likely a concentrated solutionof sulfuric acid. A 75 percent solution of H2SO4 precisely matches the index ofrefraction of the Venus clouds determined by polarimetric observations from the
Earth. None of the other materials comes close. Such a solution is liquid at thetemperatures and pressures at which the Venus clouds reside. Sulfuric acid has anabsorption feature, determined by infrared spectroscopy, at a wavelength of 11.2
microns. Of all the materials proposed, only H2SO4 has such an absorption feature.

The Soviet entry spacecraft of the Venera series have found large quantities ofwater vapor below the visible clouds of Venus. Ground-based observers looking
for water vapor spectroscopically have found only a tiny amount of water vapor
above the clouds of Venus. The two observations are in accord only if a very
effective drying agent is present between these two regions. Sulfuric acid is suchan agent.
In the Earth's atmosphere there are water droplets at altitude, and water vapor
in the atmosphere below. Likewise on Venus: If there are sulfuric acid droplets in
the high clouds, there must be gaseous sulfuric acid below, with a relatively highconcentration near the surface. Astronomers in Earth-bound observatories havealso found unmistakable evidence of hydrochloric acid and hydrofluoric acid asgases in the upper atmosphere of Venus. They also must exist in a fairconcentration – for example, the relative proportions of Los Angeles smog in Los
Angeles air – in the lower atmosphere of Venus. These three acids are an
extremely corrosive mixture. Any spacecraft that is to survive on the Venus
surface must not only be bulwarked against the high pressures but protectedagainst the corrosive atmosphere.
The Soviet Union is engaged in a very active program of unmanned explorationof Venus. We now know there is enough light for photography at midday on the
Venus surface. The time will come, in not too many years, I think, when we will
have our first photographs of the surface of Venus. What does the surface ofVenus look like? To some extent we can already make predictions.
Because of the very dense atmosphere of Venus, there are some interesting
optical effects. The most important such effect is due to Rayleigh scattering,
named after the British Lord Rayleigh. When sunlight strikes the clear, dust-freeatmosphere of the Earth, it is scattered. Photons strike the molecules of the Earth's
atmosphere and are bounced off. Many such bounces may occur. But because themolecules of air are very much smaller than the wavelength of light, it turns outthat short wavelengths are scattered or bounced away by the air molecules more
efficiently than long wavelengths. Blue light is scattered much better than red
light. This was a fact known to Leonardo da Vinci, who painted distant landscapesin an exquisite cerulean blue. It is why we talk of purple mountains; it is why thesky is blue. The light from the sun is scattered about in our atmosphere – some ofit being scattered up and out again, but other fractions of sunlight being scatteredabout by the molecules of our atmosphere and then, from quite a different
direction than that of the Sun, scattered back down to our eyeballs. In the absenceof an atmosphere, as on the Moon, the sky is black. When we look at a sunset weare seeing the Sun through a longer path in the Earth's atmosphere than when weview it at noon. Blue light has been preferentially scattered out of this path,leaving only the red light to strike our eyes. The beauty of the sunset, the sky, anddistant landscapes are all due to Rayleigh scattering.
What about Rayleigh scattering on Venus? Because the atmosphere is so muchdenser, Rayleigh scattering there is much more important. Were we to strip theclouds off Venus, we would still be unable to see its surface from above. Visible
light of all colors would be scattered so many times in the Venus atmosphere thatno image of any surface details would be discerned. In the near infrared, atwavelengths longer than the human eye is sensitive to, the surface could, however,be seen from above. But there are clouds. Radio waves penetrate the clouds andthe atmosphere of Venus and the first radar maps of Venus are being developed(see page 80). In a few years, Cornell University's great Arecibo telescope in
Puerto Rico will begin mapping the surface of Venus by radar with higher
precision than the best ground-based optical maps of the Moon. Already, there arehints of mountain ranges and great impact basins on the surface of this enigmatic
planet.
At the surface of Venus, Rayleigh scattering is also an extremely important
effect. Just as we cannot see the surface in visible light from above Venus, wecannot see the sun in visible light from the surface of Venus – even if there were abreak in the clouds. If there were intelligent life on Venus, astronomy would bevery slow to develop; and radio astronomy would emerge first. The Venera 8
spacecraft found that sunlight does reach the surface of Venus during the day, but
it is so attenuated by passage through the clouds and atmosphere that, even at
midday, it is no brighter on Venus than at twilight on the Earth. The sunlightwould be a hazy and diffuse patch of deep ruby-red light, whose rising and setting
could only indistinctly be determined.
If you were standing in some protective suit on the surface of Venus and put
on violet sunglasses, you would see no farther than a few dozen feet. The Rayleighscattering in blue light is so strong on Venus that the visibility in the violet issmall. But because long wavelength light is scattered less than blue, at the extreme
red end of the visible spectrum – with red sunglasses on – you could see perhaps athousand feet. At the surface of Venus everything would be suffused in a deep red
gloom. We would have a perception of color, but only for objects very close to us.
Our surroundings would be an indistinct roseate blur.
Venus thus seems to be a place quite different from the Earth, and alarmingly
unappealing: Broiling temperatures, crushing pressures, noxious and corrosive
gases, sulfurous smells, and a landscape immersed in a ruddy gloom.

Curiously enough, there is a place astonishingly like this in the superstition,
folklore and legends of men. We call it Hell. In the older belief – that of the
Greeks, for example – it was the place where all human souls journeyed after
death. In Christian times it has been thought of as the post-mortem destination
only of one of two categories of moral persuasion. But there is little doubt that the
average person's view of Hell – sizzling, choking, sulfurous, and red – is a deadringer for the surface of Venus.
Although terrestrial biological molecules would fall to pieces rapidly on Venus,
there are organic molecules – for example, some with a complex ring structure –that would be quite stable under the conditions of Venus. It is difficult to exclude
life there, but we can certainly say it would be quite different from what we arefamiliar with. Any organism that lives there would be wise to have leathery skin.
Because of the high atmospheric pressures, it would even make sense to have little
stubby wings, which could carry their possessors about without exceptionallystrenuous flapping. A devil is a very good model – except for his mannish andgoaty aspects – for an inhabitant of Venus. Milton and Isaiah called Lucifer "Son of
the Morning," the morning star. For thousands of years Venus and Hell have been
identified.
This is all a very curious coincidence, but I cannot bring myself to think that it
is anything more than that. The chief point is that in all the legends one gets toHell by going down, not up. The classical world of Greece and Rome and theancient Near East were peppered with active volcanoes. Such volcanic terrains,
like in contemporary Iceland and Hawaii, are bleak, desolate, and eerily beautiful
landscapes. Sulfurous gases emanate from volcanic vents; lava fountains and flows
suffuse the surroundings in red. It is very hot: You singe your eyebrows if you get
too close to the lava in a collapsed lava tube. And all this heat, redness, and smell
come from down below. It was not very difficult for our ancestors to imagine that
volcanic terrains were apertures to a quite different igneous world called Hell.
The inside of the Earth and the outside of Venus are alike but not identical.
They are both unpleasant for humans. But they are both of extreme scientificinterest – worth at least an extended visitation, if not a homesteading. Dante knew
about that.

Chapter 14: Science and "Intelligence"
I spent my first two postdoctoral years at the University of California, Berkeley,
where, among other things, I was concerned with searching for life elsewhere andwith the sterilization of space vehicles intended for places like Mars – we wished
not to contaminate the Martian environment with microbes from Earth.
One bright spring day I received a phone call from an Air Force general whom
I had met at several scientific meetings. He had been working chiefly on aviation
medicine; I will call him here Bart Doppelganger. General Doppelganger informedme that he was in Los Angeles with three Soviet scientists, one of whom was incharge of the Soviet effort for constructing instruments to search forextraterrestrial life. His name was Alexander Alexandrovitch Imshenetsky (there
is no reason to change his name; unlike some others in this narrative he has
nothing to be ashamed of). It was Imshenetsky's first visit to the United States.
Yes, I would certainly be interested in meeting him. When? The answer was"immediately." So I drove to San Francisco airport, flew to Los Angeles, and took ataxi to an address given to me by our General Doppelganger.
It was the home of a professionally well-known UCLA brain physiologist. In
the living room, upon my arrival, were the physiologist, other aviation medicine
experts from UCLA, General Doppelganger, three Soviet scientists (two inaviation medicine and Academician Imshenetsky), and a translator. I will call thetranslator Igor Rogovin; he was an American employee of the Library of Congressassigned to do translation for the three Russians on their visit to the United States.
The only thing that struck me as somewhat peculiar was that the English of all
three Russians was quite good. So why a translator?
Everyone was jolly, pleasantries were exchanged, drinks made the rounds – andIgor Rogovin also made the rounds. There was no conversation from which he wasabsent for more than a few minutes. He was very busy, like a manic bee
obsessively flitting from flower to flower.
After a while, the plan was for all of us to drive to Los Angeles International
Airport, where the Russians were later to catch a plane. Before their flight, wewere all to have dinner. There were more of us than could fit into one car, andRogovin could not easily ride in both cars at once. Imshenetsky, some others, and I
rode in one car, and Rogovin and the others in a second. During the twenty- or
thirty-minute drive, Imshenetsky and I had a fruitful exchange of views on
methods of life detection and space-vehicle sterilization technology. It was the firstsuch contact I had had with a Soviet scientist.

We arrived at the airport, bags were checked, and the Soviets excused
themselves to go to the men's room. Waiting outside, I found myself alone with
Igor Rogovin – who immediately said to me out of the corner of his mouth, and ina style of vocalization that went out with James Cagney and Humphrey Bogart,"Hey, kid, what'd ya find out?"
Being unwise in the ways of the world, and pleased with the information
Imshenetsky and I had exchanged, I rapidly summarized what I had learned.
"Pretty good, kid. Who do you work for?""The University of California at Berkeley," I replied brightly.
"No, no, kid, not the cover."Igor Rogovin's occupation, if not his identity, gradually dawned on me. With arising fury I explained to him that it was possible to have a conversation with a
Soviet scientist that was intended for the benefit of science rather than for the
benefit of American military intelligence services. Before Rogovin could reply, ourfriendly Soviet guests re-emerged, and we all went off to dinner.
Although seated again next to Imshenetsky, I found myself unable to talk tohim on any subject remotely approaching science. As I recall, our primary topics
of conversation were American films and Soviet poets. After a number of drinks,
Alexander Alexandrovitch Imshenetsky offered the opinions that William
Shakespeare was the leading Russian poet and American cowboy films were
excessively violent. Several hours easily could be spent discussing these two
propositions. As the Russians left to fly home, I returned to Berkeley.
The next morning, I turned to the white pages of the San Francisco telephone
directory and, under "United States Government," found a section marked"Central Intelligence Agency." On dialing the number indicated I encountered acheerful voice that said something like "Yukon 4-2143.""Hello, Central Intelligence Agency?" I said.
"What can we do for you, sir?""I have a complaint to file.""One moment, sir, I will give you our Complaint Department." This was
shortly after the Bay of Pigs, and I guess they had been getting a lot of complaints.
Upon reaching – yes – the Complaint Department, I rapidly launched into a
synopsis of my encounter with Mr. Rogovin, but was quickly silenced with an
injunction that this was not the sort of thing one talked about over the telephone.
I suppose his phone was tapped. We made an appointment for later that afternoon
in my office.

Sure enough, at the prescribed time, two neatly dressed business-suited young
men arrived, bearing plastic identification cards with the signature of John
McCone, who had recently been appointed Director of the Central Intelligence
Agency. After expressing my general annoyance by an exceptionally long scrutinyof their IDs, I launched into my story. In their faces was mounting concern. At theconclusion of my narrative, they explained to me that Rogovin's behavior was very
unlikely to be the behavior of any employee of "the agency." They were very
concerned about such a story, particularly after the "bad press" they had beengetting about the Bay of Pigs. They would do everything to track the story down if
I would not embarrass the agency by further disseminating the story. I agreed tokeep quiet, for a while, and they departed.
About a week later I received a phone call: "Dr. Sagan, this is Mr. Smith, who
was in your office last week. You recall the matter about which we talked?" Igathered that his phone was still tapped.
"We have been able to establish that the party in question – you know who I
mean? – does not work for our organization under that name. We are, of course,
pursuing other names and will get back to you as soon as we can."It had taken them a week to scrutinize the personnel roster of the Central
Intelligence Agency. The roster must either be very long or very secret.
Several days later, in similarly veiled language, I was called and told – in a voicethat seemed to express considerable concern – that Igor Rogovin did not work for
the CIA under any name whatever, and that they were, under the circumstances,
naturally curious to know for whom he did work.
After another week had passed, the CIA made an appointment to speak withme once again in my office. The same two gentlemen arrived, again bearing thesame two plastic cards signed by John McCone. They informed me that, after
exhaustive investigations, they had discovered that Igor Rogovin, while nominallyworking for the Library of Congress, was, in fact, an employee of Air ForceIntelligence. They again assured me that no representative of their agency would
ever behave in so uncouth a manner, and departed. What stood out most clearly
was that it had taken about two weeks for the Central Intelligence Agency todetermine the employment of a member of a fellow U.S. intelligence organization.
This story has a coda. A year or two later the international space organization,
COSPAR, was meeting in Florence, Italy. In one of the splendid side benefits ofsuch meetings, the Uffizi Gallery was opened one evening especially for themembers of the COSPAR delegations from various nations. As chance would haveit, I was with Alexander Alexandrovitch Imshenetsky as we entered an enormousand apparently empty Botticelli-inundated gallery. And there, at the other end of
the gallery, a human figure could dimly be perceived. I felt Imshenetsky stiffen.
Peering intently, I could now make out the visage of Igor Rogovin, his facedisguised by a beard. He was, no doubt, traveling incognito. Imshenetsky leaned
over to me and whispered, "Isn't that the fellow who was with us in Los Angeles?"When I nodded assent, Imshenetsky murmured, "Very stupid fellow."That Rogovin was working for Air Force Intelligence is, in retrospect, not sosurprising, since I had been invited to Los Angeles by General Doppelganger. That
Soviet plans for the search for life elsewhere or for the sterilization of spacecraft
could be considered of interest to Air Force Intelligence is perhaps more
surprising. That American intelligence agencies would attempt to use
comparatively innocent young scientists (I was twenty-seven and politicallyunsophisticated) to carry out such a purpose is appalling. At least it appalls me.
There are many other such stories involving both American and Soviet
intelligence organizations. The general effect of such incidents is to detract fromthe credibility of legitimate scientific exchanges among scientists of different
countries. Such exchanges are particularly necessary in an age that hangs a thread
away from nuclear destruction, and in which scientists have access to at least half
an ear of the politicians in power. The fact that such intelligence activities arepracticed in an entirely regular and invariable manner on the Soviet side does not,in my view, weaken this argument. The intrusion of "intelligence" into
international scientific exchanges of this sort is, whatever else it is, just not
intelligent.

Chapter 15: The Moons of Barsoom
In my boyhood I was lucky enough to come upon a set of turgidly written novels
with names like Thuvia, Maid of Mars, The Chessman of Mars, The Princess ofMars, The Warlords of Mars, and so on. They were, needless to say, about Mars.
But they were not about our Mars – the Mars revealed by Mariner 9.
At least I don't think our Mars is like the Mars of these novels by Edgar Rice
Burroughs, the inventor of Tarzan. His Mars was Percival Lowell's Mars – a planetof ancient sea bottoms, working canals and pumping stations, six-legged beasts ofburden, and men (some headless) of all colors, including green. They had names
like Tars Tarkas. Possibly the most remarkable hypothesis proposed by Burroughsin these novels was that human beings and inhabitants of Mars could produce live
offspring – a biologically impossible proposition if the Martians and we are
imagined as having separate biological origins. Burroughs wrote decorously of theinterfertility of a Virginian miraculously transported to Mars and Dejah Thoris, theprincess of a kingdom with the improbable name of Helium. I have little doubtthat the precedent of a kingdom called Helium led directly to the planet called
Krypton, home of the comic-book hero Superman. There is here a rich vein of
untapped literary ore. The future may hold planets, stars, or even entire galaxies
named Neon, Argon, Xenon, and Radon – the remaining noble gases.
But the name invented by Burroughs that has haunted me across the years isthe name he imagined the Martians gave to Mars: Barsoom. And it was one phraseof his more than any other that captured my imagination: "The hurtling moons of
Barsoom."
For Mars is indeed a world with two moons – a situation that would appear to
the inhabitants of Mars as entirely natural as our one Moon does to us. We knowhow our solitary satellite looks to the naked eye from the surface of Earth. But
what do the moons of Barsoom look like from the surface of Mars? This question,
which intermittently plagued my boyhood, was not to be answered until 1971 andMariner 9.
The moons of Mars were invented by Johannes Kepler, the discoverer of thelaws of planetary motion and no intellectual lightweight. But he lived in thesixteenth century, in a different intellectual climate from the present. He casthoroscopes for a living; astronomy was his passion more than his occupation. His
mother was tried as a witch. When Kepler learned of Galileo's discovery, with oneof the first astronomical telescopes, of the four large moons of Jupiter, he
immediately concluded that Mars had two moons. Why? Because Mars was at anintermediate distance from the Sun, between Earth and Jupiter. It must obviously
have an intermediate number of moons. The observations seemed to show Venus
with no moons, Earth with one, and Jupiter with four (the actual number, we
now know, is twelve). Kepler could have deduced either two or three moons forMars. But bearing a lifelong passion for geometrical progressions, he chose two.
The argument is, of course, fallacious. Saturn's ten moons, Uranus' five, and
Neptune's two in no way fit his scheme, which is not scientific but aesthetic.
But Kepler's prestige was immense, particularly after Kepler's laws of planetary
motion were derived from gravitational theory by Isaac Newton; and so, literary
allusions to the two moons of Mars fluttered down the centuries. In Voltaire's
longish short story "Micromegas" a denizen of the star Sirius notes casually, while
touring our Solar System, that Mars had two moons. There is a more famousreference to two Martian moons in Jonathan Swift's satire of 1726, Gulliver's
Travels – not the part about the very small people, or the part about the very large
people, or the part about the intelligent horses, but a less widely read part – thepart about the floating aerial island of Laputa. The episode is undoubtedly a tightly
reasoned critique of English-Spanish relations in Swift's time, because la puta is
Spanish for prostitute. The political metaphors are obscure, at least to me. At any
rate, Swift announces casually that astronomers on Laputa have discovered two
swiftly moving moons of Mars, and have provided information on their distancesfrom Mars and their periods of revolution about Mars – information that isincorrect, but that is not a bad guess. There is an entire genre of writing on how it
was that Swift knew about the moons of Mars, including the suggestion that he
was a Martian. Internal evidence suggests that Swift was no Martian, and the twomoons can almost certainly be traced directly back to Kepler's speculations.
The actual discovery of the moons of Mars was made from outside
Washington, D.C., in 1877. The U. S. Naval Observatory had just completed alarge refracting telescope. The observatory's astronomer, Asaph Hall, sought tolearn whether the moons of Mars, fabled in song and story, actually existed. His
first few nights were unsuccessful, and, in a despondent mood, he announced to
his wife his intention of quitting the search. Mrs. Hall would have none of this,and urged her reluctant husband back to a few more nights at the telescope –whence he emerged with two Martian satellites in hand. For a brief period hethought he had found three satellites, because the inner one moved so rapidly thaton one night he saw it on one side of Mars and on the next night on the other.
Hall named the moons Phobos and Deimos, after the horses that pulled thechariot of the god of war in Greek mythology; they have the cheerful denotationsof fear and terror, respectively. (The appropriate adjectives pose some problems:
Do we talk of Phobic orbits and Deimonic nights?) If another moon of Mars issomeday found, I hope we will give it a less ferocious and more optimistic name –like "Pax."
I also hope that when the features on Phobos and Deimos are eventually
named by the International Astronomical Union, one will be named after Mrs.
Hall. But since another feature will surely be named after Asaph Hall, we have aproblem – two craters named Hall would be confusing. In an astronomy talk I
gave at Harvard University, I commented wistfully that the problem would be
solved if only we knew Mrs. Hall's maiden name. My friend Owen Gingerich,
Professor of the History of Science at Harvard, instantly leaped to his feet with thewords "Angelina Stickney" tripping off his lips. So when the time comes, I hope
there will be a "Stickney" on one of the moons of Barsoom.
The subsequent study of Phobos and Deimos between 1877 and 1971 has acurious history. The moons of Mars are so tiny that they appear, even to thelargest Earthbound telescopes, as dim points of light. They are too faint for the
pre-1877 telescopes to have seen them at all. Their orbits can be calculated bynoting their positions at various times. In 1944 at the U. S. Naval Observatory(where an understandably proprietary interest in Phobos and Deimos must havedeveloped), B. P. Sharpless collected all the observations available in his day todetermine the orbits to the best possible precision. He found – no doubt to his
surprise – that the orbit of Phobos appeared to be decaying, what astronomers calla secular acceleration. Over longish periods of time the satellite seemed to beapproaching more and more closely to Mars and moving more and more rapidly.
This phenomenon is quite familiar to us today. The orbits of artificial satellites aredecaying all the time in the Earth's atmosphere. They are initially slowed bycollisions with the diffuse upper atmosphere of the Earth, but by Kepler's laws the
net result is a more rapid motion.
Sharpless' conclusion of a secular acceleration for Phobos remained an
unexplained and almost unexamined curiosity until it was considered around 1960
by the Soviet astrophysicist I. S. Shklovskii. Shklovskii considered a wide range ofalternative hypotheses for the secular acceleration, among them the influence of
the Sun, the influence of a hypothetical magnetic field on Mars, and the tidal
influence of the gravity of Mars. He found that none of these came close toworking. He then reconsidered the possibility of atmospheric drag. The exact sizeof the Martian satellites was known poorly and indirectly in those days before
spacecraft investigation of Mars, but it was known that Phobos was roughly ten
miles in diameter. The altitude of Phobos above the surface of Mars was also
known. Shklovskii and others before him found that the density of the atmosphere
was far too low to produce the drag that Sharpless had deduced. It was at thispoint that Shklovskii made a brilliant and daring guess.

All the calculations showing atmospheric drag to be ineffectual had assumed
that Phobos was an object of ordinary density. But what if its density were very
low? Despite its enormous size, its mass would then be quite small, and its orbit
could be appropriately affected by the thin upper atmosphere of Mars.
Shklovskii calculated the required density of Phobos, and found a value about
one one-thousandth the density of water. There is no natural object or substancewith such low density; balsa wood, for example, has about half the density ofwater. With such a low density, there was only one conclusion possible: Phobos
had to be hollow. A vast hollow object ten miles across could not have arisen by
natural processes. Shklovskii, therefore, concluded that it was produced by anadvanced Martian civilization. Indeed, an artificial satellite ten miles acrossrequires a technology far in advance of our own; it would also be far in advance ofthe technology imagined on Barsoom by Burroughs, which was a kind of sword
and small spaceship technology.
Since there were no signs of such an advanced civilization on Mars today,
Shklovskii concluded that Phobos – and possibly Deimos – had been launched in
the distant past by a now extinct Martian civilization. (The interested reader may
find more details of this remarkable argument of Shklovskii's in the bookIntelligent Life in the Universe, jointly authored by Shklovskii and myself. [SanFrancisco, Holden-Day, 1966; New York, Delta Books, 1967]). Subsequent to
Shklovskii's first work on the subject, the motions of the moons of Mars were reexamined in England by G. A. Wilkins, who found that possibly there was nosecular acceleration. But he could not be sure.
Shklovskii's extraordinary suggestion that the moons of Mars might be artificial
is one of three hypotheses on their origin. The other two – certainly interesting intheir own right, but naturally paling in comparison with the Shklovskii hypothesis– are (1) that the moons are captured asteroids, or (2) that they are debris left overfrom the origin of Mars itself.
Asteroids are hunks of rock and metal that go around the Sun between theorbits of Mars and Jupiter. There are unlikely, but theoretically possible, scenarios
in which the gravitation of Mars can capture a close-passing asteroid.
In the Martian-debris hypothesis, it is imagined that pieces of rock of various
sizes fell together to form Mars; that the last generation of such infalling pieces
produced the large old impact craters on Mars (see page 131); and that Phobos andDeimos are by chance the only remnants still extant of the early catastrophic
history of Mars.

It is clear that establishing any one of these three hypotheses on the origin of
the moons of Mars would be a major scientific achievement.
The Mariner Mars mission of 1971, which I had the pleasure to work on, wasoriginally to have involved two spacecraft, Mariner 8 and Mariner 9. They were to
be placed in different orbits for different purposes in the study of Mars itself.
After these orbits were finally agreed upon, I noticed that they were not all thatfar from the orbits of Phobos and Deimos. It also seemed to me that television andother close-up observations of Phobos and Deimos by the Mariner spacecraft
might permit us to determine something of their origin and nature.
I therefore approached officials of NASA, which organized and ran the
mission, for permission to program observations of Phobos and Deimos. While themission controllers at Jet Propulsion Laboratory, the actual operating organization,
were not unsympathetic to this idea, some officials at NASA headquarters wereagainst it. There was a mission plan, written in a large book, which stated what
Mariners 8 and 9 were about. Nowhere in the mission plan were Phobos andDeimos mentioned. Ergo, I could not look at Phobos and Deimos.
I pointed out that my proposal required only moving the scan platforms on thespacecraft so that the cameras could observe the Martian satellites. The response
was negative again. A short time later, I advanced the argument that if Phobos andDeimos were indeed captured asteroids, examining them from Mariner 9 was theequivalent of a free mission to the asteroid belt: The proposed scan platformmaneuver would save NASA two hundred million dollars or so. This argument
was judged, at least in some circles, to be more compelling. After about a year of
my lobbying, a planning group on satellite astronomy was set up, and tentativeplans were made for examining Phobos and Deimos. The satellite astronomy
working group was, at my suggestion, chaired by Dr. James Pollack, a former
student of mine; but it was a sign of NASA reluctance that the group was formed
only after the launch of Mariner 9, and only about two months before its arrival at
Mars. (Mariner 8 had, meanwhile, failed.)
When Mariner 9 arrived at Mars, we found a planet almost entirely obscuredby dust. Since there was little to look at on Mars, a great and previously
undetectable enthusiasm for examining Phobos and Deimos dramaticallymaterialized. The first step was to take wide-angle photographs from a distance inorder to establish with some precision the orbits and locations of the moons. Thistask was accomplished in a preliminary way about two weeks after injection of
the spacecraft into Martian orbit. Mariner 9 has an orbital period of about twelve
hours, so that it made close to two revolutions around Mars per day.

The television pictures from Mariner 9 were radioed from Mars to Earth inmuch the same way that a newsprint wire-photo is transmitted on Earth. The
picture is divided into a large number of small dots (for Mariner 9, several
hundred thousand dots), each dot with its own brightness, or shade of gray,running from black to white. After the picture is taken by the spacecraft andrecorded there on magnetic tape, it is played back to Earth, dot by dot. The
communication says, in effect: Dot number 3277, gray level 65; dot number 3278,
gray level 62, and so on. The picture is reassembled by computer on the Earth –essentially by following the dots.
Late that same night, Dr. Joseph Veverka, of Cornell, another former studentof mine, and I worked into the small hours of the morning at the Image Processing
Laboratory of JPL to bring out – by computer contrast-enhancement techniques –all of the detail present in the image. The result is shown on page 102. The shape isirregular. Are those blotches craters?
Our computer-enhanced photograph was constructed on the computer's video
monitor, line by line, from top to bottom. As the apparent large crater at the top
gradually emerged, we saw a single bright spot at its center; for just a moment, I
had the sense that we were seeing a star through an enormous hole in Phobos – or,even more chilling, that we were seeing an artificial light. But when we requested
the computer to remove all single-bit errors, the bright spot went away.
On revolution 34, Mariner 9 and Phobos came within less than four thousand
miles of each other, one of the closest approaches in the entire mission. Late on
the night of the receipt of that picture, Veverka and I were again computerenhancing. I am not sure what an artificial satellite ten miles across looks like,but this does not seem to be it. Phobos looks not so much like an artificial satellite
as a diseased potato. It is, in fact, very heavily cratered. For it to have accumulated
so many craters in that part of the Solar System, it must be very old, probably billionsof years old.
Phobos appears to be an entirely natural fragment of a larger rock severely
battered by repeated collisions; holes have been dug, pieces have been chipped off.
It looks a little like the hand axes, chipped along natural fracture planes, made by
our Pleistocene ancestors. There is no sign of technology on it. Phobos is not an
artificial satellite. When pictures of Deimos were computer contrast-enhanced,
the same conclusion applied to it.
Phobos and Deimos are the first satellites of another planet to have beenphotographed close-up. They were also observed by the ultraviolet spectrometerand the infrared radiometer on board Mariner 9. We have been able to determine
their sizes and shapes and something of their color. They are extremely dark
objects – darker than the darkest material that is likely to be in the room in which
you are sitting right now.
Indeed, they are among the very darkest objects in the Solar System. Since
there are so few objects this dark anywhere, we hope to be able to conclude
something about their composition. They are both covered by at least thin layersof finely pulverized material. They provide important clues to collisional processes
in the early Solar System. I believe we are looking at the end-product of a kind ofcollisional natural selection, in which fragments have been broken off from a larger
parent body, and we are seeing only the two pieces, Phobos and Deimos, thatremain. The moons of Mars are also important collision calibrators for Mars.
Phobos, Deimos, and Mars have very likely been together in the same part of the
Solar System for a very long period of time. The number of craters of a given sizeon Mars is much less, in general, than on Phobos and Deimos, providing important
information on erosional processes that exist on Mars and that do not exist on
airless and waterless Phobos and Deimos.
Because we now have the first good information on the size and shape of theseobjects, and because we now have good reason to think that they have typicaldensities of ordinary rock, we can calculate something about what it would be liketo stand on, let's say, Phobos. First of all, Mars, less than six thousand miles away,
would fill about half the sky of Phobos. Marsrise would be a spectacular event.
Eventual construction of an observatory on Phobos to examine Mars might not besuch a bad idea. We know from Mariner 9 that both Phobos and Deimos arerotating as our Moon does, always keeping the same face to their planet. When
Phobos is above the day hemisphere of Mars, the reddish light of Mars would beenough to read by at night on Phobos.
Because of their small sizes, Phobos and Deimos have very low gravitational
accelerations. Their gravities do not pull very hard. The pull on Phobos is only
about one one-thousandth of that on Earth. If you can perform a standing highjump of two or three feet on Earth, you could perform a standing high jump ofhalf a mile on Phobos. It would not take many such jumps to circumnavigate
Phobos. They would be graceful, slow, arcing leaps, taking many minutes to reachthe high point of the self-propelled trajectory and then to return gently to theground.

Even more interesting would be a game like baseball on Phobos. The velocity
necessary to launch an object into orbit about Phobos is only about twenty miles
per hour. An amateur baseball pitcher could easily launch a baseball into orbit
around Phobos. The escape velocity from Phobos is only about thirty miles perhour, a speed easily reached by professional baseball pitchers. A baseball that had
escaped from Phobos would still be in orbit about Mars – a man-launchedmoonlet. If Phobos were perfectly spherical, a lonely astronaut with an interest in
baseball could invent a curious but somewhat sluggish version of this alreadyrather sluggish game. First, as pitcher, he could throw the ball sidearm – at thehorizon at between twenty and thirty miles per hour. He could then go home forlunch, because it will take about two hours for the baseball to circumnavigate
Phobos. After lunch, he can pick up a bat, face the other direction and await his
pitch of two hours earlier. Apart from the fact that good pitchers are seldom good
hitters, hitting this pitch would be pretty easy: About fifteen seconds elapse fromthe appearance of the baseball at the horizon to its arrival in the vicinity of ourastronaut. If he swings and misses – or, more likely, if the ball is wide of the plate– he can then go home for a two-hour nap, returning with his catcher's mitt tocatch the ball. Alternatively, if he succeeds in hitting a fly ball at a velocity
somewhere between twenty and thirty miles per hour, he can go home and takehis nap, returning this time with a fielder's mitt, awaiting the return of the ballfrom the opposite horizon two hours later. Because Phobos is gravitationally
lumpy, the game would be more difficult than I have indicated. Since daylight on
Phobos lasts only about four hours, lights would have to be erected, or the gamemodified so that all pitching, hitting, and catching events happen on the day side.
These sports possibilities may, one day a century or two hence, provide a
tourist industry for Phobos and Deimos. But baseball on Phobos is no more anargument for going there than, to take a random example, golf is for going to theMoon. The scientific interest in the moons of Mars – whether captured asteroids
or debris from the formation of the planet – is, however, immense. Sooner or later,
certainly on a time scale of centuries, there will be instruments – and then men –on the surface of Phobos looking up with awe at an immense red planet that fills
the sky from zenith to horizon.
And what about the opposite view? What do the moons of Barsoom look likefrom the surface of Mars? Because Phobos is so close to Mars, it would be seen as aclearly discernible disc, even though it is intrinsically such a tiny object. In fact,
Phobos would appear as about half the apparent size of our Moon seen from thesurface of Earth. We have found from Mariner 9 that only one side of Phobos isvisible from Mars, just as only one side of our Moon is visible from Earth. Thatface of Phobos is, more or less, the face on page 102. Until Mariner 9, no one –except Martians, if such there be – ever knew that face.

Because Phobos is so close to Mars, Kepler's laws constrain it to movecomparatively rapidly about the planet. It makes approximately 2½ revolutions
about Mars in 24 hours. Deimos, on the other hand, takes 30 hours 18 minutes torevolve in its orbit once about Mars. Both moons revolve in their orbits in thesame direction or sense as Mars rotates on its axis. Thus, Deimos rises in the eastand sets in the west as – from terrestrial chauvinism – we believe a well-behaved
satellite should. But Phobos makes it once around its orbit in less time than it
takes for Mars to rotate. Accordingly, Phobos rises in the west and sets in the east,
taking about 5½ hours to transit from horizon to horizon. This is not exactly"hurtling" – the motion would not be easily perceptible against the field of stars ina minute's watching – but it's not plodding, either. There will be some nights at
the equator on Mars when Phobos sets in the east at sunset and then rises in thewest well before dawn.
Phobos is so close to the equatorial plane of Mars that it is entirely invisible
from the polar regions of the planet. If we were to imagine intelligent beings
developing on Mars, astronomy might very well be the province of only theequatorial, and not the high-latitude, societies. I am not sure whether Helium wasan equatorial kingdom.
Freud says somewhere that the only happy men are those whose boyhood
dreams are realized. I cannot say that it has made my life carefree. But I will neverforget those early-morning hours in a chilly California November when Joe
Veverka, a JPL technician, and I were the first human beings ever to see the faceof Phobos.
The State of California was kind enough to give me an automobile license plate
marked "PHOBOS." My car is not particularly sluggish, but it cannot
circumnavigate our planet twice a day, either. The license plate pleases me. I
would have preferred "BARSOOM," but there is a strictly enforced limit of six
letters per license plate.

Chapter 16: The Mountains of Mars
I. Observations From Earth
The mountains of the Earth are the product of ages of geological catastrophes.
The major folded mountain ranges are thought to be produced by the collision ofenormous continental blocks during continental drift. The motion of continents
toward and away from each other, at a rate of about an inch a year, seems terribly
slow to us. But since the Earth is billions of years old, there has been plenty oftime for continents to bang around all over our planet.
Lesser mountains were produced by volcanic events. Hot molten rock, called
lava, upwells through tubes in the upper layers of the Earth – tubes of structural
weakness through which the underlying pressure is relieved – and produces large
surface piles of cooling volcanic slag. The resulting hole in the top of the volcanic
mountain – the geologists call it a summit caldera – is the channel through which
successive episodes of lava-upwelling occur. In the summit caldera of an active
volcano, as, for example, in Hawaii, we can actually see molten lava. These
individual volcanic mountains and mountain ranges, which are not really separate
entities, are signs of a geologically vigorous and dynamic Earth.
What about Mars? It is a smaller planet than Earth; its central pressures andtemperatures are less; it has a lower average density than Earth. These
circumstances combine to suggest that Mars should be geologically less active than
Earth, perhaps like the Moon. But even on the Moon, a much smaller object thanMars, with even lower anticipated interior temperatures than Mars, recent signs of
volcanic activity have been uncovered by the Apollo missions. We do not eventoday understand the connection between the size and structure of a planet andthe presence of volcanism and mountains, although we do know that there are no
significant folded mountain ranges on the Moon.
Our present ignorance on this subject is exceeded by the ignorance of the earlyplanetary astronomers, less than a century ago, as they peered through small
telescopes and tried to guess what distant Mars was like. One of the earliest
astronomers to commit himself on the question of mountains on Mars was
Percival Lowell. Lowell believed (see Chapter 18) that he had found evidence ofan extensive network of straight lines, crisscrossing the Martian surface withremarkable regularity and straightness, and that could only have been produced bya race of intelligent beings on that planet. He believed that these "canals" were
truly canals carrying water. We now know that the problem was not so muchwith his logic as with his observations; none of the Mariner or other recent

quantitative observations of Mars have shown any sign of the Lowellian canals.
In the 1890s Lowell argued that Mars must have no mountains, because
mountains would be a severe impediment to the construction of a comprehensive
network of canals. But surely a race that could construct a planet-wide network ofcanals should be able now and again to mow down an awkwardly placed
mountain.
Nevertheless, Lowell was among the very first astronomers to apply an actual
observational test to the question of mountains on Mars. He looked beyond theterminator. The terminator is the line – sharp or fuzzy, depending on the absenceor presence of a planetary atmosphere – that separates the day from the night sideof a planet. The terminator moves around the planet once a day – the local
planetary day. But if there are mountains just on the night side of the terminator,
the mountains will receive the rays of the setting Sun when their adjacent valleys
are in darkness. Galileo first used this technique to discover what he called themountains of the Moon – although the lunar mountains are mainly enormous
pieces of rubble that fell out of the sky in the final phases of the formation of theMoon, rather than mountains of the terrestrial type, produced by a geologically
active interior.
Lowell and his collaborators found cases of bright projections beyond theMartian terminator, illuminated by the rays of the setting Sun. But when theycalculated their altitudes – an easy task for anyone grounded in high schoolgeometry – the mountains were found to be many tens of miles high. Suchelevations on Mars seemed to him absurd because of his canal argument.
Moreover, the next day – the day on Mars is almost exactly the same length as a
day on Earth – when the feature was seen again, its position had changed. Thisbehavior is quite uncharacteristic of mountains of whatever origin, and Lowellcorrectly concluded that he had been seeing dust storms, in which fine particles
from the Martian surface had been carried some tens of miles into the Martian
atmosphere.
Such dust storms are also observed when we examine through the telescope
the day side of Mars. We sometimes see that the characteristic configuration ofbright and dark markings on the planet is temporarily obscured. There is anintrusion of bright-area material into the dark area, followed by a reappearance ofthe former configuration. These changes were interpreted in Lowell's time as dust
storms arising in the bright areas and obscuring the adjacent dark areas. The
present interpretation, based on the full range of Mariner 9 close-up observations,confirms this view (see Chapter 19).

Lowell and his contemporaries called the bright areas "deserts," and this, too,
seems to be an appropriate name. The Lowellians concerned themselves with the
problem of whether bright areas tended to be higher or lower than dark areas,even though the elevation difference was expected to be extremely small. A darkarea seen at the illuminated limb, or edge, of the planet seemed to be a notch or
depression. But this could be understood merely in terms of the darkness of thedark area: If it were dark against a dark sky, we would not see it at all. We might
gain the mistaken impression of a notch or depression. The prevailing opinion ofmost astronomers seems to have been that the dark areas were slightly lower thanthe bright, but the difference was estimated by Lowell as only half a mile or less.
In 1966, I re-examined this problem with Dr. James Pollack. We used two
main arguments. Mars has in its winter hemisphere a large polar cap which, atvarious times, has been ascribed to frozen water or frozen carbon dioxide. Even at
the present time its composition is unsettled; both substances are probably
present. As the polar cap retreats in each hemisphere, once each year, there areregions where frost is left behind. Later, when the frost leaves these regions, they
are found to be brighter than their surroundings. By analogy with the Earth, we
might expect them to be high mountainous regions that remain frosted after thesnows of the valleys have melted or evaporated. Indeed, one Martian polar region– the so-called Mountains of Mitchel – was identified as mountainous by thisargument alone.
But why are terrestrial mountains the last places to be frost-free? Because it iscolder as we walk uphill, as every mountaineer knows. But why does it get colder
as we walk uphill? Do the reasons that make terrestrial mountaintops colder thantheir bases apply to Mars?
We concluded that all factors that make it colder while walking uphill on the
Earth are inoperative on Mars, mainly because of the very thin Martian
atmosphere. But the winds on Mars should be higher at mountaintops than invalleys, as on Earth. This is not a conclusion from analogy, but is based on theappropriate physics. Therefore, we imagined that snows are removed by highwinds preferentially from the mountains of Mars, and that the bright areas thatretain frost on Mars are, therefore, low.
Our second line of attack was based on the radar observations of Mars, whichbegan in the middle 1960s. There was one piece of evidence that immediately
caught our attention. When the small central part of the radar beam waspositioned directly on a dark area of Mars, only a very small fraction of the radar
signal was returned to Earth. But when an adjacent bright area, on one side or theother of this dark region, was under the center of the radar beam, the reflectionwas much stronger. This could be understood if the dark area were either muchhigher or much lower than the adjacent bright area. From the preliminary radar
evidence then available, we concluded that if it had to be one or the other of these
two alternatives, the dark areas had to be systematically high on Mars. We
concluded that major elevation differences existed on Mars, in some cases as muchas ten miles between adjacent bright and dark areas. The large-scale slopes were at
most only a few degrees – not a very steep grade – and both the elevationdifferences and slopes were comparable to those on Earth, although the elevations
seemed to be greater than here. The notion that the deserts generally were
lowlands seemed consistent with the notion of fine sand and dust being trapped in
low valleys, with the tops of mountains – where the winds are higher – being
scoured of small, bright, fine particles.
In the few years following our analysis many more detailed radar studies weredone – principally by a group at the Haystack Observatory of the Massachusetts
Institute of Technology, headed by Professor Gordon Pettengill. For the first time
it was possible to do direct radar altitude measurements. Instead of using ourindirect arguments, the technology had reached a point where it was possible tomeasure how long it took the radar signal to reach Mars and be returned from it.
Those places on Mars from which the radar signal took longest to return were
farthest from us, and, therefore, deepest. Those regions from which the radar
signal took the least time to return were closer to us, and, therefore, highest. In
this way the first topographic maps of selected regions of the Martian surface wereconstructed. The maximum elevation differences and slopes were just about what
we had concluded by much more indirect means.
But dark areas did not appear to be systematically higher than bright areas.
Pettengill and his colleagues found that a bright region of Mars called Tharsis
appeared to be very high – perhaps the highest region sampled on the planet. A
major Martian bright circular area called Hellas – Greek for "Greece" – indeed
turned out to be very low from later nonradar observations. A somewhat similarfeature called Elysium, also large and bright and roughly circular, turned out to behigh. The darkest big Martian area, Syrtis Major, turned out to be a steep slope.
Why were Pollack and I only partly right? Because of Occam's Razor, aconvenient and frequently used principle in science, but one that is not infallible.
Occam's Razor recommends that, when faced with two equally good hypotheses,
we choose the simpler. We had assumed that dark areas were either systematicallyhigh or systematically low. If that were the case, dark areas would have to besystematically high. But that is not the case; dark areas can be either high or low.
Our conclusions only reflected our assumptions.

But I am very pleased that we were able, through logic and physics, to get thestory at least partly right, and to demonstrate that there are enormous elevationdifferences on Mars, elevations much vaster than Lowell had expected. I find it
more difficult, but also much more fun, to get the right answer by indirect
reasoning and before all the evidence is in. It's what a theoretician does in science.
But the conclusions drawn in this way are obviously more risky than those drawn
by direct measurement, and most scientists withhold judgment until there is more
direct evidence available. The principal function of such detective work – apartfrom entertaining the theoretician – is probably to so annoy and enrage theobservationalists that they are forced, in a fury of disbelief, to perform the criticalmeasurements.

Chapter 17: The Mountains of Mars
II. Observations From SpaceThe epic flight of Mariner 9 to Mars in 1971 produced a new set of definitive anddirect measurements concerning the mountains and elevations of Mars.
Moderately complete elevation terrain maps of Mars have been developed as aresult of the ultraviolet spectrometer, the infrared interferometric spectrometer,
and the S-band occultation experiments aboard Mariner 9. But the most striking
information on the mountains of Mars came from the television experiment.
The first pictures that Mariner 9 returned from Mars, obtained even before
orbital insertion on November 14, 1971, showed an almost completely featurelessplanet. The south polar cap could be discerned dimly, but the bright and darkmarkings, which had been seen and debated for over a century, were nowhere to
be found. This was not a failure of the television camera, but rather the result of aspectacular planet-wide dust storm, which had begun in late September andwould not significantly subside until early January.
The earliest pre-orbital pictures and the first few days of orbital pictures
showed no significant nonpolar detail – except in the region of Tharsis. Here, there
were four dark, somewhat irregular spots to be seen, three of them in an
approximate straight line running northeast to southwest; the fourth was isolatedaway from them and to the west. Since there was otherwise nothing much visibleon the planet, I devoted some attention to these spots in the early phases of themission – so much attention that for a while they were known as "Carl's Marks"
by several of my wittier co-investigators. I, in turn, proposed naming them Harpo,
Groucho, Chico, and Zeppo, but this was all before their significance wasestablished.
The isolated spot corresponded in position quite well with the classical Martianfeature named Nix Olympica – Greek for the Snows of Olympus, the home of thegods. The other three spots seemed to correspond to no familiar Martian surface
features. But Bradford Smith, astronomer at New Mexico State University,
pointed out that they corresponded quite well (as did Nix Olympica) to places on
Mars that exhibited local afternoon brightening as observed from Earth. In some ofSmith's ground-based telescopic photographs, obtained with a blue or violet filter
and when there was no dust storm on Mars, these four places appeared as brilliant
white spots, even though the contrast between the usual bright and dark areas wasvery small and the usual markings of Mars were indiscernible (the usual situation
when Mars is viewed in blue or violet light rather than in orange or red light).
Were we observing some sort of dark clouds in the midst of the dust storm at sites

where bright clouds were usually found?
Another Mariner 9 experimenter, William Hartmann of Science Applications,Inc., Tucson, Arizona, performed a computer contrast-enhancement of the original
photographs of the four spots and found some faint indication of circular central
regions in at least two of them. Indeed, the Mariner 6 and 7 photographs of Nix
Olympica, taken in 1969, showed a similar indication there.
By this time, the extent and severity of the dust storm had become evident,
and part of our preplanned mission for Mariner 9 to map the planet had to be
postponed. This then freed a significant picture-taking ability for high-resolution,
close-up photographs of the four spots. These experiments of opportunity werepossible only because Mariner 9 had a major adaptive capability. The scan
platform, on which the cameras were located, could be aimed at many desired
spots on Mars, and the technical staff of the Jet Propulsion Laboratory of the
California Institute of Technology was able to change its plans quickly enough toaccommodate the changed scientific needs of the mission. Because of the design ofthe spacecraft and the adaptability of its controllers, the first close-up photographsof the four spots began coming in.
Each spot had a vaguely circular center. There were parallel arcuate segments.
There was a kind of scalloping. All these features were dark against a brightsurrounding, corresponding to the dark appearance of the spots as seen initially in
low resolution.
The particular shapes that we had seen in the early pictures held no particularsignificance for me. But I was struck by the fact that these circular features
occurred in Tharsis, the highest region on Mars. These features were craters. Why
were we seeing them and virtually no other Martian features? Because they must
be the highest regions in Tharsis, a region already enormously elevated. The four
spots, therefore, seemed to me to be vast mountains poking through the dust. I
proposed that as time went on and the dust storm settled (from experience withother Martian global dust storms over decades of observation, we knew the dust
storms would have to settle eventually), we would see more and more of thesemountains, clear down to their bases. I even thought it possible that we could
produce topographic maps from the sequence of emerging detail as the dust
settled. Unfortunately, the settling out of the dust was a very irregular affair, andthis suggestion has not yet borne fruit.
Geologist members of the Mariner 9 television team, such as Harold Masursky
and John McCauley, of the U. S. Geological Survey, were taken with the form of

the craters, and quite early identified them – by analogy with similar features on
Earth – as vast volcanic piles with summit calderas. I have always been mistrustfulof arguments from terrestrial analogy. After all, Mars is quite another place. For all
we knew – at least, for all I knew – quite different geological processes might
operate there, and Earth-like features might be produced by different causes.
However, by another route I reached the same conclusion as the geologists:
There are only two processes we know that produce craters – the impact ofinterplanetary debris (the origin, for example, of most of the craters on the Moon)and vulcanism. It would be asking too much to expect that the large meteorites orsmall asteroids that carved out four of the largest impact craters in Tharsis knew
enough to land on the top of the four highest mountains in Tharsis. Much moreplausible is the idea that the mechanism that made the mountain made the crater.
That mechanism is called vulcanism.
As the dust storm cleared, the true magnitude of these four volcanic mountains
became clear. The largest of them, Nix Olympica, is five hundred miles across,larger than the largest such feature on the Earth, the Hawaiian Islands. The
altitudes of the spots have not yet been determined with precision, but they
appear to be ten to twenty miles above the mean level of the planet. (We cannot
talk of sea level on Mars because there are not – today, at any rate – any seas
there.) Over a dozen smaller volcanoes have since been found in other regions of
Mars.
The infrared radiometer on Mariner 9 showed no sign of hot lava in thesummit calderas of the craters. On the other hand, their fresh appearance and thealmost total absence of meteorite cratering on their slopes show them to be very
young objects, geologically speaking – probably no more than a few hundred
million years old, possibly younger.
The association of clouds with these volcanic mountains could be due tocontemporary outgassing from the calderas – steam, for example, being exhaled up
volcanic vents. But it seems more likely that the clouds are present at the summitsof these mountains precisely because these mountains are so high. An imaginary
parcel of Martian air, rising along the slope of the mountain, expands and cools.
(The air gets colder as we go upward in the Martian atmosphere. But because theair is so thin on Mars, it cannot exchange heat well with the surface; thus thesurface does not get cold as we go uphill on Mars, as we discussed earlier.) Whenthe temperature in the parcel of air drops below the freezing point of water, all of
the water vapor in the parcel condenses out into ice crystals. The amount of water
vapor we know to exist in the Martian atmosphere, the heights of the mountains,
and the amount of small ice crystals necessary to produce a visible cloud together

work out correctly for this to be the explanation of mountain clouds on Mars.
Recent vulcanism on Mars implies outgassing, whether or not the clouds that
we see at the summits of these volcanoes are signs of outgassing. When hot lava
flows to the surface, it carries with it a significant amount of gas – on the Earth,mainly water, but with a significant amount of other materials. Thus, thevolcanoes that we see on Mars must have made an important contribution to theMartian atmosphere. In part, at least, the air has come out of these holes in the
ground. Because Mars is so cold today, water can be trapped in many forms, suchas ice, and not remain in the atmosphere. Much more gas could have been
produced by these volcanoes than we see in the Martian atmosphere today. If
there is life on Mars, it will almost surely be based on the exchange of material
with the atmosphere – just as on Earth, where the cycle of green-plant
photosynthesis and animal respiration is predominant. If there is life on Mars,
these volcanoes may – at least indirectly – have played an important role in its
present development.
After the dust storm cleared, Mariner 9 was moved into a higher orbit, tofacilitate the geological mapping originally planned. The spacecraft worked manytimes longer than its designers had expected. Complete geological coverage of theplanet has been accomplished down to a resolution of half a mile. The resulting
geological maps reveal an enormous array of linear ridges and grooves thatsurround the Tharsis Plateau – as if a third or a quarter of the whole surface ofMars were cracked in some colossal recent event that lifted Tharsis. The mostspectacular of these quasilinear features is an enormous rift valley in a region called
Coprates. It runs 80 degrees of Martian longitude and is almost exactly as long as
the largest rift valley on the Earth, the East African Rift Valley, which runs up theentire east coast of Africa to the Dead Sea. Since Mars is a smaller planet, theCoprates Rift Valley is, relatively speaking, a much more impressive feature.
The East African Rift Valley occurs because of sea floor spreading andcontinental drift. The African and Asian continents are slowly moving away fromeach other, and the chasm that is developing there is the East African Rift Valley.
But continental drift is thought to be due to the slow circulation of material in the
mantle of the Earth. Should we then conclude that Mars, despite its smaller sizeand lower internal temperatures, also has mantle convection and continental drift?
Or is it possible that different processes produce similar features on the twoplanets?
Whatever the answer, we cannot help but learn a great deal more about theold Earth-bound science of geology – with its practical future disciplines, such as
earthquake prediction and control – by examining the geology of our neighboring
planet Mars.

Chapter 18: The Canals of Mars
In 1877 (as in 1971) the planet Mars was close – forty million miles from Earth.
European astronomers, with newly developed telescopes, prepared for what wasthen Man's most detailed look at our planetary neighbor. One of them was
Giovanni Schiaparelli, an Italian observing in Milan and a collateral relative of thepresent couturier and perfume enterpriser.
Generally speaking, the telescopic view of Mars was blurred and fuzzy,interrupted by the variable turbulence in the Earth's atmosphere that astronomers
call "seeing." But there were moments when the Earth's atmosphere steadied andthe true detail on the disc of Mars seemed to flash out. Schiaparelli was astonishedto see a network of fine straight lines covering the disc of Mars. He called theselines canali, which in Italian means "channels." However, canali was translated
into English as "canals," a word with a clear imputation of design.
Schiaparelli's observations were taken up by Percival Lowell, a diplomat once
posted in Chosen, the present Korea. A Boston Brahmin, the brother of thepresident of Harvard University and of an even more famous personage, thepoetess Amy Lowell (for some reason renowned for smoking little black cigars),
Lowell established a private observatory in Flagstaff, Arizona, to study the planet
Mars. He found the same canali that Schiaparelli had. He extended theirdescription and elaborated an explanation.
Mars was, Lowell concluded, a dying world on which intelligent life had arisen
and accommodated itself to the perils of the planet. The chief peril was the dearthof water. The Martian civilization, Lowell imagined, had constructed an extensive
network of canals to carry water from the melting polar caps to the habitations inmore equatorial climes. The turning point of the argument was the straightness ofthe canals, some of them following great circles for thousands of miles. Suchgeometrical configurations, Lowell thought, could not be produced by geologicalprocesses. The lines were too straight. They could only have been produced byintelligence.
This is a conclusion with which we all can agree. The only debate is about
which side of the telescope the intelligence was on. Lowell believed that the
penchant for Euclidian geometry was on the distant end of the telescope. But thedifficulties in drawing a great deal of mottled fine detail in a few seconds of goodseeing are so great that the eye-brain-hand combination is sorely tempted toconnect such disconnected features into straight lines. Many of the best visual
astronomers observing Mars between the turn of the century and the dawn of thespace age found that, while they could see canals under conditions of good but notsuperb seeing, they were able in the extremely rare moments of perfect seeing toresolve the straight lines into a multitude of spots and irregular detail.
Then it was found that at least the vast bulk of the polar caps are carbon
dioxide and not frozen water. The atmospheric pressure was discovered to bemuch less than on Earth. Liquid water was found to be entirely impossible. The
idea of advanced forms of life and canals on Mars died. And yet …
As the planet-wide dust storm cleared in 1971, the Mariner 9 spacecraft beganto photograph a region called Coprates by the classical observers. Coprates was
one of the largest canali found by Lowell, Schiaparelli, and their followers.
Toward the end of the dust storm, Coprates was revealed to be an enormous rift
valley running three thousand miles east to west near the Martian equator, fifty
miles wide in spots and a mile deep. It was not perfectly straight – it was certainly
not an engineering work; but it was a vast gash proportionately longer than any
such feature on Earth.
And running out of Coprates were features that were very curious indeed –sinuous channels, meandering through the highlands above the Coprates Valley
and graced with beautiful little tributaries. If such channels had been seen on
Earth, they would unhesitatingly have been attributed to running water. But on
Mars the surface pressures are so low that liquid water would instantly vaporize,
just as the pressures on Earth are so low that liquid carbon dioxide vaporizes
instantly. On Earth we have solid carbon dioxide and gaseous carbon dioxide, but
not liquid carbon dioxide. On Mars this absence of the liquid phase is true as well
for water.
But as the Mariner 9 photographic mission continued, a variety of additional
channels were discovered: Channels with second- and third-order tributarysystems, channels without a crater at their beginning or end, channels with
teardrop-shaped islands in their midst, channels with braided termini, like thosecut on Earth by episodic flooding.
There seems to be little doubt that most of the several dozen longest suchchannels (the longest are hundreds of miles long), and hundreds of smaller ones,
were cut by running water. But since there can be no liquid water on Mars today,
the channels must have been cut in a previous epoch of Martian history – when
the total pressures were larger, the temperatures higher, and the availability ofwater greater.

The channels revealed by Mariner 9 speak eloquently of the possibility ofmassive climatic change on Mars. In this view, Mars is today in the throes of an ice
age, but in the past – no one knows just how long ago – it possessed much moreclement and Earth-like conditions.
The reasons for such dramatic climatic changes are still being hotly debated.
Before the Mariner 9 launch, I proposed that such climatic changes leading toepisodes of liquid water might occur on Mars. They might be driven by theprecession of the equinoxes, a well-known motion akin to the slow, drifting
precession of a rapidly spinning top. The precessional periods on Mars are
something like fifty thousand years. If we are now in a precessional winter, withan extensive North polar ice cap, twenty-five thousand years ago may have been
the precessional winter with an extensive polar ice cap in the South.
But twelve thousand years ago may have been the epoch of precessional springand summer. The dense atmosphere of that time is now locked away in the polar
caps. Twelve thousand years ago may have been a time on Mars of balmy
temperatures, soft nights, and the trickle of liquid water down innumerable
streams and rivulets, rushing out to join mighty, gushing rivers. Some of theserivers would have flowed into the great Coprates Rift Valley.
If so, twelve thousand years ago was a good time on Mars for life similar to theterrestrial sort. If I were an organism on Mars, I might gear my activities to theprecessional summers and close up shop in the precessional winters – as manyorganisms do on Earth for our much shorter annual winters. I would make spores;
I would make vegetative forms; I would go into cryptobiotic repose; I would
hibernate until the long winter had subsided. If this is indeed what Martianorganisms do, we may be arriving at Mars twelve thousand years too early – or too
late!
But there is a way to test these ideas. One way the hypothetical Martianorganisms would know that the precessional spring has arrived is by thereappearance of liquid water. Therefore, as Linda Sagan has mentioned, the recipe
for detecting life on Mars is "Add water." And this is just what the U. S. Viking
biology experiments, scheduled to land on Mars in 1976 and search for microbes,
will do. An automatic arm will drop two samples of Martian soil into liquid water.
A third sample will be inserted into a chamber with no liquid water. If the firsttwo experiments give positive biological results, and the third experiment does
not, some support will be given to this idea that Martian organisms are waiting out
the long winter.

But it is entirely possible that the designs of these experiments have been too
Earth-chauvinist. There may be Martian organisms that enjoy the present
environment and are drowned in liquid water. The idea of Martian organisms as
sleeping beauties, awaiting a somewhat wet kiss from Viking, is a long shot – but afascinating one.
By no means do all of the channels correspond to the positions of the classicalcanali drawn by Lowell and Schiaparelli. Some, like Ceraunius, appear to be
ridges. Others correspond to no detail that can now be made out. But some, like
Coprates, are grooves in the Martian terrain. There are channels on Mars. They
may have biological implications, of a different sort than Lowell imagined (as thelong-winter model suggests), or they may have no connection with Martian
biology at all.
The canals of Lowell do not exist, but the canali of Schiaparelli are there to beseen, more or less. One day in the future, perhaps, the channels will again be filledwith water and, for all we know, with visiting gondoliers from the planet Earth.

Chapter 19: The Lost Pictures of MarsThe Mariner 9 mission to Mars radioed back to Earth 7,232 photographs thatrevolutionized our knowledge about the planet. Many hundreds of these pictures
were devoted to studying variable features, the time changes in the relative
configurations of bright and dark markings on the surface of the planet now
known to be due largely to wind-blown dust. We have found thousands of brightand dark streaks, beginning in local impact craters and stretching across tens ofmiles of Martian surface. They point in the direction of the prevailing winds. We
think they are produced by high winds carrying dust out of the craters anddepositing it on the surface beyond the crater ramparts. These streaks are natural
wind-direction indicators and, perhaps, anemometers laid down on the Martiansurface for our edification and delight. We have discovered dark irregular patchesor splotches, mostly residing in the interiors of craters, which tend to lie on theleeward walls of the craters. Thus, the splotches as well as the streaks are windindicators. Some of the splotches have been resolved by Mariner 9 into enormous
fields of parallel sand dunes.
We have discovered many cases of dark streaks and splotches varying throughthe mission in outline or extent. The positions and variabilities of these dark
features correspond well to the classical dark markings of Mars, observed byground-based astronomers for more than a century and most often attributed bythem to seasonally changing dark vegetation on the Martian surface. But ourMariner 9 evidence points unambiguously to a meteorological, rather than abiological, explanation of the Martian seasonal changes.
This in no way excludes life on Mars. It merely means that if there is life on
Mars, it is not easily detectable over interplanetary distances. The same is true inreverse: Photographic detection of life on Earth in daylight from the vantage pointof Mars is impossible, as we have found by studying several thousand orbital
photographs of our own planet. But the time-varying streaks and splotches on theMartian surface are a new and most exciting Martian phenomenon, which criesout for further study.
Since the Martian changes occur slowly, the variable-features objectives
required very long time intervals between two pictures of the same region to see
what changes had occurred. At the very end of the mission, fifteen photographs
were successfully taken by the Mariner 9 cameras of regions in Syrtis Major andTharsis, important for understanding the long-term variations. But when the timecame to point the high-gain antenna of Mariner 9 to the Earth, so that thesepictures could be transmitted by playing back the spacecraft's tape recorder, thelast of the attitude-control gas was used up, Earth-lock could not be acquired, andplayback did not occur. The spacecraft had literally run out of gas.
About a year before the Mariner 9 mission was launched, the possibility wasraised that the spacecraft would run out of control gas. A solution was proposed:
That the propulsion tanks be connected to the attitude-control gas system – a kindof spacecraft anastamosis. Excess propulsion gas could then be used for attitudecontrol in case the attitude-control nitrogen was exhausted. This possibility was
rejected – largely because of its expense. It would have cost $30,000. But no one
expected Mariner 9 to last long enough to use up its attitude-control gas. Its
nominal lifetime was ninety days – and it lasted almost a full year. The engineers
had been overly conservative in assessing their superb product.
In retrospect, it sounds very much like false economy. With an adequate
supply of attitude-control gas, the spacecraft might have lasted another full year inorbit around Mars. About $150 million of science might have been bought for$30,000 of pipe. Had we known that the spacecraft would die from a lack ofnitrogen, I am almost certain that the planetary scientists involved would haveraised the $30,000 themselves.
In fact, there are many such critical junctures in the space program where theaddition of only a small amount of money can greatly increase the scientific returnfrom a given mission. But NASA, severely limited by funding limitations imposedby Congress, the White House, and the Office of Management and Budget, has not
had such small increments of money. If it were possible, and if a generous donor
could be found, this would be a superb use for private philanthropy.
But these are idle musings. No anastamosis was performed; the final playback
was not accomplished. Sitting there still on the Mariner 9 tape recorder are fifteen
vital photographs of the planet. They will never be returned under Mariner 9's
own power. It has now also lost solar lock; sunlight is no longer being converted toelectricity on its four great solar panels, and there is no way to reactivate it. We
may never know what Tharsis and Syrtis Major looked like around the beginningof November 1972 from the vantage point of Martian orbit.
Or perhaps we will. Mariner 9 is in an orbit that is slowly decaying in theMartian atmosphere. But the decay is so slow that the spacecraft will not crashinto Mars for another half century. Long before then there should be manned
orbital flights around Mars. Rendezvous and docking maneuvers are reasonably
well developed in manned missions even now. Perhaps, then, sometime around1990, as a small side-trip in a grand manned-orbital exploration of Mars, there will

be a rendezvous with Mariner 9. The old and battered spacecraft will be taken
aboard a large manned station and returned home – perhaps to be put in theSmithsonian Institution; perhaps to prevent terrestrial micro-organisms on Mariner
9 from reaching Mars; but perhaps, also, to rescue and read off the fifteen lost
pictures of the Mariner 9 mission.

Chapter 20: The Ice Age and the Cauldron
On our tiny planet, spinning in an almost circular orbit at a nearly constantdistance from our star, the climate varies, sometimes radically, from place to place.
The Sahara is different from the Antarctic. The Sun's rays fall directly on the
Sahara and obliquely on the Antarctic, producing a sizable temperature difference.
Hot air rises near the equator, cold air sinks near the poles – producing
atmospheric circulation. The motion of the resulting air current is deflected by
Earth's rotation.
There is water in the atmosphere, but when it condenses, forming rain or
snow, heat is released into the atmosphere, which in turn changes the motion of
the air.
Ground covered by freshly fallen snow reflects more sunlight back to spacethan when it is snow-free. The ground becomes colder yet.
When more water vapor or carbon dioxide is put into the atmosphere, infraredemission from the surface of the Earth is increasingly blocked. Heat radiation
cannot escape from this atmospheric greenhouse, and the Earth's temperaturerises.
There is topography on Earth. When wind currents flow over mountains or
down into valleys, the circulation changes.
At one point in time on one tiny planet, the weather, as we all know, iscomplex. The climate, at least to some degree, is unpredictable. In the past there
were more violent climatic fluctuations. Whole species, genera, classes, andfamilies of plants and animals were extinguished, probably because of climaticfluctuations. One of the most likely explanations of the extinction of the dinosaurs
is that they were large animals with poor thermoregulatory systems; they wereunable to burrow, and, therefore, unable to accommodate to a global decline intemperature.
The early evolution of man is closely connected with the emergence of the
Earth from the vast Pleistocene glaciation. There is an as yet unexplained
connection between reversals of the Earth's magnetic field and the extinction oflarge numbers of small aquatic animals.
The reason for these climatic changes is still under serious debate. It may bethat the amount of light and heat put out by the Sun is variable on time scales oftens of thousands or more years. It may be that climatic change is caused by theslowly changing direction between the tilt of the Earth's rotational axis and its
orbit. There may be instabilities connected with the amount of pack ice in the
Arctic and Antarctic. It may be that volcanoes, pumping large amounts of dust
into the atmosphere, darken the sky and cool the Earth. It may be that chemical
reactions reduced the amount of carbon dioxide and other greenhouse moleculesin the atmosphere, and the Earth cooled.
There are, in fact, some fifty or sixty different and, for the most part, mutually
exclusive theories of the ice ages and other major climatic changes on Earth. It is aproblem of substantial intellectual interest. But it is more than that. An
understanding of climatic change may have profound practical consequences –because Man is influencing the environment of the Earth, often in ways poorly
thought-out, ill-understood, and for short-term economic profit and individual
convenience, rather than for the long-term benefit of the inhabitants of the planet.
Industrial pollution is churning enormous quantities of foreign particulatematter into the atmosphere, where they are carried around the globe. The smallest
particles, injected into the stratosphere, take years to fall out. These particles
increase the albedo or reflectivity of Earth and diminish the amount of sunlightthat falls on the surface. On the other hand, the burning of fossil fuels, such as coaland oil and gasoline, increases the amount of carbon dioxide in the Earth's
atmosphere which, because of its significant infrared absorption, can increase thetemperature of the Earth.
There is a range of effects pushing and pulling the climate in opposite
directions. No one fully understands these interactions. While it seems unlikelythat the amount of pollution currently deemed acceptable can produce a major
climatic change on Earth, we cannot be absolutely sure. It is a topic worth serious
and concerted international investigation.
Space exploration plays an interesting role in testing out theories of climaticchange. On Mars, for example, there are periodic massive injections of fine dust
particles into the atmosphere; they take weeks and sometimes months to fall out.
We know from the Mariner 9 experience that the temperature structure andclimate of Mars are severely changed during such dust storms. By studying Mars,
we may better understand the effects of industrial pollution on Earth.
Likewise for Venus. Here is a planet that appears to have undergone a runaway
greenhouse effect. A massive quantity of carbon dioxide and water vapor has been
put into its atmosphere, so cloaking the surface as to permit little infrared thermal
emission to escape into space. The greenhouse effect has heated the surface to 900

degrees F or more. How did this greenhouse-overkill happen on Venus? How do
we avoid its happening here?
Study of our neighboring planets not only helps us to generalize the study of
our own, but it has the most practical hints and cautionary tales for us to read – if
only we are wise enough to understand them.

Chapter 21: Beginnings and Ends of the Earth
Stars, like people, do not live forever. But the lifetime of a person is measured in
decades, the lifetime of a star in billions of years.
A star is born out of interstellar clouds of gas and dust. For a while, it stably
converts hydrogen to helium in the thermonuclear furnaces of its deep interior.
Then, in stellar old age, it encounters a set of minor or major catastrophes – a slow
trickle or an explosive injection of star-stuff into space. During the more or lessstable portion of the lifetime of the star, the hot interior region, convertinghydrogen into helium, gradually eats its way outward from the very center. In thecourse of time, the star becomes slowly, almost imperceptibly, brighter.
After the flares and other impetuosities of its early adolescence, our Sun settled
down to a more or less constant radiation output. But four billion years ago it was
about 30 percent dimmer than it is today. If we assume that four billion years ago
the Earth had the same distribution of land and water, clouds and polar ice, so thatit absorbed the same relative amount of sunlight as it does today, and if we also
assume that it had the same atmosphere as it does today, we can calculate what its
temperature would have been. The calculation reveals a temperature for the entire
Earth significantly below the freezing point of seawater. In fact, even two billion
years ago, under these assumptions, the Sun would not have been bright enough tokeep the Earth above the freezing point.
But we have a wide variety of evidence that this was not the case. There are inold mud deposits ripple marks caused by liquid water. There are pillow lavas
produced by undersea volcanoes. There are enormous sedimentary deposits thatcan only be produced on ocean margins. There are biological products, called algal
stromatolites, which can only be produced in water.
So what is wrong? Either our theory of the evolution of the Sun is wrong or
our assumption that the early Earth is like the present Earth is wrong. The theoryof solar evolution seems to be in good shape. What uncertainties exist do notappear to affect the question of the Sun's early luminosity.
The most likely resolution of this apparent paradox is that something wasdifferent on the early Earth. After studying a wide range of possibilities, I conclude
that what was different, two billion years ago and earlier, was the presence ofsmall quantities of ammonia in the Earth's atmosphere. Ammonia is present on
Jupiter today; it is the form of nitrogen expected under primitive conditions. It
absorbs very strongly at the infrared wavelengths that the Earth likes to emit tospace. Ammonia on the primitive Earth would have held heat in, increasing thesurface temperature through the greenhouse effect and keeping the global
temperature of Earth at congenial levels – for the origin and early history of lifeand for liquid water to have been abundant early in the history of the planet. And
ammonia is one of the atmospheric constituents needed for making the building
blocks of life. The study of the Sun's evolution leads us to information about theearly history, chemical composition, and temperature of the Earth, and, therefore,
to the circumstances of its habitability. Stellar and biological evolution areconnected.
What about the future evolution of the Sun? The Sun is steadily growing
brighter. About four billion years from now the Sun will be sufficiently brighterthat there will be a greatly enhanced runaway greenhouse effect on Earth, just as
there is today on Venus. Our oceans will boil, and carbon dioxide, now present ascarbonates in the sedimentary rocks, will pour out into the atmosphere. The Earthwill be an uninhabitable cauldron.
It is conceivable that the technology of those remote times will be equal to thetask of preventing such a runaway, but it will be an extremely difficult engineering
job. However, remarkably, the same increase in the brightness of the Sun somebillions of years from now will convert Mars from a place where the averagetemperature is 100 degrees F below zero to a place that has temperatures almost
exactly the same as those on Earth today.
When the Earth becomes uninhabitable, Mars will gain a balmy and clement
climate. Our remote descendants, if any, may wish to take advantage of thiscoincidence.

Chapter 22: Terraforming the Planets
Both subtly and profoundly, the activities of life have affected the environment ofour planet. Our atmosphere is composed of 20 percent oxygen and 80 percent
nitrogen. The oxygen is produced almost entirely by green-plant photosynthesis.
Similarly, the most recent evidence suggests that nitrogen is almost entirely aproduct of the biological activity of soil micro-organisms, which convert nitrates
and ammonia into the gas N2, molecular nitrogen. Not only are the principal
constituents of our atmosphere closely controlled by biological activities, but theminor constituents are as well. To a significant extent, carbon dioxide is also
buffered by the photosynthesis/respiration feedback loop. Even so minor aconstituent of the Earth's atmosphere as methane, CH4, is of biological origin.
In fact, life on Earth, invisible to photography, could be detectable with a small
telescope and an infrared spectrometer from the vantage point of Mars. The
Martians, if any, could easily observe, at a wavelength of 3.33 microns in theinfrared, a strong absorption feature that straightforward analysis would reveal tobe due to one part per million of methane in the terrestrial atmosphere. It should
not be difficult to deduce that the methane is probably of biological origin.
Methane is chemically unstable in an excess of oxygen. It is oxidized rapidly tocarbon dioxide:
CH4+2O2=CO2+2H2O.
The amount of methane that would be in equilibrium with the great excess ofoxygen in our atmosphere is less than one billion billion billionth the amountactually observed. How can this be? Methane must be produced at a rate so rapidthat there is not time enough for oxygen to reduce its abundance to theequilibrium amount. It might be that there are massive outpourings of methanefrom ancient petroleum fields on Earth. But because of the huge output required,this is a very unlikely hypothesis. It is far more likely that methane is produced bya biological process.
And this is indeed the case. There seems to be a debate in the ecologicalliterature on two possible sources of this methane. One source is methanebacteria, which live in swamps and marshes – hence the term "marsh gas" to refer
to methane. The principal other habitat of methane bacteria is in the rumens ofungulates. There is at least one school of ecological thought that believes that
more methane is produced from the latter source than from the former. Thismeans that bovine flatulence – the intimate intestinal activities of cows, reindeer,elephants, and elk – is detectable over interplanetary distances, while the bulk of
the activities of mankind are invisible. We would not ordinarily consider theflatulence of cattle as a dominant manifestation of life on Earth, but there it is.
Inadvertently, with no conscious effort by mankind, life on Earth has reworked
the environment in a major way. Through the effect of atmospheric pressure andcomposition on the climate, there is a feedback loop in which the climate itself
may to some degree be controlled by the gas exchange reactions in which the life
forms on Earth engage. In a way, life on Earth has terraformed Terra. It has tosome extent made the Earth the way it is.
Is it possible that at some time in the future we might be able similarly toterraform other planets, to convert a Mars or Venus, today inhospitable to Man,
into a clement and habitable environment? Such a change, if possible at all, should
be done only after the most careful and responsible examination of theconsequences. We would first want to understand thoroughly the present
environment of the planet before altering it. We must scrupulously guarantee that
any indigenous organisms on the planet would not be disrupted by terraforming. If
Mars, for example, has a population of indigenous organisms that would be
extinguished by terraforming, we should never perform such terraforming. But if
the planet is lifeless, or if the organisms survive better under conditions closer toour own, it might be reasonable at some time in the future to consider such analteration of a planetary environment.
Our motivations for planetary re-engineering must be clear. This is not asolution to the overpopulation problem. Several hundred thousand people areborn every day on Earth. There is certainly no prospect in the immediate future oftransshipping hundreds of thousands of people to other planets each day. In its
entire history mankind has managed to launch one dozen people to anothercelestial body. Nor are we likely to see in the immediate future a thriving mining
industry in which ores are extracted from another planet and transshipped to
Earth: The freightage would be prohibitive.
And yet the human spirit is expansive; the urge to colonize new environments
lies deep within many of us. Such activities can be performed without cosmic
imperialism, without the kind of arrogance that characterized the European
colonization of the New World, or the encroachment on the Indians in the settlingby whites of the American West. Interplanetary colonization can be consistent
with the highest aspirations and goals of mankind.
How would we do it? In the case of Venus, as we saw in Chapter 12, there is acrushing atmosphere, composed largely of carbon dioxide, and a searing surface
temperature in excess of 900 degrees F. It would seem to be a formidable task
indeed to convert this environment into one in which men could live and workwithout enormous technological assistance. But there is a bare possibility of reengineering Venus into a quite Earth-like place, a possibility I suggested with somecaution in 1961. The method assumes that the high surface temperature is
produced by a greenhouse effect involving carbon dioxide and water, a conjecturethat is much more plausible now than it was then. The idea is simply to seed theclouds of Venus with a hardy variety of algae – a genus called Nostocacae wassuggested – which would perform photosynthesis in the vicinity of the clouds.
Carbon dioxide and water would be converted into organic compounds, largely
carbohydrates, and oxygen. The algae would, however, be carried by theatmospheric circulation down to deeper and hotter levels in the Venus
atmosphere, where they would be fried. Frying an alga releases simple carbon
compounds, carbon, and water into the atmosphere. The water content of theatmosphere thus remains fixed, and the net result is the conversion of carbon
dioxide into carbon and oxygen.
The present greenhouse effect on Venus is due largely to carbon dioxide andwater. The present total pressure on Venus is about ninety times that on thesurface of Earth. The Venus atmosphere is largely composed of carbon dioxide. As
the carbon dioxide is converted into carbon and oxygen, and the oxygen ischemically combined with the crust of Venus, the total pressure would decline,
decreasing atmospheric infrared absorption, reducing the greenhouse effect, andlowering the temperature.
It is possible, therefore, that the injection of appropriately grown algae into theclouds of Venus, algae able to reproduce there faster than they are fried, would intime convert the present extremely hostile environment of Venus into one much
more pleasant for human beings.
The amount of water vapor in the Venus atmosphere, if condensed on thesurface of the planet, would give a layer of water about one foot high – not an
ocean, but enough to do irrigation and to provide for other human needs. It is also
possible that water is available bound to the rocks on the surface of the planet.
No one can estimate whether this is a very likely scenario, or how long it
would take to re-engineer the second planet from the Sun. It is perfectly possiblethat there is some flaw in the idea. For example, the high surface temperature may
not be due to a greenhouse effect, but I think this is unlikely.
In any case, I think terraforming Venus is not impossible. The Nostoc scheme
is an example of how human technology and science may, in periods quite shortcompared to geological time, rework the environment of another planet.
For Mars, as we saw in Chapter 18, there is now evidence that in comparatively

recent times conditions on that planet were much more Earth-like than they aretoday. We mentioned the likelihood that enormous quantities of carbon dioxide
and water are locked in the Martian polar caps, trapped as permafrost andchemically bound to the surface material elsewhere on the planet. Much of thisCO2 and H2O may be released from the polar caps into the atmosphere twice eachprecessional cycle of fifty thousand years. Drs. Joseph Burns and Martin Harwit ofCornell University have considered a variety of technological schemes to induce
more clement conditions on Mars hundreds of years from now, rather thanthousands. These schemes involve alteration of the orbits of the Martian satellites
or of a nearby asteroid to change the precessional motion of the planet, or the
installation of an enormous orbiting mirror over the polar cap to melt the material
frozen there. Even easier, however, might be to sprinkle carbon black over thecaps, heat up the poles, increase the atmospheric pressure, and warm the planet.
Again, we do not know that such schemes will work, but they do not seemextremely impractical. It may very well be that on time scales of hundreds of years
we will have the capability of converting Mars into a much more Earth-like planet
than it would otherwise be.
The Moon and the asteroids are much less hospitable than Mars and Venus.
They are so much less able to retain an atmosphere that the terraforming schemes
we have been discussing are inapplicable to them. But even on airless worlds, theestablishment of human colonies on their surfaces or even – in the case of small
asteroids – in their interiors seems a possible future project for mankind. Suchcolonies would be much more constrained than those on a re-engineered Mars or
Venus, and would require much greater attention to the husbanding of scarce
resources.
Such colonies would be tenable only if significant natural resources –particularly frozen or chemically bound water – were to be found. In the case of
the very surface of the Moon, the samples returned by Apollo astronauts showedvirtually no such water at all. But it is entirely possible that large stores of water
exist in cold, shadowed regions near the lunar poles or at substantial depths
beneath the lunar surface.
It is not unlikely that on a time scale of a few centuries there will be extensive
human colonies throughout the inner part of the Solar System and on some of the
major satellites of the Jovian planets. The prospect is, of course, a difficult one; theengineering tasks are immense and the need to retain ecological respect for otherenvironments pervasive. The danger of both forward and backward biologicalcontamination must always be examined scrupulously.

There may even come a day when we shall be called to account for our
stewardship of the Solar System. From that vantage point our own epoch will beviewed as a moment when we first left the cradle of our species and began, in a
groping and tentative way, to explore and transform the space surrounding us.

Chapter 23: The Exploration and Utilization of the Solar System
At the very beginning of the twentieth century competent scientific and lay
opinion held that airplanes were impossible. The end of the century, barring thedark specter of nuclear or ecological catastrophes, will probably see joint Soviet
and American manned space expeditions to the nearer planets.
This is the century in which some of the oldest dreams of Man have beenrealized, in which mankind has sprouted wings and realized the aspirations of
Daedalus and da Vinci. Air-breathing, man-carrying machines now circumnavigate
our planet in less than a day; other machines, skimming above the atmosphere,
carry men around our globe in ninety minutes.
There is a generation of men and women for whom, in their youth, the planets
were unimaginably distant points of light, and the Moon was the paradigm of theunattainable. Those same men and women, in middle life, have seen their fellows
walk upon the surface of the Moon; in their old age, they will likely see men
wandering along the dusty surface of Mars, their journeys illuminated by thebattered face of Phobos. There is only one generation of humans in the tenmillion-year history of mankind that will live through such a transition. That
generation is alive today.
This is also the moment in our history when, for the first time, the whole ofour planet has been explored, when tribalism is dissipating, when greattransnational groupings of states are being organized, when stunning technologicaladvances in communications and transportation are eroding the culturaldifferences among the various segments of mankind.
But cultural diversity is the forge for the survival of our civilization, just as
biological diversity is the forge for the survival of life.
The Earth is overcrowded. Not yet in a literal sense: Our technology isadequate to maintain comfortably a population significantly larger than ourpresent 3.6 billion. The Earth is overcrowded in a psychological sense. For that
restless and ambition-driven fraction of mankind that has blazed new paths for our
species, there are no new places to go. There are places inside of ourselves, but thisis not the forte of such individuals. There are the ocean basins, but we are not yet
committed to exploring them seriously; and when we do, they are likely to be
exploited rapidly.
At just this time in our history comes the possibility of exploring andcolonizing our neighboring worlds in space. The opportunity has come to us not a
moment too soon.
October 12, 1992, will be the five hundredth anniversary of the discovery of the"New World" by Christopher Columbus. Mankind will be, I think, engaged at thatvery moment in an enterprise similar to Columbus'. We will have advantages over
him and the mariners of his time. We know precisely where we are going and how
to get there. The way will have been examined by unmanned vessels going before
us. The paths will have been charted exactly. There will be hazards – collisions
with asteroids on voyages to the outer Solar System, for example, or mechanicalfailure. But there will be no fear of slipping off the edge of the world, as many of
the sailors of Columbus' time truly feared. And very likely there will not be a
Solar System equivalent of doldrums or sea monsters. Yet the same thrill of
exploration and the same adventuresome spirit that drove Columbus will be
driving us. As the discovery and exploration of the New World had a profoundand irreversible effect on European civilization, exploration and colonization of
the Solar System will produce permanent changes in the history and developmentof mankind.
The analogy with the epic sea voyages of centuries ago is, it seems to me,remarkably close. There was the initial set of sea voyages by Columbus, an Italianin the Spanish court. Our initial set of manned Apollo explorations of the Moon
was motivated in significant part by a group of expatriate German engineers led
by Wernher von Braun. After Columbus' four voyages, there was essentially ahiatus of a decade or so – and then a burst of further exploratory activities by the
Spanish, English, French, and Dutch – vessels flying many flags, many expeditionsorganized by foreign nationals.
Apollo 17 marked the end of the Apollo lunar missions. It seems clear, at leastin the United States, that there will be a hiatus of a decade or more before further
lunar exploration and lunar bases are organized. Apollo's primary orientation wasnever scientific. It was conceived at a time of political embarrassment for theUnited States. Several historians have suggested that a principal motivation of
President Kennedy in organizing the Apollo program was to deflect publicattention from the stinging defeat suffered at the Bay of Pigs invasion. Several tensof billions of dollars have been expended on the Apollo program. If the objective
had been scientific exploration of the Moon, it could have been carried out much
more effectively, for much less money, by unmanned vehicles. The early Apollo
missions went to lunar sites of little scientific interest, because the safety of theastronauts was the prime, almost the only, concern. Only toward the very end of
the Apollo series did scientific considerations play a significant role.

The Apollo program ended just as the first scientist landed on the Moon.
Harrison "Jack" Schmitt, a geologist, trained at Harvard, was one of the two-man
crew of the Apollo 17 landing module. He was the first scientist to study the Moon
from the surface of the Moon. It is ironic that just as the Apollo program became
able to achieve this major advance in the scientific exploration of the Moon, it wascanceled. Fittingly enough, the first scientist to land on the Moon was the last man
to land on the Moon – at least in the foreseeable future. There are no plans forfollow-on manned missions to the Moon either by the United States or, so far as
we know, by the Soviet Union.
The argument for cancellation of Apollo was economic. Yet the incremental
cost of a given mission was in the many tens of millions of dollars, something like
one thousandth the total cost of the Apollo program. It is very much as if, against
the advice of my wife, I purchase a Rolls-Royce automobile. She argues that a
Volkswagen could get me round just as well, but I feel that a Rolls-Royce would
take my mind off the troubles of my job. I then spend so much money on theRolls-Royce that, after driving it a little bit, I find I can drive it no more because I
cannot afford the price of a tank of gas – which is about one thousandth the costof a Rolls-Royce.
I was one of the scientists opposed to an early Apollo mission. But once theApollo technology was in hand, I was very much for its continuing usage. I believe
the wrong decision was made twice – once in opting for early manned missions to
the Moon, and later in abandoning such missions. After Apollo 17, the UnitedStates is left with no program, manned or unmanned, for exploration of the Moon.
The Soviet Union has developed, in its Luna series of unmanned spacecraft, aproven and versatile capability for roving exploration of the lunar surface andautomatic sample return to Earth.
The example of the earliest exploration of the New World suggests that the
hiatus in space will be only temporary. The linkage of Soyuz and Skylab, theorbital stations of the Soviet Union and the United States, scheduled for 1975 or
1976, is presaged as the predecessor for joint manned planetary missions.
The Solar System is much vaster than the Earth, but the speeds of ourspacecraft are, of course, much greater than the speeds of the sailing ships of the
fifteenth and sixteenth centuries. The spacecraft trip from the Earth to the Moonis faster than was the galleon trip from Spain to the Canary Islands. The voyage
from Earth to Mars will take as long as did the sailing time from England to North
America; the journey from Earth to the moons of Jupiter will require about thesame time as did the voyage from France to Siam in the eighteenth century.
Moreover, the fraction of the gross national product of the United States or theSoviet Union that is being expended even in the more costly manned space
programs is just comparable to the fraction of the gross national product spent byEngland and France in the sixteenth and seventeenth centuries on their
exploratory ventures by sailing ships. In economic terms and in human terms, wehave performed such voyages before!
I believe we will see semipermanent bases on the Moon by the 1980s. They
will initially be resupplied with material and personnel from Earth, but will
become increasingly self-sustaining, utilizing lunar resources. There will bechildren born in such colonies. They will eventually think of the Earth as "the oldcountry" – an old-fashioned world in many senses, set in its ways, not moving withthe times, more constrained and less free than the lunar colonies, despite the rigors
and technological constraints of life on the Moon.
In the comparatively near future the entire Solar System will be explored bysophisticated unmanned space vehicles. I think we will see by the 1980s and 1990s
deep-entry probes into the atmospheres of Jupiter and Saturn and Titan (thebiggest moon of Saturn) – places that are, I believe, far and away the mostfavorable in the Solar System for indigenous life; we will witness passages of small
spacecraft through comets, landings on the large satellites of Jupiter and Saturn,flybys as far as Neptune and Pluto, and hardy spacecraft that plunge into the Sun,
radioing back data before they sear and melt in the interior inferno of the neareststar.
Human landings on even the nearer planets, however, will not be as easy as had
once been thought. The surface of Venus, far from being Eden, turns out, as wehave seen, to be far more like Hell. We cannot imagine manned exploration of theVenus surface in the next few decades. Venus is a planet with fiery temperatures,
noxious gases, and crushing atmospheric pressures. Yet, the clouds of Venus are ina clement environment; and a manned buoyant probe – something like anineteenth-century balloon gondola in which the astronauts work in shirtsleevesand leather oxygen masks – is not without its charm or its scientific interest.
Mars is a vastly exciting planet, of enormous geological, meteorological, andbiological interest. A manned expedition to Mars would be very desirable, except
for two objections. First, the cost would be crushing. One hundred billion to two
hundred billion dollars is probably a conservative estimate. I cannot bring myself
to believe that such an expenditure is necessary in the next few decades – when
there is so much misery on Earth that could be relieved by such expenditures. Yetin the longer term, say, in the first decades of the twenty-first century, I do notthink that such cost objections will be cogent – particularly because new
propulsion and life-support systems will be developed.
The second objection to manned missions to Mars is more subtle. It is equally
an objection to automatically returned samples from Mars, like the Soviet Union's
Luna series for automatic sample return from the Moon. This is the danger of"back contamination." Precisely because Mars is an environment of great potential
biological interest, it is possible that on Mars there are pathogens, organisms
which, if transported to the terrestrial environment, might do enormous biologicaldamage – a Martian plague, the twist in the plot of H. G. Wells' War of theWorlds, but in reverse. This is an extremely grave point. On the one hand, we canargue that Martian organisms cannot cause any serious problems to terrestrialorganisms, because there has been no biological contact for 4.5 billion years
between Martian and terrestrial organisms. On the other hand, we can argue
equally well that terrestrial organisms have evolved no defenses against potential
Martian pathogens, precisely because there has been no such contact for 4.5 billion
years. The chance of such an infection may be very small, but the hazards, if it
occurs, are certainly very high. Wholesale exterminations of native populations in
Santo Domingo and Samoa and Tahiti occurred during the early days of sailingship exploration for just such reasons. Among the gifts carried by Columbus to the
New World was smallpox.
It is no use arguing that samples can be brought back safely to Earth, or to abase on the Moon, and thereby not be exposed to Earth. The lunar base will be
shuttling passengers back and forth to Earth; so will a large Earth orbital station.
The one clear lesson that emerged from our experience in attempting to isolate
Apollo-returned lunar samples is that mission controllers are unwilling to risk thecertain discomfort of an astronaut – never mind his death – against the remotepossibility of a global pandemic. When Apollo 11, the first successful manned lunarlander, returned to Earth – it was a spaceworthy, but not a very seaworthy, vessel– the agreed-upon quarantine protocol was immediately breached. It was adjudged
better to open the Apollo 11 hatch to the air of the Pacific Ocean and, for all wethen knew, expose the Earth to lunar pathogens, than to risk three seasick
astronauts. So little concern was paid to quarantine that the aircraft-carrier cranescheduled to lift the command module unopened out of the Pacific was
discovered at the last moment to be unsafe. Exit from Apollo 11 was required in the
open sea.
There is also the vexing question of the latency period. If we expose terrestrialorganisms to Martian pathogens, how long must we wait before we can beconvinced that the pathogen-host relationship is understood? For example, thelatency period for leprosy is more than a decade. Because of the danger of backcontamination of Earth, I firmly believe that manned landings on Mars should bepostponed until the beginning of the next century, after a vigorous program ofunmanned Martian exobiology and terrestrial epidemiology.
I reach this conclusion reluctantly. I, myself, would love to be involved in thefirst manned expedition to Mars. But an exhaustive program of unmanned
biological exploration of Mars is necessary first. The likelihood that such
pathogens exist is probably small, but we cannot take even a small risk with abillion lives. Nevertheless, I believe that people will be treading the Martiansurface near the beginning of the twenty-first century.
Beyond that, it is just possible to glimpse the outline of further exploration andcolonization. The large moons of Jupiter, and Titan, the biggest moon of Saturn,are major worlds in their own right. Titan is known to have an atmosphere muchthicker than that of Mars. These five moons all have large quantities of ices on
their surfaces. To make these worlds more habitable, their ices can be tapped for
fuel, for the production of food and for the generation of atmospheres. Schemes
for similarly terraforming Mars and Venus have been suggested and will very likely
be refined and implemented (see Chapter 22). More exotic possibilities, requiringmuch more advanced technologies, are not at all beyond the likely capabilities ofmankind in the next century or two. These include the establishment of bases on
and in the asteroids and the short-period comets.
In another century or so, novel forms of propulsion within the Solar System
will be developed. One of the most charming of these is solar sailing, the use of
the pressure of sunlight and of the protons and electrons in the solar wind fortripping through the Solar System. Enormous sails will be required for such anenterprise, but they can be extremely thin. We can imagine a spacecraftsurrounded with tens of miles of golden gossamer-thin sails, delicately andexquisitely furled to catch the solar wind. Remote scientific stations will be on the 131
lookout for the gusts produced by solar flares. Going outward from the Sun will
be easy; tacking inward will be more difficult. Spacecraft using solar electric power
and nuclear fusion will very likely also be developed in the next century.
In something like two or three centuries, assuming even a modest growth inour technological capability, I would imagine the entire Solar System will havebeen explored thoroughly – at least to the extent that the Earth has been exploredat the present time, some two or three centuries after the first large-scale
exploration and colonization activities were begun by European sailing vessels.
After that, it is not out of the question that a more wholesale rearrangement ofour Solar System will begin, first slowly and then at a more rapid rate –astroengineering projects to move the planets about, to rearrange their masses forthe convenience of mankind, his descendants, and his inventions.
By then – perhaps long before then – we may have made contact with otheradvanced civilizations in the Galaxy. Or perhaps not. In any case, we will be readyin a few centuries for the next step. At just the point the Solar System begins to
be filled in – again psychologically, rather than physically – we will be ready forinterstellar voyages. That is a limitless prospect, one that can occupy the best
exploratory instincts of mankind forever.
Pioneer 10 is the first interstellar spacecraft launched by mankind. It was also
the fastest spacecraft launched, to the date of its departure. But it will take eighty
thousand years for Pioneer 10 to reach the distance of the nearest star. Because
space is so empty, it will never enter another Solar System. The little golden
message aboard Pioneer 10 will be read, but only if there are interstellar voyagers
able to detect and intercept Pioneer 10.
I believe that such an interception may occur, but by interstellar voyagers fromthe planet Earth, overtaking and heaving to this ancient space derelict – as if theNina, with its crew jabbering in Castilian about falling off the edge of the world,
were to be intercepted, somewhere off Tristan da Cunha, by the aircraft carrierJohn F. Kennedy.

Part Three: BEYOND THE SOLAR SYSTEM
To dance beneath the diamond sky
With one hand wavin' free …
– Bob Dylan, Mr. Tambourine Man

Chapter 24: Some of My Best Friends Are Dolphins
The first scientific conference on the subject of communication withextraterrestrial intelligence was a small affair sponsored by the U. S. National
Academy of Sciences in Green Bank, West Virginia. It was held in 1961, a year
after Project Ozma, the first (unsuccessful) attempt to listen to possible radio
signals from civilizations on planets of other stars. Subsequently, there were twosuch meetings held in the Soviet Union sponsored by the Soviet Academy of
Sciences. Then, in September 1971, a joint Soviet-American conference on
Communication with Extraterrestrial Intelligence was held near Byurakan, in
Soviet Armenia (see Chapter 27). The possibility of communication withextraterrestrial intelligence is now at least semirespectable, but in 1961 it took agreat deal of courage to organize such a meeting. Considerable credit should go to
Dr. Otto Struve, then director of the National Radio Astronomy Observatory,
who organized and hosted the Green Bank meeting.
Among the invitees to the meeting was Dr. John Lilly, then of theCommunication Research Institute, in Coral Gables, Florida. Lilly was there
because of his work on dolphin intelligence and, in particular, his efforts tocommunicate with dolphins. There was a feeling that this effort to communicate
with dolphins – the dolphin is probably another intelligent species on our own
planet – was in some sense comparable to the task that will face us incommunicating with an intelligent species on another planet, should interstellar
radio communication be established. I think it will be much easier to understandinterstellar messages, if we ever pick them up, than dolphin messages (see Chapter
29), if there are any.
The conjectured connection between dolphins and space was dramatized forme much later, at the lagoon outside the Vertical Assembly Building at Cape
Kennedy, as I awaited the Apollo 17 liftoff. A dolphin quietly swam about,breaking water now and again, surveying the illuminated Saturn booster poised forits journey into space. Just checking us all out, perhaps?
Many of the participants at the Green Bank meeting already knew one another.
But Lilly was, for many of us, a new quantity. His dolphins were fascinating, andthe prospect of possible communication with them was enchanting. (The meeting
was made further memorable by the announcement in Stockholm during its
progress that one of our participants, Melvin Calvin, had been awarded the Nobel
Prize in Chemistry. )For many reasons, we wished to commemorate the meeting and maintain someloose coherence as a group. Captured as we were by Lilly's tales of the dolphins,
we christened ourselves "The Order of the Dolphins." Calvin had a tie pin struck
as an emblem of membership; it was a reproduction from the Boston Museum of
an old Greek coin showing a boy on a dolphin. I served as a kind of informal
coordinator of correspondence the few times that there was any "Dolphin"business, all of it the election of new members. In the following year or two, weelected a few others to membership – among them I. S. Shklovskii, Freeman
Dyson, and J. B. S. Haldane. Haldane wrote me that membership in an
organization that had no dues, no meetings, and no responsibilities was the sort oforganization he appreciated; he promised to try hard to live up to the duties ofmembership.
The Order of the Dolphins is now moribund. It has been replaced by a numberof activities on an international scale. But for me the Order of the Dolphins had a
special significance – it provided an opportunity to meet with, talk with, and, tosome extent, befriend dolphins.
It was my practice to spend a week or two each winter in the Caribbean,
mostly snorkeling and scuba diving – examining the non-mammalian inhabitantsof the Caribbean waters. Because of my acquaintance and later friendship withJohn Lilly, I was also able to spend some days with Lilly's dolphins in Coral Gables
and in his research station at St. Thomas in the U. S. Virgin Islands.
His institute, now defunct, unquestionably did some good work on thedolphin, including the production of an important atlas of the dolphin brain.
While I will be critical here about some of the scientific aspects of Lilly's work, I
want to express my admiration for any serious attempt to investigate dolphins andfor Lilly's pioneering efforts in particular. Lilly has since moved on toinvestigations of the human mind from the inside – consciousness expansion, both
pharmacologically and non-pharmacologically induced.
I first met Elvar in the winter of 1963. Laboratory research on dolphins had
been limited by these mammals' sensitive skin; it was only the development ofplastic polymer tanks that permitted long-term residence of dolphins in thelaboratory. I was surprised to find that the Communication Research Instituteresided in what used to be a bank, and I had visions of a polystyrene tank in eachteller's cage, with dolphins counting the money. Before introducing me to Elvar,
Lilly insisted that I don a plastic raincoat, despite my assurances that this was
entirely unnecessary. We entered a medium-sized room at the far corner of which
was a large polyethylene tank. I could immediately see Elvar with his head thrownback out of the water so that the visual fields of each eye overlapped, giving him

binocular vision. He swam slowly to the near side of the tank. John, the perfect
host, said, "Carl, this is Elvar; Elvar, this is Carl." Elvar promptly slapped his head
forward, down onto the water, producing a needle-beam spray of water that hitme directly on the forehead. I had needed a raincoat after all. John said, "Well, I
see you two are getting to know each other" – and promptly left.
I was ignorant of the amenities in dolphin/human social interactions. I
approached the tank as casually as I could manage and murmured something like
"Hi, Elvar." Elvar promptly turned on his back, exposing his abraded, gun-metalgray belly. It was so much like a dog wanting to be scratched that, rather gingerly, I
massaged his underside. He liked it – or at least I thought he liked it. Bottle-nose
dolphins have a sort of permanent smile set into their heads.
After a little while, Elvar swam to the opposite side of the tank and thenreturned, again presenting himself supine – but this time about six inches
subsurface. He obviously wanted his belly scratched some more. This was slightly
awkward for me because I was outfitted under my raincoat with a full armory ofshirt, tie, and jacket. Not wishing to be impolite, I took off my raincoat, removed
my jacket, slid my sleeves up onto my wrists without unbuttoning my shirt cuffs,
and put my raincoat on again, all the while assuring Elvar I would return
momentarily – which I did, finally scratching him six inches below the water.
Again he seemed to like it; again, after a few moments, he retreated to the far sideof the tank, and then returned. This time he was about a foot subsurface.
My mood of cordiality was eroding rapidly, but it seemed to me that Elvar andI were at least engaged in communication of a kind. So I once again removed myraincoat, rolled up my sleeves, put my raincoat on again, and attended to Elvar.
The next sequence found Elvar three or four feet subsurface, awaiting my massage.
I could just have reached him were I prepared to discard raincoat and shirt
altogether. This, I decided, was going too far. So we gazed at each other for a while
in something of a standoff – man and dolphin, with a meter of water between us.
Suddenly, Elvar came booming out of the water head first, until only his tail flukes
were in contact with the water. He towered over me, doing a kind of slow backpedaling, then uttered a noise. It was a single "syllable," high-pitched and squeaky.
It had, well, a sort of Donald Duck timbre. It sounded to me that Elvar had said
"More!"
I bounded out of the room, found John attending to some electronicequipment, and announced excitedly that Elvar had apparently just said "More!"

John was laconic. "Was it in context?" was all he asked.
"Yes, it was in context.""Good, that's one of the words he knows."
Eventually, John believed that Elvar had learned some dozens of words ofEnglish. To the best of my knowledge, no human has ever learned a single word ofdelphinese. Perhaps this calibrates the relative intelligence of the two species.
Since the time of Pliny, human history has been full of tales of a strange
kindred relation between humans and dolphins. There are innumerable
authenticated accounts of dolphins saving human beings who would otherwise
have drowned, and of dolphins protecting human beings from attack by other sea
predators. As recently as September 1972, according to an account in the New
York Times, two dolphins protected a twenty-three-year-old shipwrecked womanfrom predatory sharks during a twenty-five-mile swim in the Indian Ocean.
Dolphins are pervasive and dominant motifs in the art of some of the most ancient
Mediterranean civilizations, including the Nabatean and Minoan. The Greek cointhat Melvin Calvin had duplicated for us is an expression of this long-standing
relation.
What humans like about dolphins is clear. They are friendly, and faithful; attimes they provide us with food (some dolphins have herded sea animals tofishermen); and they occasionally save our lives. Why dolphins should be attracted
to human beings, what we do for them, is far less clear. I will propose later in thischapter that what we provide for dolphins is intellectual stimulation and audio
entertainment.
John was replete with dolphin anecdotes of first- or secondhand. I remember
three stories in particular. In one, a dolphin was captured in the open sea, putaboard a small ship in a plastic tank, and confronted his captors with a set ofsounds, whistles, screeches, and drones that had a remarkably imitative character.
They sounded like seagulls, fog horns, train whistles – the noises of shore. The
dolphin had been captured by shore creatures and was attempting to make shore
talk, as a well-brought-up guest would.
Dolphins produce most of their sounds with their blow hole, which produces
the spout of water in their cousins the whales, of whom they are close, miniature
anatomical copies.
In another tale, a dolphin held in captivity for some time was let loose in the
open sea and followed. When it made contact with a school of dolphins, there wasan extremely long and involved sequence of sounds from the liberated prisoner.
Was it an account of his imprisonment?
Besides their echo-location clicks – a very effective underwater sonar system –dolphins have a kind of whistle, a kind of squeaky-door noise, and the noise madewhen imitating human speech, as in Elvar's "More!" They are capable of producing
quite pure tones, and pairs of dolphins have been known to produce tones of thesame frequency and different phase, so that the "beat" phenomenon of wave
physics occurs. The beat phenomenon is a lot of fun. If humans could sing puretones, I am sure we would go on beating for hours.
There is little doubt that the whistle noises are used for dolphin
communications. I heard what seemed to be (I may be anthropomorphizing) very
plaintive whistles on St. Thomas from a male adolescent dolphin named Peter,
who, for a while, was kept in isolation from two adolescent female dolphins. They
all whistled a lot at each other. When the three were reunited in the same pool,
their sexual activity was prodigious, and they did not whistle much.
Most of the communication among dolphins that I have heard is of thesqueaky-door variety. Dolphins seem to be attracted to humans who make similar
noises. In March 1971, for example, in a dolphin pool in Hawaii, I spent forty-fiveminutes of vigorous squeaky-door "conversation" with several dolphins, to at least
some of whom I seemed to be saying something of interest. In delphinese it may
have been stupefying in its idiocy, but it held their attention.
In another story, John told how it was his practice with dolphins of adolescentage and sexual proclivities to separate male and female over the weekend when
there would be no experiments. Otherwise, they would do what John, with somedelicacy, described as "going on a honeymoon" – which, however desirable to thedolphins, would leave them in no condition for experimentation on Monday
morning. In one case, dolphins could pass across a large tank, from one half to theother, only through a heavy, vertically sliding door. One Monday morning John
found the door in place but the two dolphins of opposite sex, Elvar and Chi-Chi,on the same side of the barrier. They had gone on a honeymoon. John's
experimental protocol would have to wait, and he was angry. Who had forgotten
to separate the dolphins on Friday afternoon? But everyone remembered that thedolphins had been separated and the door properly closed.
As a test, the experimenters repeated the conditions. Elvar and Chi-Chi wereseparated and the heavy door put in place amid Friday-afternoon ceremonies ofloud goodbyes, slammings of building doors, and the heavy trodding of exiting feet.

But the dolphins were being observed covertly. When all was quiet, they met atthe barrier and exchanged a few low-frequency creaking-door noises. Elvar thenpushed the door upward at one corner from his side until it wedged; Chi-Chi,from her side, pushed the opposite corner. Slowly, they worked the door up. Elvar
came swimming through and was received by the embraces ("enfinments" is not
the right word, either) of his mate. Then, according to John's story, those who lay
in waiting announced their presence by whistling, hooting, and booing –whereupon, with some appearance of embarrassment, Elvar swam to his half ofthe pool and the two dolphins worked down the vertical door from their opposite
sides.
This story has such an appealing human character to it – even down to a little
dollop of Victorian sexual guilt – that I find it unlikely. But there are many things
that are unlikely about dolphins.
I am probably one of the few people who has been "propositioned" by adolphin. The story requires a little background. I went to St. Thomas one winterto dive and to visit Lilly's dolphin station, which was then headed by Gregory
Bateson, an Englishman of remarkable and diverse interests in anthropology,
psychology, and human and animal behavior. Dining with some friends at a fairly
remote mountaintop restaurant, we engaged in casual conversation with thehostess at the restaurant, a young woman named Margaret. She described to me
how uneventful and uninteresting her days were (she was hostess only at night).
Earlier the same day Bateson had described to me his difficulties in finding
adequate research assistants for his dolphin program. It was not difficult to
introduce Margaret and Gregory to each other. Margaret was soon working withdolphins.
After Bateson left St. Thomas, Margaret was for a while de facto director of theresearch station. In the course of her work, Margaret performed a remarkable
experiment, described in some detail in Lilly's book The Mind of the Dolphin. She
began living on a kind of suspended raft over the pool of Peter the dolphin,spending twenty-four hours a day in close contact with him. Margaret's
experiment occurred not long before the incident I now speak of; it may have hadsomething to do with Peter's attitude toward me.
I was swimming in a large indoor pool with Peter. When I threw the pool's
rubber ball to Peter (as was natural for me to have done), he dove under the ballas it hit the water and batted it with his snout accurately into my hands. After a
few throws and precision returns, Peter's returns became increasingly inaccurate –forcing me to swim first to one side of the pool and then to the other in order toretrieve the ball. Eventually, it became clear that Peter chose not to place the ballwithin ten feet of me. He had changed the rules of the game.
Peter was performing a psychological experiment on me – to learn to what
extreme lengths I would go to continue this pointless game of catch. It was thesame kind of psychological testing that Elvar had conducted in our first meeting.
Such testing is one clue to the bond that draws dolphins to humans: We are one of
the few species that have pretensions of psychological knowledge; therefore, weare one of the few that would permit, however inadvertently, dolphins to perform
psychological experiments on us.
As in my first interview with Elvar, I eventually saw what was happening anddecided stoutly that no dolphin was going to perform a psychological experimenton me. So I held the ball and merely tread water. After a minute or so, Peter swam
rapidly toward me and made a grazing collision. He circled around and repeatedthis strange performance. This time I felt some protrusion of Peter's lightly
brushing my side as he passed. As he circled for a third pass, I idly wondered what
this protrusion might be. It was not his tail flukes, it was not … Suddenly it
dawned on me, and I felt like some maiden aunt to whom an improper proposal
had just been put. I was not prepared to cooperate, and all sorts of conventional
expressions came unbidden to my mind – like, "Don't you know any nice girldolphins?" But Peter remained cheerful and unoffended by my unresponsiveness.
(Is it possible, I now wonder, that he thought I was too dense to understand eventhat message?)Peter had been separated from female dolphins for some time and, in the not
too distant past, had spent many days in close contact, including sexual contact,with Margaret, another human being. I do not think that there is any sexual bondthat accounts for the closeness that dolphins feel toward humans, but the incident
had some significance. Even in what we piously describe as "bestiality" there are
only a few species which, so far as I have heard, are put upon by human beings forinterspecific sexual activities; these are entirely of the sort that humans havedomesticated. I wonder if some dolphins have thoughts about domesticating us.
Dolphin anecdotes make marvelous cocktail party accounts, an unending
source of casual conversation. One of the difficulties that I discovered withresearch into dolphin language and intelligence was precisely this fascination withanecdote; the really critical scientific tests were somehow never performed.
For example, I repeatedly urged that the following experiment be done:
Dolphin A is introduced into a tank that is equipped with two underwater audio
speakers. Each hydrophone is attached to an automatic fish dispenser catering tasty
dolphin fare. One speaker plays Bach, the other plays Beatles.

Which speaker is playing Bach or Beatles (a different composition each time) at
any given moment is determined randomly. Whenever Dolphin A goes to theappropriate speaker – let us say, the one playing Beatles – he is rewarded with afish. I think there is no doubt that any dolphin will – because of his great interestin, and facility with, the audio spectrum – be able soon to distinguish between
Bach and Beatles. But that is not the significant part of the experiment. What issignificant is the number of trials before Dolphin A becomes sophisticated – that
is, always knows that if he wishes a fish he should go to the speaker playing
Beatles.
Now Dolphin A is separated from the speakers by a barrier of plastic broadgauge mesh. He can see through the barrier, he can smell and taste through it, and,most important, he can hear and "speak" through it. But he cannot swim throughit. Dolphin B is then introduced into the area of the speakers. Dolphin B is naive;that is, he has had no prior experience with underwater fish dispensers, Bach, or
Beatles. Unlike the well-known difficulty in finding "naive" college students withwhom to perform experiments on cannibis sativa, there should be no difficultyfinding dolphins lacking extensive experience with Bach and Beatles. Dolphin B
must go through the same learning procedure as did Dolphin A. But now eachtime that Dolphin B (at first randomly) succeeds, not only does the dispenser
provide him with a fish, but a fish is also thrown to Dolphin A, who is able towitness the learning experience of Dolphin B. If Dolphin A is hungry, it isdistinctly to his advantage to communicate what he knows about Bach and Beatles
to Dolphin B. If Dolphin B is hungry, it is to his advantage to pay attention to theinformation that Dolphin A may have. The question, therefore, is: Does Dolphin B
have a steeper learning curve than Dolphin A? Does he reach the plateau ofsophistication in fewer trials or less time?
If such experiments were repeated many times and it were found that thelearning curves for Dolphin B were in a statistically significant sense always steeper
than those of Dolphin A, communication of moderately interesting information
between two dolphins would have been established. It might be a verbal
description of the difference between Bach and the Beatles – to my mind, adifficult but not impossible task – or it might simply be the distinction between
left and right in each trial, until Dolphin B catches on. This is not the bestexperimental design to test dolphin-to-dolphin communication, but it is typical ofa large category of experiments that could be performed. To my knowledge andregret, no such experiments have been performed with dolphins to date.
Questions of dolphin intelligence have taken on a special poignancy for me in
the past few years as the case of the humpback whale unfolded. In a remarkableset of experiments, Roger Payne, of Rockefeller University, has trailedhydrophones to a depth of tens of meters in the Caribbean, seeking and recording
the songs of the humpback whale. Another member, along with the dolphins, ofthe taxonomic class of Cetacea, the humpback whale has extraordinarily complex
and beautiful articulations, which carry over considerable distances beneath theocean surface, and which have an apparent social utility within and between
schools of whales, which are very gregarious social animals.
The brain size of whales is much larger than that of humans. Their cerebral
cortexes are as convoluted. They are at least as social as humans. Anthropologists
believe that the development of human intelligence has been critically dependent
upon these three factors: Brain volume, brain convolutions, and social interactions
among individuals. Here we find a class of animals where the three conditions
leading to human intelligence may be exceeded, and in some cases greatly
exceeded.
But because whales and dolphins have no hands, tentacles, or othermanipulative organs, their intelligence cannot be worked out in technology. Whatis left? Payne has recorded examples of very long songs sung by the humpback
whale; some of the songs were as long as half an hour or more. A few of themappear to be repeatable, virtually phoneme by phoneme; somewhat later theentire cycle of sounds comes out virtually identically once again. Some of the songs
have been commercially recorded and are available on CRM Records (SWR-II). I
calculate that the approximate number of bits (see Chapter 34) of information(individual yes/no questions necessary to characterize the song) in a whale song ofhalf an hour's length is between a million and a hundred million bits. Because of
the very large frequency variation in these songs, I have assumed that thefrequency is important in the content of the song – or, put another way, thatwhale language is tonal. If it is not as tonal as I guess, the number of bits in such asong may go down by a factor of ten. Now, a million bits is approximately the
number of bits in The Odyssey or the Icelandic Eddas. (It is also unlikely that in
the few hydrophone forays into Cetacean vocalizations that have been made todate, the longest of such songs has been recorded.)
Is it possible that the intelligence of Cetaceans is channeled into the equivalentof epic poetry, history, and elaborate codes of social interaction? Are whales anddolphins like human Homers before the invention of writing, telling of great deeds
done in years gone by in the depths and far reaches of the sea? Is there a kind of
Moby Dick in reverse – a tragedy, from the point of view of a whale, of acompulsive and implacable enemy, of unprovoked attacks by strange wooden andmetal beasts plying the seas and laden with humans?

The Cetacea hold an important lesson for us. The lesson is not about whales
and dolphins, but about ourselves. There is at least moderately convincing
evidence that there is another class of intelligent beings on Earth besides ourselves.
They have behaved benignly and in many cases affectionately toward us. We havesystematically slaughtered them. There is a monstrous and barbaric traffic in the
carcasses and vital fluids of whales. Oil is extracted for lipstick, industrial
lubricants and other purposes, even though this makes, at best, marginal economic
sense – there are effective substitute lubricants. But why, until recently, has there
been so little outcry against this slaughter, so little compassion for the whale?
Little reverence for life is evident in the whaling industry – underscoring a
deep human failing that is, however, not restricted to whales. In warfare, managainst man, it is common for each side to dehumanize the other so that there will
be none of the natural misgivings that a human being has at slaughtering another.
The Nazis achieved this goal comprehensively by declaring whole peoples
untermenschen, subhumans. It was then permissible, after such reclassification, todeprive these peoples of civil liberties, enslave them, and murder them. The Nazis
are the most monstrous, but not the most recent, example. Many other cases
could be quoted. For Americans, covert reclassifications of other peoples asuntermenschen has been the lubricant of military and economic machinery, fromthe early wars against the American Indians to our most recent military
involvements, where other human beings, military adversaries but inheritors of anancient culture, are decried as gooks, slopeheads, slanteyes, and so on – a litany ofdehumanization – until our soldiers and airmen could feel comfortable atslaughtering them.
Automated warfare and aerial destruction of unseen targets make suchdehumanization all the easier. It increases the "efficiency" of warfare because it
undercuts our sympathies with our fellow creatures. If we do not see whom wekill, we feel not nearly so bad about murder. And if we can so easily rationalize
the slaughter of others of our own species, how much more difficult will it be tohave a reverence for intelligent individuals of different species?
It is at this point that the ultimate significance of dolphins in the search forextraterrestrial intelligence emerges. It is not a question of whether we are
emotionally prepared in the long run to confront a message from the stars. It iswhether we can develop a sense that beings with quite different evolutionary
histories, beings who may look far different from us, even "monstrous," may,nevertheless, be worthy of friendship and reverence, brotherhood and trust. We
have far to go; while there is every sign that the human community is moving inthis direction, the question is, are we moving fast enough? The most likely contact

with extraterrestrial intelligence is with a society far more advanced than we(Chapter 31). But we will not at any time in the foreseeable future be in theposition of the American Indians or the Vietnamese – colonial barbarity practiced
on us by a technologically more advanced civilization – because of the great spaces
between the stars and what I believe is the neutrality or benignness of any
civilization that has survived long enough for us to make contact with it. Nor will
the situation be the other way around, terrestrial predation on extraterrestrial
civilizations – they are too far away from us and we are relatively powerless.
Contact with another intelligent species on a planet of some other star – a species
biologically far more different from us than dolphins or whales – may help us tocast off our baggage of accumulated jingoisms, from nationalism to humanchauvinism. Though the search for extraterrestrial intelligence may take a very
long time, we could not do better than to start with a program of rehumanization
by making friends with the whales and the dolphins.

Chapter 25: "Hello, Central Casting? Send Me Twenty Extraterrestrials"
My friend Arthur C. Clarke had a problem. He was writing a major motion
picture with Stanley Kubrick of Dr. Strangelove fame. It was to be called Journey
Beyond the Stars, and a small crisis in the story development had arisen. Could I
have dinner with them at Kubrick's New York penthouse and help adjudicate thedispute? (The film's title, by the way, seemed a little strange to me. As far as I
knew, there is no place beyond the stars. A film about such a place would have to
be two hours of blank screen – a possible plot only for Andy Warhol. I was surethat was not what Kubrick and Clarke had in mind.)
After a pleasant dinner, the crisis emerged as follows: About midway throughthe movie, a manned space vehicle is making a close approach to either Jupiter 5,
the innermost satellite of Jupiter, or to Iapetus, one of the middle-sized satellites
of Saturn. As the spacecraft approaches and the curvature of the satellite is visibleon the screen, we become aware that the satellite is not a natural moon. It is an
artifact of some immensely powerful, advanced civilization. Suddenly, an apertureappears in the side of the satellite; through it we see – stars. But they are not thestars on the other side of the satellite. They are a portion of the sky from
elsewhere. Small drone rockets are fired into the aperture, but contact with themis lost as soon as they pass through. The aperture is a space gate, a way to get fromone part of the universe to another without the awkwardness of traversing theintervening distance. The spacecraft plunges through the gate and emerges in thevicinity of another stellar system, with a red giant star blazing in the sky. Orbiting
the red giant is a planet, obviously the site of an advanced technologicalcivilization. The spacecraft approaches the planet, makes landfall, and then –what?
Although the human elements were nearing studio production in England, thisfairly important plot line – the ending! – had not yet been worked out by the two
authors. The spacecraft's crew, or some fraction of it, was to make contact withextraterrestrials. Yes, but how to portray the extraterrestrials? Kubrick favored
extraterrestrials not profoundly different from human beings. Kubrick's preference
had one distinct advantage, an economic one: He could call up Central Casting andask for twenty extraterrestrials. With a little makeup, he would have his problem
solved. The alternative portrayal of extraterrestrials, whatever it was, was boundto be expensive.
I argued that the number of individually unlikely events in the evolutionary
history of Man was so great that nothing like us is ever likely to evolve again
anywhere else in the universe. I suggested that any explicit representation of anadvanced extraterrestrial being was bound to have at least an element of falsenessabout it, and that the best solution would be to suggest, rather than explicitly todisplay, the extraterrestrials.
The film, subsequently titled 2001: A Space Odyssey, opened three years later.
At the premiere, I was pleased to see that I had been of some help. As we learn
from Jerome Agel's book The Making of Kubrick's "2001" (Signet, 1970), Kubrickexperimented during production with many representations of extraterrestrial life,
including a pirouetting dancer in black tights with white polka dots. Photographedagainst a black background, this would have been visually very effective. He finallydecided on a surrealistic representation of extraterrestrial intelligence. The movie
has played a significant role in expanding the average person's awareness of thecosmic perspective. Many Soviet scientists consider 2001 to be the best American
movie they have seen. The extraterrestrial ambiguities did not bother them at all.
During the filming of 2001, Kubrick, who obviously has a grasp for detail,became concerned that extraterrestrial intelligence might be discovered before the$10.5 million film was released, rendering the plot line obsolete, if not erroneous.
Lloyd's of London was approached to underwrite an insurance policy protecting
against losses should extraterrestrial intelligence be discovered. Lloyd's of London,
which insures against the most implausible contingencies, declined to write such a
policy. In the mid-1960s there was no search being performed for extraterrestrial
intelligence, and the chance of accidentally stumbling on extraterrestrial
intelligence in a few years' period was extremely small. Lloyd's of London missed agood bet.

Chapter 26: The Cosmic Connection
From earliest times, human beings have pondered their place in the universe.
They have wondered whether they are in some sense connected with the
awesome and immense cosmos in which the Earth is imbedded.
Many thousands of years ago a pseudoscience called astrology was invented.
The positions of the planets at the birth of a child were supposed to play a majorrole in determining his or her future. The planets, moving points of light, were
thought, in some mysterious sense, to be gods. In his vanity, Man imagined theuniverse designed for his benefit and organized for his use.
Perhaps the planets were identified with gods because their motions seemed
irregular. The word "planet" is Greek for wanderer. The unpredictable behavior of
the gods in many legends may have corresponded well with the apparently
unpredictable motions of the planets. The argument may have been: Gods don't
follow rules; planets don't follow rules; planets are gods.
When the ancient priestly astrological caste discovered that the motions of theplanets were not irregular but predictable, they seem to have kept thisinformation to themselves. No use unnecessarily worrying the populace,undermining religious belief, and eroding the supports of political power.
Moreover, the Sun was the source of life. The Moon, through the tides, dominatedagriculture – especially in river basins like the Indus, the Nile, the Yangtze, andthe Tigris-Euphrates. How reasonable that these lesser lights, the planets, shouldhave a subtler but no less definite influence on human life!
The search for a connection, a hooking-up between people and the universe,
has not diminished since the dawn of astrology. The same human needs exist
despite the advances of science.
We now know that the planets are worlds more or less like our own. We
know that their light and gravity have negligible influence on a newborn babe. We
know that there are enormous numbers of other objects – asteroids, comets,
pulsars, quasars, exploding galaxies, black holes, and the rest – objects not known
to the ancient speculators who invented astrology. The universe is immensely
grander than they could have imagined.
Astrology has not attempted to keep pace with the times. Even the calculationsof planetary motions and positions performed by most astrologers are usuallyinaccurate.

No study shows a statistically significant success rate in predicting throughtheir horoscopes the futures or the personality traits of newborn children. There isno field of radio-astrology or X-ray astrology or gamma-ray astrology, taking
account of the energetic new astronomical sources discovered in recent years.
Nevertheless, astrology remains immensely popular everywhere. There are atleast ten times more astrologers than astronomers. A large number, perhaps amajority, of newspapers in the United States have daily columns on astrology.
Many bright and socially committed young people have more than a passing
interest in astrology. It satisfies an almost unspoken need to feel a significance forhuman beings in a vast and awesome cosmos, to believe that we are in some way
hooked up with the universe – an ideal of many drug and religious experiences,
the samadhi of some Eastern religions.
The great insights of modern astronomy have shown that, in some senses quite
different from those imagined by the earlier astrologers, we are connected up withthe universe.
The first scientists and philosophers – Aristotle, for example – imagined thatthe heavens were made of a different sort of material than the Earth, a special kindof celestial stuff, pure and undefiled. We now know that this is not the case.
Pieces of the asteroid belt called meteorites; samples of the Moon returned by
Apollo astronauts and Soviet unmanned spacecraft; the solar wind, which expands
outward past our planet from the Sun; and the cosmic rays, which are probably
generated from exploding stars and their remnants – all show the presence of thesame atoms we know here on Earth. Astronomical spectroscopy is able todetermine the chemical composition of collections of stars billions of light-years
away. The entire universe is made of familiar stuff. The same atoms and molecules
occur at enormous distances from Earth as occur here within our Solar System.
These studies have yielded a remarkable conclusion. Not only is the universe
made everywhere of the same atoms, but the atoms, roughly speaking, are present
everywhere in approximately the same proportions.
Almost all the stuff of the stars and the interstellar matter between the stars ishydrogen and helium, the two simplest atoms. All other atoms are impurities,
trace constituents. This is also true for the massive outer planets of our Solar
System, like Jupiter. But it is not true for the comparatively tiny hunks of rock andmetal in the inner part of the Solar System, like our planet Earth. This is because
the small terrestrial planets have gravities too weak to hold their original hydrogenand helium atmospheres, which have slowly leaked away to space.
The next most abundant atoms in the universe turn out to be oxygen, carbon,

nitrogen, and neon. These are atoms everyone has heard of. Why are thecosmically most abundant elements those that are reasonably common on Earth –rather than, say, yttrium or praseodymium?
The theory of the evolution of stars is sufficiently advanced that astronomers
are able to understand the various kinds of stars and their relations – how a star isborn from the interstellar gas and dust, how it shines and evolves bythermonuclear reactions in its hot interior, and how it dies. These thermonuclear
reactions are of the same sort as the reactions that underlie thermonuclear
weapons (hydrogen bombs): The conversion of four atoms of hydrogen into one ofhelium.
But in the later stages of stellar evolution, higher temperatures are reached in
the insides of stars, and elements heavier than helium are generated bythermonuclear processes. Nuclear astrophysics indicates that the most abundant
atoms produced in such hot red giant stars are precisely the most abundant atoms
on Earth and elsewhere in the universe. The heavy atoms generated in the insidesof red giants are spewed out into the interstellar medium, by slow leakage fromthe star's atmosphere like our own solar wind, or by mighty stellar explosions,some of which can make a star a billion times brighter than our Sun.
Recent infrared spectroscopy of hot stars has discovered that they are blowing
off silicates into space – rock powder spewed out into the interstellar medium.
Carbon stars probably expel graphite particles into surrounding cosmic space.
Other stars shed ice. In their early histories, stars like the Sun probably propelledlarge quantities' of organic compounds into interstellar space; indeed, simple
organic molecules are found by radio astronomical methods to be filling the space
between the stars. The brightest planetary nebula known (a planetary nebula is an
expanding cloud usually surrounding an exploding star called a nova) seems tocontain particles of magnesium carbonate: Dolomite, the stuff of the European
mountains of the same name, expelled by a star into interstellar space.
These heavy atoms – carbon, nitrogen, oxygen, silicon, and the rest – then float
about in the interstellar medium until, at some later time, a local gravitationalcondensation occurs and a new sun and new planets are formed. This secondgeneration solar system is enriched in heavy elements.
The fate of individual human beings may not now be connected in a deep way
with the rest of the universe, but the matter out of which each of us is made is
intimately tied to processes that occurred immense intervals of time andenormous distances in space away from us. Our Sun is a second- or third-generation star. All of the rocky and metallic material we stand on, the iron in our
blood, the calcium in our teeth, the carbon in our genes were produced billions ofyears ago in the interior of a red giant star. We are made of star-stuff.
Our atomic and molecular connection with the rest of the universe is a real andunfanciful cosmic hookup. As we explore our surroundings by telescope and spacevehicle, other hookups may emerge. There may be a network ofintercommunicating extraterrestrial civilizations to which we may link up
tomorrow, for all we know. The undelivered promise of astrology – that the stars
impel our individual characters – will not be satisfied by modern astronomy. But
the deep human need to seek and understand our connection with the universe isa goal well within our grasp.

Chapter 27: Extraterrestrial Life: An Idea Whose Time Has Come
Thousands of years ago, the idea that the planets were populated by intelligent
beings was uncommon. The idea was that the planets themselves were intelligent
beings. Mars was the god of war, Venus was the goddess of beauty, Jupiter was the
king of the gods.
In early Roman times a few writers, for example Lucian of Samasota, conceived
that at least the Moon was a place that was populated as the Earth was. Hisscience-fiction story describing travel to the Moon was called the "True History."
It was, of course, false.
The idea of the planets as an elegant celestial clockwork created by the Deityfor the amazement and utility of men emerged in the Renaissance. In the year
1600 Giordano Bruno was burned to death at the stake, in part for uttering andpublishing the heresy that there were other worlds and other beings inhabitingthem.
The pendulum swung far in the other direction in subsequent centuries.
Writers such as Bernard de Fontenelle, Emanuel Swedenborg, and even ImmanuelKant and Johannes Kepler could safely imagine that perhaps all the planets were
inhabited. Indeed, the idea was expressed that the name of the planet gave somehint to the character of its inhabitants. The denizens of Venus were amorous;
those of Mars, warlike or martial; the inhabitants of Mercury, fickle or mercurial;
those of Jupiter, jolly or jovial. And so on. The great British astronomer William
Herschel even supposed that the Sun was inhabited.
But as the extremes of the physical environments in the Solar System became
clearer and the exquisite adaptation to the environment of organisms on Earthbecame more apparent, skeptics arose. Perhaps Mars and Venus were inhabited,
but surely not Mercury, not the Moon, not Jupiter. And so on.
In the last few decades of the nineteenth century the observations of the planet
Mars by Giovanni Schiaparelli and Percival Lowell quickened public excitement
about the possibility of intelligence on our planetary neighbor. Lowell's passion for
the idea of intelligent beings on Mars, his articulateness, and the wide publicationof his books did much to bring this idea to the public attention, as did sciencefiction writers who followed the Lowellian scenario.
But as the evidence for intelligent life on Mars withered, and as theenvironment of Mars was perceived to be more and more inclement by terrestrial

standards, popular enthusiasm for the idea waned.
By then, scientific interest in extraterrestrial life had reached a nadir. The very
enthusiasm with which Lowell pursued the idea of intelligent beings on Mars andthe attention that these ideas received from the man in the street repelled many
scientists. In addition, a new astronomical field, astrophysics, the application ofphysics to the surfaces and interiors of stars, had achieved phenomenal success, 151
and the brightest and most enthusiastic young astronomers went into stellar
astronomy rather than planetary studies. The pendulum had swung so far that in
the period just after the Second World War, there was – in all of the United States– only one astronomer doing serious physical investigations of the planets, G. P.
Kuiper, then of the University of Chicago. Not only had astronomers been turned
off extraterrestrial life, they had been turned off planetary studies in general.
Since 1950, the situation has slowly reversed again; the pendulum is once more
swinging. The development of new measuring instruments (a by-product ofWorld War II), at first ground-based and then, more important, space-borne, hasproduced a massive infusion of basic new knowledge about the physicalenvironments of the Moon and planets. Young scientists have again been attracted
to planetary studies, not only astronomers, but also geologists, chemists, physicists,
and biologists. The discipline needs them all.
We now know that the building blocks for the origin of life are in the cards ofphysics and chemistry; whenever standard primitive atmospheres are exposed tocommon energy sources, the building blocks of life on Earth drop out of theatmosphere in times of days or weeks. Organic compounds have been found inmeteorites and in interstellar space. Small quantities have been found even in suchan inhospitable environment as the Moon. They are suspected to exist in Jupiter,in the outer planets of the Solar System, as well as on Titan, the largest moon of
Saturn. Both theory and observation now suggest that planets are a common, if notinvariable, accompaniment of stars, rather than an exceedingly rare occurrence, as
was fashionable to believe in the first decades of this century (see pages 192 and193).
We now have, for the first time, the tools to make contact with civilizations onplanets of other stars. It is an astonishing fact that the great one-thousand-footdiameter radio telescope of the National Astronomy and Ionosphere Center, run
by Cornell University in Arecibo, Puerto Rico, would be able to communicate
with an identical copy of itself anywhere in the Milky Way Galaxy. We have at
our command the means to communicate not merely over distances of hundreds
or thousands of light-years; we can communicate over tens of thousands of lightyears, into a volume containing hundreds of billions of stars. The hypothesis that

advanced technical civilizations exist on planets of other stars is amenable toexperimental testing. It has been removed from the arena of pure speculation. It is
now in the arena of experiment.
Our first attempt to listen to broadcasts from extraterrestrial societies was
Project Ozma. Organized by Frank Drake in 1960 at the National Radio
Astronomy Observatory (NRAO), it looked at two stars at one frequency for two
weeks. The results were negative. Slightly more ambitious projects are, at the timeof writing, being performed at the Gorky Radiophysical Institute in the Soviet
Union and at NRAO in the United States. All in all, perhaps a few hundred
nearby stars will be examined at one or two frequencies. But even the most
optimistic calculations on the distances to the nearest stars suggest that hundredsof thousands to millions of stars must be examined before an intelligible signal
from one of them will be received. This requires a large effort covering a sizable
period of time. But it is well within our resources, our abilities, and our interests.
The change in the climate of opinion about extraterrestrial life was reflected in1971 by a scientific conference held in Byurakan, Soviet Armenia, and sponsoredjointly by the Soviet Academy of Sciences of the U.S.S.R. and the National
Academy of Sciences of the United States. I had the privilege of chairing the U.S.
delegation to this meeting. The participants represented astronomy, physics,
mathematics, biology, chemistry, archaeology, anthropology, history, electronics,
computer technology, and cryptography. The group, which included two skepticalNobel laureates, was marked for its crossing of national as well as disciplinary
boundaries. The conference concluded that the chances of there being
extraterrestrial communicative societies and our present technological ability tocontact them were both sufficiently high that a serious search was warranted.
Some of the specific conclusions that were reached were these:
1. The striking discoveries of recent years in the fields of astronomy, biology,
computer science and radiophysics have transferred some of the problems ofextraterrestrial civilizations and their detection from the realm of speculation to a
new realm of experiment and observation. For the first time in human history, it
has become possible to make serious and detailed experimental investigations of
this fundamental and important problem.
2. This problem may prove to be of profound significance for the future
development of Mankind. If extraterrestrial civilizations are ever discovered, theaffect on human scientific and technological capabilities will be immense, and thediscovery can positively influence the whole future of Man. The practical andphilosophical significance of a successful contact with an extraterrestrial
civilization would be so enormous as to justify the expenditure of substantial

efforts. The consequences of such a discovery would greatly add to the total of
human knowledge.
3. The technological and scientific resources of our planet are already large
enough to permit us to begin investigations directed towards the search forextraterrestrial intelligence. As a rule, such studies should provide importantscientific results even when specific searches for extraterrestrial intelligence do not
succeed. At present, these investigations can be carried out effectively in thevarious countries by their own scientific institutions. Even at this early stage,
however, it would be useful to discuss and coordinate specific programs ofresearch and to exchange scientific information. In the future, it would bedesirable to combine the efforts of investigators in various countries to achieve theexperimental and observational objectives. It seems to us appropriate that the
search for extraterrestrial intelligence should be made by representatives of thewhole of mankind.
4. Various modes of search for extraterrestrial intelligence were discussed indetail at the Conference. The realization of the most elaborate of these proposals
would require considerable time and effort and an expenditure of funds
comparable to the funds devoted to space and nuclear research. Useful searches
can, however, also be initiated at a very modest scale.
5. The Conference participants consider highly valuable present andforthcoming space-vehicle experiments directed towards searching for life on theother planets of our solar system. They recommend the continuation andstrengthening of work in such areas as prebiological organic chemistry, searches for
extrasolar planetary systems, and evolutionary biology, which bear sharply on the
problem.
6. The Conference recommends the initiation of specific new investigations
directed towards modes of search for signals.
(The complete Proceedings of the conference are published as Communication
with Extraterrestrial Intelligence, Carl Sagan, ed., Cambridge, Massachusetts, The
M.I.T. Press, 1973.)
Another sign of the increasing acceptability of the search for extraterrestrial
intelligence is the recommendations of the Astronomy Survey Committee of the
U. S. National Academy of Sciences, which had been asked to summarize theneeds of astronomy in the decade of the 1970s. The Committee's report was thefirst such national report on the future of astronomy to lay stress on the search forextraterrestrial intelligence – as a possibly important by-product of astronomical
research in the near future and as a justification for the construction of large radio
telescopes.
Nearer to home, there is an accelerating set of laboratory studies of the originof life on Earth. If the origin of life on Earth turns out to have been exceedingly"easy," the chances of life elsewhere are correspondingly high.
There is also a concerted effort in the United States – Project Viking – to land
instrumented payloads on the surface of Mars to search for indigenous life forms.
The idea of extraterrestrial life is an idea whose time has come.

Chapter 28: Has the Earth Been Visited?
By far the cheapest way of communicating with the Earth, if you're arepresentative of an advanced extraterrestrial civilization, is by radio. A single bitof radio information, sent winging across space to the Earth, would cost far lessthan a penny. A radio search for extraterrestrial intelligence seems, therefore, avery reasonable place for us to begin. But should we not examine otherpossibilities closer to home? Wouldn't we look silly if we expended a major effort
listening for radio messages or searching for life on Mars if, all the while, there washere on Earth evidence of extraterrestrial life?
There are two hypotheses of this sort that have gained a following in the
popular literature. The first postulates that the Earth is today being visited by
spacecraft from other worlds – this is the extraterrestrial flying saucer orunidentified flying object (UFO) hypothesis. The second also postulates that the
Earth has been visited by such spacecraft, but in the past, before written history.
The extraterrestrial hypothesis of UFO origins is a complex subject, powerfully
dependent on the reliability of witnesses. A comprehensive discussion of thisproblem has recently been published in UFO's: A Scientific Debate (Carl Sagan andThornton Page, editors, Ithaca, N.Y., Cornell University Press, 1972), in which allsides of the subject have been aired. My own view is that there are no cases thatare simultaneously very reliable (reported independently by a large number of
witnesses) and very exotic (not explicable in terms of reasonably postulated
phenomena – as a strange moving light could be a searchlight from a weather
airplane or a military aerial refueling operation). There are no reliably reported
cases of strange machines landing and taking off, for example.
There is another approach to the extraterrestrial hypothesis of UFO origins.
This assessment depends on a large number of factors about which we know little,
and a few about which we know literally nothing. I want to make some crude
numerical estimate of the probability that we are frequently visited byextraterrestrial beings.
Now, there is a range of hypotheses that can be examined in such a way. Letme give a simple example: Consider the Santa Claus hypothesis, which maintains
that, in a period of eight hours or so on December 24-25 of each year, an out-sized
elf visits one hundred million homes in the United States. This is an interesting
and widely discussed hypothesis. Some strong emotions ride on it, and it is argued
that at least it does no harm.
We can do some calculations. Suppose that the elf in question spends one

second per house. This isn't quite the usual picture – "Ho, Ho, Ho," and so on –but imagine that he is terribly efficient and very speedy; that would explain why
nobody ever sees him very much – only one second per house, after all. With ahundred million houses he has to spend three years just filling stockings. I haveassumed he spends no time at all in going from house to house. Even withrelativistic reindeer, the time spent in a hundred million houses is three years andnot eight hours. This is an example of hypothesis-testing independent of reindeer
propulsion mechanisms or debates on the origins of elves. We examine thehypothesis itself, making very straightforward assumptions, and derive a result
inconsistent with the hypothesis by many orders of magnitude. We would thensuggest that the hypothesis is untenable.
We can make a similar examination, but with greater uncertainty, of theextraterrestrial hypothesis that holds that a wide range of UFOs viewed on theplanet Earth are space vehicles from planets of other stars. The report rates, atleast in recent years, have been several per day, at the very least. I will not makethat assumption. I will make the much more conservative assumption that one
such report per year corresponds to a true interstellar visitation. Let's see what this
implies.
We have to have some feeling for the number, N, of extant technicalcivilizations in the Galaxy – that is, civilizations vastly in advance of our own,
civilizations that are able, by whatever means, to perform interstellar space flight.
(While the means are difficult, they don't enter into this discussion, just as
reindeer propulsion mechanisms don't affect our discussion of the Santa Claus
hypothesis.)
An attempt has been made to specify explicitly the factors that enter adetermination of the number of such technical civilizations in the Galaxy. I will
not here run through what numbers have been assigned to the various quantities
involved – it's a multiplication of many probabilities, and the likelihood that we
can make a good judgment decreases as we proceed down the list. N depends firston the mean rate at which stars are formed in the Galaxy, a number that is known
reasonably well. It depends on the number of stars that have planets, which is lesswell known, but there are some data on that. It depends on the fraction of suchplanets that are so suitably located with respect to their star that the environmentis a feasible one for the origin of life. It depends on the fraction of such otherwise
feasible planets on which the origin of life, in fact, occurs. It depends on thefraction of those planets on which the origin of life occurs in which, after life hasarisen, an intelligent form comes into being. It depends on the fraction of thoseplanets in which intelligent forms have arisen that evolve a technical civilization

substantially in advance of our own. And it depends on the average lifetime ofsuch a technical civilization.
It is clear that we are rapidly running out of examples as we go farther andfarther along. We have many stars, but only one instance of the origin of life, andonly a very limited number – some would say only one – of instances of theevolution of intelligent beings and technical civilizations on this planet. And wehave no cases whatever to make a judgment on the mean lifetime of a technicalcivilization. Nevertheless, there is an entertainment that some of us have been
engaged in, making our best estimates about these numbers and coming out with avalue of N. The result that emerges is that N roughly equals one tenth the average
lifetime of a technical civilization in years.
If we put in a number like ten million years for the average lifetime ofadvanced technical civilizations, we come out with a number for such technicalcivilizations in the Galaxy of about a million – that is, a million other stars
with planets on which today there are advanced civilizations. This is quite adifficult calculation to do accurately. The choice of ten million years for the
average lifetime of a technical civilization is rather optimistic. But let's take these
optimistic numbers and see where they lead us.
Let's assume that each of these million technical civilizations launches Q
interstellar space vehicles a year, so that
Q interstellar space vehicles are launched per year. Let's assume that there's
only one contact made per journey. In the steady-state situation, there aresomething like Q arrivals somewhere or other per year. Now, there surely aresomething like 1010 interesting places in the Galaxy to go visit (we have several
times 1011 stars) and, therefore, an average of 1/104=10–4 arrivals at a given
interesting place (let's say a planet) per year. So if only one UFO is to visit the Eartheach year, we can calculate what mean launch rate is required at each of these million
worlds. The number turns out to be ten thousand launches per year per civilization,and ten billion launches in the Galaxy per year. This seems excessive. Even if we imagine a
civilization much more advanced than ours, to launch ten thousand such vehicles for
only one to appear here is probably asking too much. And if we were more pessimisticon the lifetime of advanced civilizations, we would require a proportionately larger
launch rate. But as the lifetime decreases, the probability that a civilization would
develop interstellar flight very likely decreases as well.
There is a related point made by the American physicist Hong-Yee Chiu; hetakes more than one UFO arriving at Earth per year, but his argument follows
along the same lines as the one I have just presented. He calculates the total massof metals involved in all of these space vehicles during this history of the Galaxy.

The vehicle has to be of some size – it should be bigger than the Apollo capsule,let's say – and we can calculate how much metal is required. It turns out that the
total mass of half a million stars has to be processed and all their metals extracted.
Or if we extend the argument and assume that only the outer few hundred miles
or so of stars like the Sun can be mined by advanced technologies (farther in, it's
too hot), we find that two billion such stars must be processed, or about 1 percentof the stars in the Galaxy. This also sounds unlikely.
Now you may say, "Well, that's a very parochial approach; maybe they haveplastic spaceships." Yes, I suppose that's possible. But the plastic has to come fromsomewhere, and plastics vs. metals changes the conclusions very little. This
calculation gives some feeling for the magnitude of the task when we are asked tobelieve that there are routine and frequent interstellar visits to our planet.
What about possible counterarguments? For example, it might be argued that
we are the object of special attention – we have just developed all sorts of signs ofcivilization and high intelligence like nuclear weapons, and maybe, therefore, weare of particular interest to interstellar anthropologists. Perhaps. But we have only
signaled the presence of our technical civilization in the past few decades. The
news can be only some tens of light-years from us. Also, all the anthropologists inthe world do not converge on the Andaman Islands because the fish net has justbeen invented there. There are a few fish net specialists and a few Andamanspecialists; and these guys say, "Well, there's something terrific going on in the
Andaman Islands. I've got to spend a year there right away because if I don't go
now, I'll miss out." But the pottery experts and the specialists in Australianaborigines don't pack up their bags and leave for the Indian Ocean.
To imagine that there is something absolutely fascinating about what ishappening right here is precisely contrary to the idea that there are lots ofcivilizations around. Because if the latter is true, the development of our sort ofcivilization must be pretty common. And if we are not pretty common, then there
are not going to be many civilizations advanced enough to send visitors.
Even so, is it not possible that the second UFO hypothesis is true – that inhistorical or recent prehistoric times an extraterrestrial space vehicle made landfall
on Earth? There is surely no way in which we can exclude such a contingency.
How could we prove it?
A number of popular books have recently been written that allege todemonstrate such a visitation. The arguments are of two sorts, legend and artifact.
I broached this subject in the book Intelligent Life in the Universe, written with theSoviet astrophysicist I. S. Shklovskii and published in 1966. I examined a typicallegend suggestive of contact between our ancestors and an apparent representativeof a superior society. The legend, taken from the earliest Sumerian mythology, is
important because the Sumerians are the direct cultural antecedents of our own
civilization. A superior being was supposed to have taught the Sumerians
mathematics, astronomy, agriculture, social and political organization, and written
language – all the arts necessary for making the transition from a hunter-gatherer
society to the first civilization.
But as provocative as this and similar legends were, I concluded that it was
impossible to demonstrate extraterrestrial contact from such legends: There areplausible alternative explanations. We can understand why priests might makemyths about superior beings who inhabit the skies and give directions to humanbeings on how to order their affairs. Among other "advantages," such legends
permit the priests to control the people.
There is only one category of legend that would be convincing: When
information is contained in the legend that could not possibly have been generated
by the civilization that created the legend – if, for example, a number transmitted
from thousands of years ago as holy turns out to be the nuclear fine structure
constant. This would be a case worthy of some considerable attention.
Also convincing would be a certain class of artifact. If an artifact of technology
were passed on from an ancient civilization – an artifact that is far beyond thetechnological capabilities of the originating civilization – we would have aninteresting prima facie case for extraterrestrial visitation. An example would be an
illuminated manuscript, rescued from an Irish monastery, that contains theelectronic circuit diagram for a superheterodyne radio receiver. Great care would
have to be taken about the provenance of this artifact, just as art collectors are
cautious about a newly discovered Raphael. We would make sure that nocontemporary Irish prankster was the source of the circuit diagram.
To the best of my knowledge, there are no such legends and no such artifacts.
All the ancient artifacts put forward, for example, by Erik von Danniken in his
book Chariots of the Gods? have a variety of plausible, alternative explanations.
Representations of beings with large, elongated heads, alleged to resemble space
helmets, could equally well be inelegant artistic renditions, depictions of
ceremonial head masks or expressions of rampant hydrocephalia. In fact, theexpectation that extraterrestrial astronauts would look precisely like American orSoviet astronauts, down to their space suits and eyeballs, is probably less credible
than the idea of a visitation itself. Likewise, the idea expressed by von Danniken

and others that ancient astronauts erected airfields, employed rockets, andexploded nuclear weapons on Earth is implausible in the extreme, precisely
because we ourselves have just developed this technology. A visitor from space
will not be so close to us in time. It is as if, framing such an idea in 1870, weconcluded that extraterrestrials use hot-air balloons for space exploration. Far
from being too daring, such ideas are stodgy in their unimaginativeness. Most
popular accounts of alleged contact with extraterrestrials are strikingly
chauvinistic.
An American author named Richard Shaver claims that ordinary rocks, sliced
fine, contain a set of still photographs left by an ancient civilization, which can be
run as a movie film. Just pick up any rock and slice it fine, he says.
In the great high plain of Nasca in Peru, there is a set of enormous geometricalfigures. They are quite difficult to discern when standing among them, but quite
discernible from the air. It is easy to see how an early human civilization could
have made such figures. But why, it is asked, should such constructs be madeexcept for or by an extraterrestrial civilization? If people believe in the existenceof gods in the sky, it is not straining credulity to imagine them making messages tocommunicate with those gods. The markings may be a kind of collective graphicalprayer. But they do not necessarily demonstrate the reality of the intended
recipient of the prayer.
There are other cases that seem to be quite convincing at first, such as aperfectly machined steel cube, said to reside in the Salzburg Museum and to havebeen recovered from geological strata millions of years old, or the receipt of the
television call signals of a television station off the air for three years. These cases
are almost certainly hoaxes.
There are equally provocative archaeological circumstances that the writers ofsuch sensational books have somehow missed. For example, in the frieze of thegreat Aztec pyramids at San Juan Teotihuacan, outside Mexico City, there is arepeated figure, described as a rain god, but looking for all the world like anamphibious tracked vehicle with four headlights (see page 201). I do not for a
moment believe that such amphibious vehicles were indigenous in Aztec times –among other reasons, because they are too close to what we have today rather
than too far from it.
These artifacts are, in fact, psychological projective tests. People can see inthem what they wish. There is nothing to prevent anyone from seeing signs of past
extraterrestrial visitations all about him. But to a person with an even mildly
skeptical mind, the evidence is unconvincing. Because the significance of such adiscovery would be so enormous, we must employ the most critical reasoning andthe most skeptical attitudes in approaching such data. The data do not pass suchtests. Pondering wall paintings, for this purpose, like looking for UFOs, remains an
unprofitable investment of terrestrial intelligence – if we are truly interested in thequest for extraterrestrial intelligence.

Chapter 29: A Search Strategy for Detecting Extraterrestrial Intelligence
Suppose we have arranged a meeting at an unspecified place in New York City
with a stranger we have never met and about whom we know nothing – a rather
foolish arrangement, but one that is useful for our purposes. We are looking for
him, and he is looking for us. What is our search strategy? We probably would notstand for a week on the corner of Seventy-eighth Street and Madison Avenue.
Instead, we would recall that there are a number of widely known landmarks in
New York City – as well known to the stranger as to us. He knows we know
them, we know he knows we know them, and so on. We then shuttle among
these landmarks: The Statue of Liberty, the Empire State Building, Grand Central
Station, Radio City Music Hall, Lincoln Center, the United Nations, Times Square,and just conceivably, City Hall. We might even indulge ourselves in a few lesslikely possibilities, such as Yankee Stadium or the Manhattan entrance to theStaten Island Ferry. But there are not an infinite number of possibilities. There are
not millions of possibilities; there are only a few dozen possibilities, and in time
we can cover them all.
The situation is just the same in the frequency-search strategy for interstellar
radio communication. In the absence of any prior contact, how do we know
precisely where to search? How do we know which frequency or "station" to tune
in on? There are at least millions of possible frequencies with reasonable radio
bandpasses. But a civilization interested in communicating with us shares with us acommon knowledge about radio astronomy and about our Galaxy. They know, forexample, that the most abundant atom in the universe, hydrogen, characteristicallyemits at a frequency of 1,420 Megahertz. They know we know it. They know weknow they know it. And so on. There are a few other abundant interstellar
molecules, such as water or ammonia, which have their own characteristicfrequencies of emission and absorption. Some of these lie in a region of the galactic
radio spectrum where there is less background noise than others. This is also
shared information. Students of this problem have come up with a short list of
possibly a dozen frequencies that seem to be the obvious ones to examine. It iseven conceivable that water-based life will communicate at water frequencies,
ammonia-based life at ammonia frequencies, etc.
There appears to be a fair chance that advanced extraterrestrial civilizations are
sending radio signals our way, and that we have the technology to receive suchsignals. How should a search for these signals be organized? Existing radio
telescopes, even very small ones, would be adequate for a preliminary search.
Indeed, the ongoing search at the Gorky Radiophysical Institute, in the Soviet
Union, involves telescopes and instrumentation that are quite modest bycontemporary standards.
The amiable and capable president of the Soviet Academy of Sciences, M. V.
Keldysh, once told me, with a twinkle in his eye, that "when extraterrestrial
intelligence is discovered, then it will become an important scientific problem." Aleading American physicist has argued forcefully with me that the best method tosearch for extraterrestrial intelligence is simply to do ordinary astronomy; if the
discovery is to be made, it will be made serendipitously. But it seems to me that
we can do something to enhance the likelihood of success in such a search, andthat the ordinary pursuit of radio astronomy is not quite the same as an explicit
search of certain stars, frequencies, bandpasses, and time constants for
extraterrestrial intelligence.
But there are enormous numbers of stars to investigate, and many possible
frequencies. A reasonable search program will almost certainly be a very long one.
Such a search, using a large telescope full time, should take at least decades, byconservative estimates. The radio observers in such an enterprise, no matter how
enthusiastic they may be about the search for extraterrestrial intelligence, would
very likely become bored after many years of unsuccessful searching. A radio
astronomer, like any other scientist, is interested in working on problems that havea high probability of more immediate results.
The ideal strategy would involve a large telescope that could devote something
like half time to the search for extraterrestrial intelligent radio signals and about
half time to the study of more conventional radioastronomical objectives, such asplanets, radio stars, pulsars, interstellar molecules, and quasars. The difficulty inusing several existing radio observatories, each for, say, 1 percent of their time, isthat these activities would have to be pursued for many centuries to have areasonable probability of success. Since the time on existing radio telescopes ismainly spoken for, larger allocations of time seem unlikely.
A wide variety of objects obviously should be examined: G-type stars, like ourown; M-type stars, which are older; and exotic objects, which may be black holesor possible manifestations of astroengineering activities. The number of stars andother objects in our own Milky Way Galaxy is about two hundred billion, and thenumber that we must examine to have a fair chance of detecting such signals
seems to be at least millions.
There is an alternative strategy to searching painfully each of millions of stars
for the signals from a civilization not much more advanced than our own. We
might examine an entire galaxy all at once for signals from civilizations much
more advanced than ours (see Chapters 34 and 35). A small radio telescope canpoint at the nearest spiral galaxy to our own, the great galaxy M31 in theconstellation Andromeda, and simultaneously observe some two hundred billion
stars. Even if many of these stars were broadcasting with a technology only slightly
in advance of our own, we would not pick them up. But if only a few are
broadcasting with the power of a much more advanced civilization, we would
detect them easily. In addition to examining nearby stars only slightly in advanceof us, it therefore makes sense to examine, simultaneously, many stars inneighboring galaxies, only a few of which may have civilizations greatly in advanceof our technology.
We have been describing a search for signals beamed in our general direction
by civilizations interested in communicating with us. We ourselves are notbeaming signals in the direction of some specific other star or stars. If allcivilizations listened and none transmitted, we would each reach the erroneous
conclusion that the Galaxy was unpopulated, except by ourselves. Accordingly, it
has been proposed – as an alternative and much more expensive enterprise – that
we also "eavesdrop"; that is, tune in on the signals that a civilization uses for its
own purposes, such as domestic radio and television transmission, radar
surveillance systems, and the like. A large radio telescope devoting half time to arigorous search for intelligent extraterrestrial signals beamed our way would costtens of millions of dollars (or rubles) to construct and operate. An array of large
radio telescopes, designed to eavesdrop to a distance of some hundreds of lightyears, would cost many billions of dollars.
In addition, the chance of success in eavesdropping may be slight. One hundredyears ago we had no domestic radio and television signals leaking out into space.
One hundred years from now the development of tight beam transmission bysatellites and cable television and new technologies may mean that again no radio
and television signals would be leaking into space. It may be that such signals aredetectable only for a few hundred years in the multibillion-year history of a planet.
The eavesdropping enterprise, in addition to being expensive, may also have a verysmall probability of success.
The situation we find ourselves in is rather curious. There is at least a fair
probability that there are many civilizations beaming signals our way. We have thetechnology to detect these signals out to immense distances – to the other side of
the Galaxy. Except for a few back-burner efforts in the United States and theSoviet Union, we – that is, mankind – are not carrying out the search forextraterrestrial intelligence. Such an enterprise is sufficiently exciting and, at last,
sufficiently respectable that there would be little difficulty in staffing a radio
observatory designed for this purpose with devoted, capable, and innovative

scientists. The only obstacle appears to be money.
While not small change, some tens of millions of dollars (or rubles) is,nevertheless, an amount of money well within the reach of wealthy individuals
and foundations. In fact, there is in astronomy a long and proud history ofobservatories funded by private individuals and foundations: The Lick
Observatory, on Mount Hamilton, California, by Mr. Lick (who wanted to build apyramid, but settled for an observatory – in the base of which he is buried); theYerkes Observatory in Williams Bay, Wisconsin, by Mr. Yerkes; the LowellObservatory in Flagstaff, Arizona, by Mr. Lowell; and the Mount Wilson andMount Palomar Observatories in Southern California, by a foundation establishedby Mr. Carnegie. Government money will probably be forthcoming for such anenterprise eventually. After all, it costs about the same as the replacement costs of 166
U.S. aircraft shot down over Vietnam in Christmas week, 1972. But a radio
telescope designed for communication with extraterrestrial intelligence and an
attached institute of exobiology would make a very fitting personal memorial forsomeone.

Chapter 30: If We Succeed
In considering the problem of interstellar communication, some people areworried. What if a civilization we come into contact with is more advanced thanwe?
The history of contact between advanced and backward technologicalcivilizations on Earth is a sorry one. The technically less advanced societies –
although they may have superior mathematics or astronomy or poetry or moral
precepts – get wiped out. If this is a law of societal natural selection here, why notelsewhere? And in that case, should we not keep quiet?
There are those who predict a dire catastrophe if we broadcast our presence toanother star. The extraterrestrials will come and – eat us, or something equallyunpleasant. (Actually, if we are especially tasty, they need only sample one of us,
determine what sequence of our amino acids makes us appetizing, and thenreconstruct the relevant proteins on their own planet. The high freightage makes
us economically, if not gastronomically, unappetizing.) The message aboard Pioneer
10 was criticized by a few because it "gave away" our position in the Galaxy. I verymuch doubt if we pose any threat to anybody out there. We are the mostbackward possible civilization able to engage in communication, and the vast
spaces between the stars are a kind of natural quarantine, preventing us at any
time in the near future from messing around out there.
But, in any case, it is too late. We have already announced our presence. The
initial radio broadcasts, starting with Marconi and reaching significant intensity inthe 1920s, have leaked through the ionosphere and are expanding at the velocity oflight in a spherical wavefront centered around the Earth. And in that wavefront,
an advanced technical civilization can pick up the tinny transmissions of Enrico
Caruso arias, the Scopes trial, the 1928 election returns, the big jazz bands. These
are the harbingers of the cultures of Earth, our first emissaries to the stars.
If there are technical civilizations some fifty light-years out, they will just now
be detecting these strange, primitive signals. Even if they are poised to respondinstantly with the fastest spaceship possible, it will be at least another fifty years
before we hear from them. Pioneer 10 will take a million years to cover the same
distance.
It is too late to be shy and hesitant. We have announced our presence to thecosmos – in a backward and groping and unrepresentative manner, to be sure –but here we are!

The vast distances between the stars imply that there will be no cosmic
dialogues by radio transmission. Suppose we receive a signal from a civilization atsome likely distance for first contact, such as three hundred light-years. The
message says, perhaps, "Hello, you guys; how are you?" Having long been prepared
for this moment, we immediately reply, let us say, "Fine, how are you?" The totalround-trip communication time would be six hundred years. It's not what you'dcall a snappy conversation.
Six hundred years ago, the Black Death stalked Europe, the Ming dynasty wasjust founded, Charles the Wise sat on the French throne, Gregory XI was Pope,and the Aztecs were hanging those who polluted the water and the air. Six
hundred years is a long time on Earth. Interstellar radio communication will not bea dialogue. It will be a monologue. The dumb guys hear from the smart guys, as if
the astrologer of Charles the Wise were to receive a message from us.
While the time for radio signals to travel a distance of three hundred light-years
is three hundred years, the amount of information that can be conveyed isenormous. In fact, with instrumentation not very much more advanced than ourown, essentially all the important insights of our civilization could be transmitted
in a few days. It would take three hundred years to get there, but only a few days
to be transmitted. But the more lively transmission is in the other direction, fromthe smarts (them) to the dumbs (us) (see Chapter 31). It is possible that there is abreath-taking repository of galactic knowledge being beamed from several
directions at Earth at this moment, advanced text interspersed with primers, so we
can learn Galactic, the language of transmission. But we will not hear it if we do
not listen for it.
But how could we possibly decode such a message? European scholars spent
more than a century in entirely erroneous attempts to decode Egyptian
hieroglyphics before the discovery of the Rosetta Stone and the brilliant attack on
its translation by Young and Champollion. Some ancient languages, such as theglyphs of Easter Island, the writings of the Mayas, and some varieties of Cretan
script, remain completely undecoded to the present time. Yet they were languagesof human beings like ourselves, with common biological instincts and encodings,
and distant from us in time by only a few hundreds to a few thousands of years.
How can we expect that a civilization vastly more advanced than we, and based
entirely upon different biological principles, could ever send a message we could
understand?
The differences in the two cases are intent and intelligence. The objective of
the Easter Island glyphs was not to communicate to twentieth-century scientists. It

was to communicate to other Easter Island inhabitants, or, possibly, to the gods.
The idea of a code, at least in the usual military intelligence application, is to makea message difficult to read. But the situation we are considering is the opposite.
We are considering not cryptography, but anticryptography, the design by a very
intelligent civilization of a message so simple that even civilizations as primitive as
ours can understand it.
The message will be based upon commonalities between the transmitting andreceiving civilizations. Those commonalities are, of course, not any spoken or
written language or any common, instinctual encoding in our genetic materials, butrather what we truly share in common – the universe around us, science andmathematics. There are schemes in which mathematical propositions aretransmitted, conveying such concepts as addition and equality and negation andthen working up to more sophisticated concepts. There are schemes in whichradio messages are sent, which, from the number of constituent bits, are clearly
pictures; when reconstructed as pictures, they can be clearly understood. The
plaque on Pioneer 10 is an example of a sort of picture which, transmitted as an
object on a spacecraft or as a picture by radio transmission, would be reliably
understood by an advanced extraterrestrial civilization. Likewise, similar messages,
coming our way, will be understood by us, if we have the wit to listen.
Some individuals find the absence of a dialogue distressing – as if meaningful
dialogues were commonplace on this planet. Philip Morrison, of the Massachusetts
Institute of Technology, has pointed out that such cultural monologues are
entirely common in the history of mankind; that, for example, the entire cultural
patrimony of classical Greece, which has influenced our civilization in a profoundway, has traveled in only one direction in time. We have not sent our wisdom to
the Greeks. The Greeks have sent their wisdom to us – on paper and parchment,
and not by radio waves, but the principle is the same.
The scientific, logical, cultural, and ethical knowledge to be gained by tuning
into galactic transmissions may be, in the long run, the most profound single eventin the history of our civilization. There will be information in what we will nolonger be able to call the humanities – because our communicants will not behuman. There will be a deparochialization of the way we view the cosmos andourselves. There will be a new perspective on the differences we perceive among
ourselves once we grasp the enormous differences that will exist between us andbeings elsewhere – beings with whom we have nonetheless a serious commonalityof intellectual interest.
But, at the same time, it is not likely to result in discontinuous change. The

information may flutter one day into our radio telescopes at a breathtaking rate of
information transfer. The decoding of the message, the understanding of thecontents, and the extremely cautious application of what we are taught might takedecades or even centuries.
The cultural shock from the content of the message is likely, in the short run,to be small. The main impact will be the receipt of the message itself. Landing ofmen on the Moon is now considered, at least in the United States, as such acommonplace and relatively uninteresting occurrence that I think we can say thereceipt of a message from an extraterrestrial civilization, a message that will take along time to decode and understand, will not be very much more disorienting to
the average man.
Eventually, we may wish to respond.
Why should an advanced society wish to expend the effort to communicate
such information to a backward, emerging, novice civilization like our own? I canimagine that they are motivated by benevolence; that during their emerging
phases, they were themselves helped along by such messages and that this is a
tradition worthy of continuance. There are some science-fiction stories in which
the contents of the message are malevolent, in which we receive instructions forthe construction of a machine, which we then dutifully build and it then dutifully
takes over the Earth. But no one will blindly construct such a machine. No one
will implement the instructions contained in an extraterrestrial message until thefull theoretical underpinnings and scientific bases of the instructions are wellunderstood. This is one reason why the short-term cultural shock of a message will
be small. I do not believe that there is any significant danger from the receipt ofsuch a message, provided the most elementary cautions are adhered to.
It has been suggested that the contents of the initial message received willcontain instructions for avoiding our own self-destruction, a possibly common fateof societies shortly after they reach the technical phase. There are certainly enoughnuclear weapons on our planet today to destroy every man, woman, and childmany times over. It is proposed that advanced extraterrestrial civilizations,motivated either by altruism or through a selfish interest in maintaining astimulating set of communicants, convey the information for stabilizing societies. I
do not know if this is possible; historical differences between organisms andsocieties with billions of years of independent evolution would be enormous. But
it is a possibility not worth ignoring, this feedback hypothesis that the existence ofinterstellar communication enlarges the number of civilizations and may be theagency of our own survival. There is another way in which such a feedback

process works, even if there are no specific instructions on how to avoid
destroying ourselves. There is the matter of time scale. Governments on Earthrarely plan more than five years into the future. Individuals ordinarily makedetailed plans for only much shorter times. Even an unsuccessful search forextraterrestrial intelligence, which may take decades or centuries, is a usefulexample of long-range planning. But think of the consequences of receiving amessage that was transmitted three hundred years ago, and a discussion of which
will take another six hundred years. Awaiting the answer to our reply requires acontinuity of purpose unusual in human institutions. Much of the current
ecological catastrophe is due to a grasp of short-term gains and an awesome
blindness to long-term disasters. The time scale of interstellar civilizations anddiscourse with them provides a sense of historical continuity vital for thecontinuance of our own civilization.

Chapter 31: Cables, Drums, and Seashells
In almost all scientific descriptions of contact between Earth and an
extraterrestrial civilization, the extraterrestrial civilization is described asadvanced.
Why advanced? Why aren't there any primitive civilizations out there,
backward fellows poking around, fumbling over interstellar debris, constantly
botching things up? Why are we obsessed with advanced civilizations?
The answer is very simple: The primitive ones don't talk to us. (The reallysmart ones may not talk to us, either, but that is a point I'll come to in a moment.)
Let us consider contact using radio astronomy. Radio astronomy on Earth is aby-product of the Second World War, when there were strong military pressures
for the development of radar. Serious radio astronomy emerged only in the 1950s,
major radio telescopes only in the 1960s. If we define an advanced civilization as
one able to engage in long-distance radio communication using large radio
telescopes, there has been an advanced civilization on our planet for only about
ten years. Therefore, any civilization ten years less advanced than we cannot talkto us at all.
Even rather optimistic estimates of the rate at which advanced technicalcivilizations emerge in the Galaxy are lower than one every ten years (see Chapter
28). If this is correct, it means that of all the civilizations in the Galaxy able tocommunicate by radio, there is none as dumb as we. There may be millions ofcivilizations less advanced than we, but we have no way to make contact with
them: They lack the technology to receive or transmit. Objections that the Pioneer
10 message may be too difficult for the recipients to decipher ignores the fact thatthe recipients must be able to acquire this tiny bit of space debris in interstellar
space – a task vastly beyond our present capabilities. If they are advanced enoughto capture Pioneer 10 in the dark between the stars, they will, I think, be smart
enough to make out its message, which can be read without special hinting by
many physicists on as backward a planet as Earth (although, to be sure, thosephysicists share some genetic and cultural biases and chauvinisms with the authorsof the message).
But what about civilizations vastly in advance of our own? The amount oftechnical progress we have made in the past few hundred years is startling. Not
only have entire new technologies developed, but entire new laws of physics andentire new ways of examining the universe have evolved. This intellectual andtechnological development is continuing. If Earth's civilization survives, theadvance of science and technology will also continue.
Civilizations hundreds or thousands or millions of years beyond us should havesciences and technologies so far beyond our present capabilities as to beindistinguishable from magic. It is not that what they can do violates the laws ofphysics; it is that we will not understand how they are able to use the laws ofphysics to do what they do.
It is possible that we are so backward and so uninteresting to such civilizations
as not to be worthy of contact, or at least of much contact. There may be a few
specialists in primitive planetary societies who receive master's or doctor's degrees
in studying Earth or listening to our raspy radio and television traffic. There may
be amateurs – Boy Scouts, radio hams, and the equivalent – who may be interested
in developments on Earth. But a civilization a million years in our future isunlikely, I believe, to be very interested in us. There are all those othercivilizations a million years in our future for them to talk to.
Communications between two very advanced civilizations will likely use ascience and a technology inaccessible to us. We therefore have no prospect for
tuning in on such communications traffic, either accidentally or on purpose.
We are like the inhabitants of an isolated valley in New Guinea who
communicate with societies in neighboring valleys (quite different societies, I
might add) by runner and by drum. When asked how a very advanced society willcommunicate, they might guess by an extremely rapid runner or by an improbably
large drum. They might not guess a technology beyond their ken. And yet, all thewhile, a vast international cable and radio traffic passes over them, around them,and through them.
At this very moment the messages from another civilization may be wafting
across space, driven by unimaginably advanced devices, there for us to detect them
– if only we knew how. Perhaps the message will come via radio waves to be
detected by large radio telescopes. Or perhaps by more arcane devices, themodulation of X-ray stars, gravity waves, neutrinos, tachyons, or transmission
channels that no one on Earth will dream of for centuries. Or perhaps themessages are already here, present in some everyday experience that we have notmade the right mental effort to recognize. The power of such an advanced
civilization is very great. Their messages may lie in quite familiar circumstances.
Consider, for example, seashells. Everyone knows the "sound of the sea" to beheard when putting a seashell to one's ear. It is really the greatly amplified soundof our own blood rushing, we are told. But is this really true? Has this beenstudied? Has anyone attempted to decode the message being sounded by theseashell? I do not intend this example as literally true, but rather as an allegory.
Somewhere on Earth there may be the equivalent of the seashell communications
channel. The message from the stars may be here already. But where?
We will listen for the interstellar drums, but we will miss the interstellarcables. We are likely to receive our first messages from the drummers of theneighboring galactic valleys – from civilizations only somewhat in our future. The
civilizations vastly more advanced than we will be, for a long time, remote both in
distance and accessibility. At a future time of vigorous interstellar radio traffic, thevery advanced civilizations may be, for us, still insubstantial legends.

Chapter 32: The Night Freight to the Stars
For three generations of human beings there was – as an ever-present, but almost
unperceived, part of their lives – a sound that beckoned, a call that pierced thenight, carrying the news that there was a way, not so very difficult, to leave Twin
Forks, North Dakota, or Apalachicola, Florida, or Brooklyn, New York. It was thewail of the night freight, as haunting and evocative as the cry of the loon. It was aconstant reminder that there were vehicles, devices, which, if boarded, could
propel you at high velocity out of your little world into a vaster universe of forestsand deserts, seacoasts and cities.
Especially in the United States, but perhaps over much of the world, few
people today travel by train. There are whole generations growing up which havenever heard that siren call. This is the moment of the homogenization of theworld, when the diversities of societies are eroding, when a global civilization is
emerging. There are no exotic places left on Earth to dream about.
And for this reason there remains an even greater and more poignant needtoday for a vehicle, a device, to get us somewhere else. Not all of us; only a few –to the deserts of the Moon, the ancient seacoasts of Mars, the forests of the sky.
There is something comforting in the idea that one day a few representatives of
our little terrestrial village might venture to the great galactic cities.
There are as yet no interstellar trains, no machines to get us to the stars. But
one day they may be here. We will have constructed them or we will haveattracted them.
And then there will once again be the whistle of the night freight. Not theantique sort of whistle, for sound does not carry in interplanetary space or in theemptiness between the stars. But there will be something, perhaps the flash frommagnetobrehmstrahlung, as the starship approaches the velocity of light. There
will be a sign.
Looking out on a clear night from the continent-sized cities and vast gamepreserves that may be our future on this planet, youngsters will dream that when
they are grown, if they are very lucky, they will catch the night freight to the stars.

Chapter 33: Astroengineering
In a by now much quoted and possibly even apocryphal story, the nuclear
physicist Enrico Fermi asked, during a luncheon conversation at Los Alamos in the
middle 1940s, "Where are they?" If there are vast numbers of beings moreadvanced then we, he was musing, why have we seen no sign of them – by avisitation to Earth, for example?
We have discussed this problem in Chapters 27 and 28. But there is anotherformulation of Fermi's question. A civilization a hundred years in our
technological future (assuming present rates of technological growth) would surely
be able to communicate by radio, and possibly by other techniques, anywhere in
the Galaxy and probably with other galaxies as well. A civilization thousands ofyears in our technological future will very likely be able to travel physicallybetween the stars, although with the expenditure of considerable time andresources.
But what of civilizations tens of thousands or hundreds of thousands of years in
our future, or even farther advanced? There are, after all, stars billions of years
older than the Sun. The very oldest such stars lack heavy metals; probably theirplanets are similarly lacking. Such very old stars are inhospitable environments forthe development of technological civilizations. But some stars one or two billion
years older than the Sun have no such attendant difficulties. It is surely possiblethat there are at least a few civilizations hundreds of millions or billions of years in
our technological future.
With prodigious energy resources, such civilizations should be able to rework
the cosmos. We have discussed in Chapter 22 how life on Earth has already altered
our planet significantly and how we can envision in the relatively near future
making important changes in the environments of the nearby planets.
More major changes are possible in the somewhat more distant future. The
mathematician Freeman Dyson, of the Institute for Advanced Study, offers ascheme in which the planet Jupiter is broken down piece by piece, transported tothe distance of the Earth from the Sun, and reconstructed into a spherical shell – aswarm of individual fragments revolving about the Sun. The advantage of Dyson's
proposal is that all of the sunlight now wasted by not falling upon an inhabited
planet could then be gainfully employed; and a population greatly in excess of thatwhich now inhabits the Earth could be maintained. Whether such a vast
population is desirable is an important and unsolved question. But what seems
clear is that at the present rate of technological progress it will be possible toconstruct such a Dyson sphere in perhaps some thousands of years. In that case,other civilizations older than we may have already constructed such sphericalswarms.
A Dyson sphere absorbs visible light from the Sun. But it does not continue
indefinitely to absorb this light without re-radiating; otherwise, the temperature
would become impossibly high. The exterior of the Dyson sphere radiates infrared
radiation into space. Because of the large dimensions of the sphere, the infrared
flux from a Dyson sphere should be detectable over quite sizable distances – withpresent infrared technology, over distances of hundreds to thousands of light-years.
Remarkably enough, large infrared objects of roughly Solar System dimensions andof temperatures less than 1,000 degrees Fahrenheit have been detected in recent
years. These, of course, are not necessarily Dyson civilizations. They may be vast
dust clouds surrounding stars in the process of formation. But we are beginning todetect objects that are not dissimilar to the artifacts of advanced civilizations.
There are many phenomena in contemporary astronomy that are notunderstood. Quasars, for example, are one. The reported very high-intensity
gravitational waves coming from the center of our galaxy are another. The list canbe extended considerably. As long as we do not understand these phenomena, wecannot exclude the possibility that they are manifestations of extraterrestrial
intelligence. This hardly demonstrates the likelihood of extraterrestrial
intelligence, any more than our inability to understand seasonal changes on Mars
(Chapter 19) provided strong evidence for vegetation on that planet. As the Soviet
astrophysicist I. S. Shklovskii says, "Following the principles of law, we should
assume all astronomical phenomena natural until proven otherwise."
Some scientists have asked, in the reformulation of Fermi's question, why it isthat advanced civilizations are not much more obvious. Why have stars not beenrearranged into entirely artificial patterns in the sky – perhaps blinking advertisinglights, detectable over intergalactic distances, for some cosmic soft drink? Thisparticular example is, of course, not very tenable – one society's soft drink may be
another society's poison. More seriously, the manifestations of very advanced
civilizations may not be in the least apparent to a society as backward as we, any
more than an ant performing his anty labors by the side of a suburban swimming
pool has a profound sense of the presence of a superior technical civilization all
around him.

Chapter 34: Twenty Questions: A Classification of Cosmic Civilizations
To deal with the possibility of enormously advanced extraterrestrial civilizations,
the Soviet astrophysicist N. S. Kardashev has proposed a distinction in terms of theenergy available to a civilization for communications purposes.
A Type I civilization is able to muster for communications purposes theequivalent of the entire present power output of the planet Earth – which is now
used for heating, electricity, transportation, and so on; a large variety of purposes
other than communication with extraterrestrial civilizations. By this definition the
Earth is not yet a Type I civilization.
The power usage of our civilization is growing at a rapid rate. The present
power output of planet Earth is something like 1015 or 1016 watts; that is,a million billion to ten million billion watts. The standard exponential notation
simply indicates the number of zeros following the 1. For example, 1015 means fifteen
zeros after the 1. The concept of power in physics is that of an energy expenditure
per unit time. One watt is ten million ergs of energy expended per second. All of
the power used on the Earth is thus equivalent to lighting up, say, one hundred
trillion hundred-watt bulbs. Especially if this energy were put out in the radio partof the spectrum, it might be detected over very sizable distances.
A Type II civilization is able to use for communications purposes a power
output equivalent to that of a typical star, about 1026 watts. We already see
particularly bright stars at optical frequencies in the nearest galaxies. A Type II
civilization, putting out in our direction 1026 watts in some fairly narrow radio
bandpass, could be detectable over vast inter-galactic distances. It would be easily
detectable, if we used the right search procedures, were there only one such
civilization in the nearest spiral galaxy to our own, M31, the great galaxy in theconstellation Andromeda. M31 is by no means the largest galaxy. For example, an
elliptical galaxy, M87 – also known as Virgo A – contains perhaps 10 trillion stars.
Finally, Kardashev imagines a Type III civilization, which would use forcommunications purposes the energy output of an entire galaxy, roughly 1036
watts. A Type III civilization beaming at us could be detected if it were anywherein the universe. There is no provision for a Type IV civilization, which bydefinition talks only to itself. There need not be many Type II or Type III
civilizations for their presence to be felt once a search for extraterrestrial
civilizations is organized in earnest. It may well be that a few Type II or Type III
civilizations would be far more readily detectable than a large number of Type I
civilizations – if they choose to signal us (see Chapter 31).

The energy gap between a Type I and a Type II civilization or between a TypeII and a Type III civilization is enormous – a factor of about ten billion in each
instance. It seems useful, if the matter is to be considered seriously, to have a finer
degree of discrimination. I would suggest Type 1.0 as a civilization using 1016
watts for interstellar communication; Type 1.1, 1017 watts; Type 1.2, 1018
watts, and so on. Our present civilization would be classed as something like Type 0.7.
But there may be more significant ways to characterize civilizations than by theenergy they use for communications purposes. An important criterion of acivilization is the total amount of information that it stores. This information canbe described in terms of bits, the number of yes-no statements concerning itself
and the universe that such a civilization knows.
An example of this concept is the popular game of "Twenty Questions," asplayed on Earth. One player imagines an object or concept and makes an initialclassification of it into animal, vegetable, mineral, or none of these three. To
identify the object or concept, the other players then have a total of twentyquestions, which can only be answered "Yes" or "No." How much information canbe discriminated in this manner?
The initial characterization can be thought of as three yes-no questions:Conceptual or objective? Biological or nonbiological? Plant or animal? If we agree
that a particular game of "Twenty Questions" is in pursuit of something alive, we
have, in effect, answered three questions already by the time the game begins. The
first question divided the universe into two (unequal) pieces. The second question
divided one of those pieces into two more, and the third divided one of thosepieces into yet two more. At this stage we have divided the universe crudely into
2×2×2 = 23 =8 pieces.
When we have finished with our twenty questions, we have "divided the universe into
220 additional (probably unequal) pieces. Now, 2 10 is 1,024. We can perform suchcalculations fairly quickly if we approximate 2 10 by 1,000=103; therefore, 2 20
equals (210)2, which approximately equals (103)2=106. The total number of effective questions,twenty-three, has divided the universe into about 223 , or approximately 107
pieces or bits. Thus, it is possible for skillful players to win at "Twenty Questions" only ifthey live in a civilization that has an information content of about 107 bits.
But, as I discuss below, our civilization is characterized by perhaps 1014 bits.
Therefore, skillful players should win at "Twenty Questions" only about 107 out of1014 times, or one in 107, or one in ten million times. That the game is won more
often in practice is because there is an additional rule – usually unstated but wellunderstood: Namely, that the object or concept being named should be one in thegeneral cultural heritage of all the players. But this must mean that 107 bits canconvey a great deal of information about a civilization, as indeed it can. Philip
Morrison has estimated that the total written contribution to our present civilizationfrom classical Greek civilization is only about 109 bits. Thus, a one-way message,
containing what, by the standards of modern radio astronomy, is a verysmall number of bits, can contain a very significant amount of new informationand can have a powerful influence on a society in the long run.
What is the total number of bits in an English word? In all the books in theworld? There are in general English usage twenty-six letters and a sprinkling ofpunctuation marks. Let us estimate that there are thirty-two such effective"letters." But 32=25; that is, there are something like five bits per letter. If a typical
word has four to six letters (for an average of six letters a word, there would haveto be a lot of fancy words), there will then be about twenty to thirty bits per
word. A typical book – about three hundred words per page and about threehundred pages – would have about a hundred thousand words, or about three
million bits. The largest libraries in the world, such as the British Museum, theBodleian Library at Oxford, the New York Public Library, the Widener Library at
Harvard, and the Lenin Library in Moscow, have no more than about ten million
volumes. This is about 3×1013 bits.
A poor-quality low-resolution photograph may have a million bits in it. A
quite complex caricature or cartoon might have only about a thousand bits. On
the other hand, a large, high-quality color photograph or painting might haveabout a billion bits. Let us make allowances for the amount of fundamental
information contained in graphics, photography, and art in our civilization, as wellas the recorded oral tradition. Let us also try to estimate – this can be done only
very crudely – the information we are born with about how to deal with theworld. (Human beings are, relative to other animals, born with very little suchinformation – we deal with the world much more in terms of learned rather thaninherited or instinctual information.) I estimate, then, that we and our civilization
can be very well characterized by something like 1014 or 1015 bits.
Parenthetically, the ancient Chinese saying that a single picture is worth ten
thousand words (three hundred thousand bits in English; but in Chinese?) isapproximately correct – provided that the picture is not too complex.
We can imagine civilizations that have a much greater number of bits
characterizing their society than characterizes ours. In general, we would expect acivilization high on the energy scale to be high on the information scale. But thisneed not necessarily be true. I certainly can imagine societies that are very
complex and require many more bits to characterize them than our society
requires – but that are not interested in interstellar communication.
Characterization of interstellar civilizations requires us to characterize theirinformation content as well.
If we have used numbers to describe energy, we should perhaps use letters to
describe information. There are twenty-six letters in the English alphabet. If eachcorresponds to a factor of ten in the number of bits, there is the possibility ofcharacterizing with the English alphabet a range of information contents over afactor of 1026 – a very large range, which seems adequate for our purposes. I
propose calling a Type A civilization one at the "Twenty Questions" level,characterized by 106 bits. In practice this is an extremely primitive society – moreprimitive than any human society that we know well – and a good beginningpoint. The amount of information we have acquired from Greek civilization
would characterize that civilization as Type C, although the actual amount of
information that characterized Periclean Athens is probably equivalent to Type Eor so. By these standards, our contemporary civilization, if characterized by 1014
bits of information, corresponds to a Type H civilization.
A combined energy/information characterization of our present global
terrestrial society is Type 0.7H. First contact with an extraterrestrial civilization
would be, I would guess, with a type such as 1.5J or 1.8K. If there were a galactic
civilization of a million worlds, and if each were characterized by a thousand times
the information content of our terrestrial civilization, that galactic civilization
would be of Type Q. A billion such federated galaxies, with all the information
held collectively, would be characterized as a civilization of Type Z.
But as we argue in the next chapter, there is not enough time in the history of
the cosmos for such an intergalactic society to have developed. The run of lettersfrom A to Z appears to run the gamut from societies much more primitive thanany of Man's to societies more advanced than any that could be.

Chapter 35: Galactic Cultural Exchanges
It is possible to speculate on the very distant future of advanced civilizations. We
can imagine such societies in excellent harmony with their environments, their
biology, and the vagaries of their politics, so that they enjoy extraordinarily long
lifetimes. Communications would long have been established with many othersuch civilizations. The diffusion of knowledge, techniques, and points of view
would occur at the velocity of light. In time, the diverse cultures of the Galaxy,
involving a large number of quite different-looking organisms, based on different
biochemistries and different initial cultures, would become homogenized – just as
the diverse cultures of Earth today are in the process of homogenization.
But such cultural homogenization of the Galaxy will take a long time. One
round-trip communication by radio between us and the center of the Milky Way
Galaxy requires sixty thousand years. Cultural homogenization of the Galaxy
would require many such exchanges, even if each exchange involved very large
amounts of information conveyed very efficiently. I find it difficult to believe thatfewer than one hundred exchanges between the remotest parts of the Galaxy
would be adequate for galactic cultural homogenization.
The minimum lifetime for the homogenization of the Galaxy would thus bemany millions of years. The constituent societies must, of course, be stable forcomparable periods of time. Such homogenization need not be desirable, but there
are still strong and obvious pressures for it to occur, as is also the case on the
Earth. If there exists a galactic community of civilizations that truly embraces
much of the Milky Way, and if we are right that no information can betransmitted at a velocity faster than light, then most of the members – and all of
the founding members – of such a community must be at least millions of years
more advanced than we are. For this reason, I think it a great conceit, the idea ofthe present Earth establishing radio contact and becoming a member of a galactic
federation – something like a bluejay or an armadillo applying to the United
Nations for member-nation status.
These velocity-of-light limitations on the speed of communication can also be
applied to the homogenization of the cultures of different galaxies, after ahypothetical period of millions of years in which the stellar civilizations of a given
galaxy achieve a common culture. We can imagine attempts to make contact withsuch galactic federations in other galaxies.
The nearest spiral galaxies are several million light-years away. This means thata single element of the dialogue – a message and its reply – would take periods of

time of several millions to about ten million years. If a hundred such exchanges are
required, the time scale for homogenization of a group of nearby galaxies is then of
the order of a billion years. The galactic societies would have to be stable andpreserve continuity for such periods of time. This would mean that an immensely
old civilization within our Galaxy might have strong learned commonalities withsimilar galactic federations in other members of what astronomers modestly callthe "local" group of galaxies.
These homogenization time scales are beginning to reach a point that strains
credulity. There are sufficient natural catastrophes and statistical fluctuations in
the universe that a stable society – even residing on many different planets
simultaneously for more than a billion years – begins to sound unlikely. Also,
during these immense periods of time the communicating galactic societies willthemselves be evolving; many contacts will be required to maintainhomogenization. The galaxies are so distant one from another that they will always
retain their cultural individuality.
In any case, all bets are off beyond the local group. To have cultural
homogenization with the next such cluster of galaxies like our own, and engage ina hundred message-exchange pairs, would require a time longer than the age of theuniverse. This is not to exclude long individual messages from one galaxy toanother. It may be that enormous amounts of information – about the history of agiven galactic federation, for example – may be well known to civilizations inother galaxies. But there will not be enough time for dialogues. At most, one
exchange would be possible between the most distant galaxies in the universe.
Two exchanges of information at the velocity of light would take more time thanthere is, according to modern cosmology.
We conclude that there cannot be a strongly cohesive network ofcommunicating, unifying intelligences through the whole universe if (1) suchgalactic civilizations evolve upward from individual planetary societies and if (2)the velocity of light is indeed a fixed limit on the speed of informationtransmission, as special relativity requires (i.e., if we ignore such possibilities asusing black holes for fast transport: See Chapter 39). Such a universal intelligenceis a kind of god that cannot exist.
In a way, St. Augustine and many other thoughtful theologians have come torather the same conclusion – God must not live from moment to moment, butduring all times simultaneously. This is, in a way, the same as saying that special
relativity does not apply to Him. But supercivilization gods, perhaps the only ones
that this kind of scientific speculation admits, are fundamentally limited. Theremay be such gods of galaxies, but not of the universe as a whole.

Chapter 36: A Passage to Elsewhen
One of the most pervasive and entrancing ideas of science fiction is time travel. In
The Time Machine, the classic story by H. G. Wells, and in most subsequentrenditions, there is a small machine, constructed usually by a solitary scientist in aremote laboratory. One dials the year of interest, steps into the machine, presses abutton, and presto, here's the past or the future. Among the common devices intime-travel stories are the logical paradoxes that accompany meeting yourself
several years ago; killing a lineal antecedent; interfering directly with a major
historical event of the past few thousand years; or accidentally stepping on a
Precambrian butterfly – you are always changing the entire subsequent history oflife.
Such logical paradoxes do not occur in stories about travel to the future.
Except for the element of nostalgia – the wish we all have to relive or reclaim
some elements of the past – a trip forward in time is surely at least as exciting as
one backward in time. We know rather much about the past and almost nothing
about the future. Travel forward in time has a greater degree of intellectual
excitement than the reverse.
There is no question that time travel into the future is possible: We do it all
the time merely by aging at the usual rate. But there are other, more interesting
possibilities. Everyone has heard about, and now even a fair number of people
understand, Einstein's special theory of relativity. It was Einstein's genius to havesubjected our usual views of space, time, and simultaneity to a penetrating logicalanalysis, which could have been performed two centuries earlier. But special
relativity required for its discovery a mind divested of the conventional prejudicesand the blind adherence to prevailing beliefs – a rare mind in any time.
Some of the consequences of special relativity are counterintuitive, in the sensethat they do not correspond to what everybody knows by observing his
surroundings. For example, the special theory says that a measuring rod shrinks inthe direction in which it is moving. When jogging, you are thinner in the directionin which you are jogging – and not because of any weight loss. The moment youcome to a halt you immediately resume your usual paunch-to-backbone
dimension. Similarly, we are more massive when running than when standing still.
These statements appear silly only because the magnitude of the effect is too small
to be measured at jog velocities. But were we able to jog at some close
approximation to the speed of light (186,000 miles per second), these effects
would become manifest. In fact, expensive synchrotrons – machines to acceleratecharged particles close to the speed of light – take account of such effects, andwork only because special relativity happens to be correct. The reason these
consequences of special relativity seem counterintuitive is that we are not in the
habit of traveling close to the speed of light. It is not that there is anything wrong
with common sense; common sense is fine in its place.
There is a third consequence of special relativity, a bizarre effect important
only close to the speed of light: The phenomenon called time dilation. Were we totravel close to the speed of light, time, as measured by our wristwatch or by ourheartbeat, would pass more slowly than a comparable but stationary clock. Again,
this is not an experience of our everyday life, but it is an experience of nuclear
particles, which have clocks built into them (their decay times) when they travel
close to the speed of light. Time dilation is a measured and authenticated reality of
the universe in which we live.
Time dilation implies the possibility of time travel into the future. A spacevehicle that could travel arbitrarily close to the speed of light arranges for time, as
measured on the space vehicle, to move as slowly as desired. For example, ourGalaxy is some sixty thousand light-years in diameter. At the velocity of light, it
would take sixty thousand years to cross from one end of the Galaxy to the other.
But this time is measured by a stationary observer. A space vehicle able to moveclose to the speed of light could traverse the Galaxy from one end to the other inless than a human lifetime. With the appropriate vehicle we could circumnavigate
the Galaxy and return almost two hundred thousand years later, as measured on
Earth. Naturally, our friends and relatives would have changed some in the interval– as would our society and probably even our planet.
According to special relativity, it is even possible to circumnavigate the entire
universe within a human lifetime, returning to our planet many billions of years in
our future. According to special relativity, there is no prospect of traveling at the
speed of light, merely very close to it. And there is no possibility in this way oftraveling backward in time; we can merely make time slow down, we cannot
make it stop or reverse.
The engineering problems involved in the design of space vehicles capable ofsuch velocities are immense. Pioneer 10, the fastest man-made object ever to leave
the Solar System, is traveling about ten thousand times slower than the speed oflight. Time travel into the future is thus not an immediate prospect, but it is a
prospect conceivable for an advanced technology on planets of other stars.
There is one further possibility that should be mentioned; it is a much more
speculative prospect. At the end of their lifetimes, stars more than about 2.5 times
as massive as our Sun undergo a collapse so powerful that no known forces canstop it. The stars develop a pucker in the fabric of space – a "black hole" – into
which they disappear. The physics of black holes does not involve Einstein's
special theory of relativity; it involves his much more difficult general theory of
relativity. The physics of black holes – particularly, rotating black holes – is rather
poorly understood at the present time. There is, however, one conjecture that has
been made, which cannot be disproved and which is worthy of note: Black holes
may be apertures to elsewhen. Were we to plunge down a black hole, we would
re-emerge, it is conjectured, in a different part of the universe and in anotherepoch in time. We do not know whether it is possible to get to this other place inthe universe faster down a black hole than by the more usual route. We do notknow whether it is possible to travel into the past by plunging down a black hole.
The paradoxes that this latter possibility imply could be used to argue against it,
but we really do not know.
For all we do know, black holes are the transportation conduits of advanced
technological civilizations – conceivably, conduits in time as well as in space. A
large number of stars are more than 2.5 times as massive as the Sun; as far as we
can tell, they must all become black holes during their relatively rapid evolution.
Black holes may be entrances to Wonderlands. But are there Alices or whiterabbits?

Chapter 37: Starfolk
I. A Fable
Once upon a time, about ten or fifteen billion years ago, the universe waswithout form. There were no galaxies. There were no stars. There were noplanets. And there was no life. Darkness was upon the face of the deep. The
universe was hydrogen and helium. The explosion of the Big Bang had passed, andthe fires of that titanic event – either the creation of the universe or the ashes of aprevious incarnation of the universe – were rumbling feebly down the corridors ofspace.
But the gas of hydrogen and helium was not smoothly distributed. Here andthere in the great dark, by accident, somewhat more than the ordinary amount ofgas was collected. Such clumps grew imperceptibly at the expense of theirsurroundings, gravitationally attracting larger and larger amounts of neighboringgas. As such clumps grew in mass, their denser parts, governed by the inexorable
laws of gravitation and conservation of angular momentum, contracted andcompacted, spinning faster and faster. Within these great rotating balls andpinwheels of gas, smaller fragments of greater density condensed out; theseshattered into billions of smaller shrinking gas balls.
Compaction led to violent collisions of the atoms at the centers of the gas balls.
The temperatures became so great that electrons were stripped from protons in
the constituent hydrogen atoms. Because protons have like positive charges, they
ordinarily electrically repel one another. But after a while the temperatures at thecenters of the gas balls became so great that the protons collided withextraordinary energy – an energy so great that the barrier of electrical repulsionthat surrounds the proton was penetrated. Once penetration occurred, nuclear
forces – the forces that hold the nuclei of atoms together – came into play. Fromthe simple hydrogen gas the next atom in complexity, helium, was formed. In thesynthesis of one helium atom from four hydrogen atoms there is a small amount ofexcess energy left over. This energy, trickling out through the gas ball, reached thesurface and was radiated into space. The gas ball had turned on. The first star wasformed. There was light on the face of the heavens.
The stars evolved over billions of years, slowly turning hydrogen into helium intheir deep interiors, converting the slight mass difference into energy, and flooding
the skies with light. There were in these times no planets to receive the light, andno life forms to admire the radiance of the heavens.

The conversion of hydrogen into helium could not continue indefinitely.
Eventually, in the hot interiors of the stars, where the temperatures were highenough to overcome the forces of electrical repulsion, all the hydrogen was
consumed. The fires of the stars were stoked. The pressures in the interiors could
no longer support the immense weight of the overlying layers of star. The stars
then continued their process of collapse, which had been interrupted by the
nuclear fires of a billion years before.
In contracting further, higher temperatures were reached, temperatures so highthat helium atoms – the ash of the previous epoch of nuclear reaction – became
usable as stellar fuel. More complex nuclear reactions occurred in the insides ofthe stars – now swollen, distended red giant stars. Helium was converted tocarbon, carbon to oxygen and magnesium, oxygen to neon, magnesium to silicon,
silicon to sulfur, and upward through the litany of the periodic table of theelements – a massive stellar alchemy. Vast and intricate mazes of nuclear reactions
built up some nuclei. Others coalesced to form much more complex nuclei. Stillothers fragmented or combined with protons to build only slightly more complex
nuclei.
But the gravity on the surfaces of red giants is low, because the surfaces have
expanded outward from the interiors. The outer layers of red giants are slowly
dissipated into interstellar space, enriching the space between the stars in carbon
and oxygen and magnesium and iron and all the elements heavier than hydrogenand helium. In some cases, the outer layers of the star were slowly stripped off,
like the successive skins of an onion. In other cases, a colossal nuclear explosion
rocked the star, propelling at immense velocity into interstellar space most of theoutside of the star. Either by leakage or explosion, by dissipation slow ordissipation fast, star-stuff was spewed back to the dark, thin gas from which thestars had come.
But here, later generations of stars were aborning. Again the condensations ofgas spun their slow gravitational pirouettes, slowly transmogrifying gas cloud intostar. But these new second- and third-generation stars were enriched in heavy
elements, the patrimony of their stellar antecedents. Now, as stars were formed,
smaller condensations formed near them, condensations far too small to produce
nuclear fires and become stars. They were little dense, cold clots of matter, slowly
forming out of the rotating cloud, later to be illuminated by the nuclear fires thatthey themselves could not generate. These unprepossessing clots became theplanets: Some giant and gaseous, composed mostly of hydrogen and helium, coldand far from their parent star; others, smaller and warmer, losing the bulk of theirhydrogen and helium by a slow trickling away to space, formed a different sort ofplanet – rocky, metallic, hard-surfaced.
These smaller cosmic debris, congealing and warming, released small quantities
of hydrogen-rich gases, trapped in their interiors during the processes of formation.
Some gases condensed on the surface, forming the first oceans; other gases
remained above the surface, forming the first atmospheres – atmospheres different
from the present atmosphere of Earth, atmospheres composed of methane,ammonia, hydrogen sulfide, water, and hydrogen – an unpleasant and unbreathable atmosphere for humans. But this is not yet a story about humans.
Starlight fell on this atmosphere. Storms were driven by the Sun, producing
thunder and lightning. Volcanoes erupted, hot lava heating the atmosphere near
the surface. These processes broke apart molecules of the primitive atmosphere.
But the fragments reassorted into more and more complex molecules, falling into
the early oceans, there interacting with each other, falling by chance upon clays, adizzying process of breakdown, resynthesis, transformation – slowly moving
toward molecules of greater and greater complexity, driven by the laws of physics
and chemistry. After a time, the oceans achieved the constituency of a warm
dilute broth.
Among the innumerable species of complex organic molecules forming anddissipating in this broth there one day arose a molecule able crudely to makecopies of itself – a molecule which weakly guided the chemical processes in its
vicinity to produce molecules like itself – a template molecule, a blueprint
molecule, a self-replicating molecule. This molecule was not very efficient. Its
copies were inexact. But soon it gained a significant advantage over the othermolecules in the early waters. The molecules that could not copy themselves did
not. Those that could, did. The number of copying molecules greatly increased.
As time passed, the copying process became more exact. Other molecules in
the waters were reprocessed to form the jigsaw puzzle pieces to fit the copying
molecules. A minute and imperceptible statistical advantage of the molecules that
could copy themselves was soon transformed by the arithmetic of geometricalprogression into the dominant process in the oceans.
More and more elaborate reproductive systems arose. Those systems that
copied better produced more copies. Those that copied poorly produced fewer
copies. Soon most of the molecules were organized into molecular collectives, into
self-replicating systems. It was not that any molecules had the glimmering of an
idea or the ghostly passage of a need or want or aspiration; merely, thosemolecules that copied did, and soon the face of the planet became transformed by
the copying process. In time, the seas became full of these molecular collectives,
forming, metabolizing, replicating … forming, metabolizing, replicating …

forming, metabolizing, mutating, replicating… Elaborate systems arose, molecularcollectives exhibiting behavior, moving to where the replication building blocks
were more abundant, avoiding molecular collectives that incorporated theirneighbors. Natural selection became a molecular sieve, selecting out thosecombinations of molecules best suited by chance to further replication.
All the while the building blocks, the foodstuffs, the parts for later copies,
were being produced, mainly by sunlight and lightning and thunder – all driven by
the nearby star. The nuclear processes in the insides of the stars drove theplanetary processes, which led to and sustained life.
As the supply of foodstuffs gradually was exhausted, a new kind of molecularcollective arose, one able to produce molecular building blocks internally out of
air and water and sunlight. The first animals were joined by the first plants. The
animals became parasites upon the plants, as they had been earlier on the stellar
manna falling from the skies. The plants slowly changed the composition of theatmosphere; hydrogen was lost to space, ammonia transformed to nitrogen, 196
methane to carbon dioxide. For the first time, oxygen was produced in significant
quantities in the atmosphere – oxygen, a deadly poisonous gas able to convert all
the self-replicating organic molecules back into simple gases like carbon dioxide
and water.
But life met this supreme challenge: In some cases by burrowing into
environments where oxygen was absent, but – in the most successful variants – byevolving not only to survive the oxygen but to use it in the more efficientmetabolism of foodstuffs.
Sex and death evolved – processes that vastly increased the rate of natural
selection. Some organisms evolved hard parts, climbed onto, and survived on theland. The pace of production of more complex forms accelerated. Flight evolved.
Enormous four-legged beasts thundered across the steaming jungles. Small beasts
emerged, born live, instead of in hard-shelled containers filled with replicas of theearly oceans. They survived through swiftness and cunning – and increasingly long
periods in which their knowledge was not so much preprogrammed in selfreplicating molecules as learned from parents and experiences.
All the while, the climate was variable. Slight variations in the output ofsunlight, the orbital motion of the planet, clouds, oceans, and polar icecaps
produced climatic changes – wiping out whole groups of organisms and causing
the exuberant proliferation of other, once insignificant, groups.
And then … the Earth grew somewhat cold. The forests retreated. Smallarboreal animals climbed down from the trees to seek a livelihood on the savannas.
They became upright and tool-using. They communicated by producing
compressional waves in the air with their eating and breathing organs. They
discovered that organic material would, at a high enough temperature, combinewith atmospheric oxygen to produce the stable hot plasma called fire. Postpartum
learning was greatly accelerated by social interaction. Communal hunting
developed, writing was invented, political structures evolved, superstition andscience, religion and technology.
And then one day there came to be a creature whose genetic material was inno major way different from the self-replicating molecular collectives of any of theother organisms on his planet, which he called Earth. But he was able to ponder
the mystery of his origins, the strange and tortuous path by which he had emerged
from star-stuff. He was the matter of the cosmos, contemplating itself. He
considered the problematical and enigmatic question of his future. He called
himself Man. He was one of the starfolk. And he longed to return to the stars.

Chapter 38: Starfolk
II. A Future
The story of the preceding chapter is a kind of scientific fable. It is more or lesswhat many modern scientists believe on the basis of available evidence. It is theoutline of the emergence of man, a process wending through billions of years oftime and driven by gravitation and nuclear physics, by organic chemistry andnatural selection. It tells how the matter of which we are made was generated inanother place and another time, in the insides of a dying star five billion or more
years ago.
There are three aspects of the fable that I find particularly interesting. First,
that the universe is put together in such a way as to permit, if not guarantee, theorigin of life and the development of complex creatures. It is easy to imagine lawsof physics that would not permit appropriate nuclear reactions, or laws ofchemistry that would not permit appropriate configurations of molecules to beassembled. But we do not live in such universes. We live in a universe remarkably
hospitable to life.
Second, there is in the fable no step unique to our Solar System or to ourplanet. There are 250 billion suns in our Milky Way Galaxy, and billions of othergalaxies in the heavens. Perhaps half of these stars have planets at biologicallyappropriate distances from the local sun. The initial chemical constituents for theorigin of life are the most abundant molecules in the universe. Something like theprocesses that on Earth led to man must have happened billions of other times in
the history of our Galaxy. There must be other starfolk.
The evolutionary details would not be the same, of course. Even if the Earthwere started over again and only random forces again operated, nothing like ahuman being would be produced – because human beings are the end product ofan exquisitely complicated evolutionary pathway full of false starts and dead ends
and statistical accidents. But we might well expect, if not human beings, organisms
functionally not very different from ourselves. Since there are second- and thirdgeneration stars much older than our Sun, there must be, I think, many places in
the Galaxy where there are beings far more advanced than we in science andtechnology, in politics, ethics, poetry, and music.
The third point is the most arresting. It is the intimate connection between
stars and life. Our planet was formed from the dregs of star-stuff. The atoms
necessary for the origin of life were cooked in the interiors of red giant stars. Theseatoms were forced together, to form complex organic molecules, by ultraviolet
light and thunder and lightning, all produced by the radiation of our neighboring
Sun. When the food supply ran short, green-plant photosynthesis developed,
driven again by sunlight, the sunlight off which almost all the organisms on Earth,and certainly everyone we know, live out their days.
But this cannot be the end of the fable. Our Sun is only approaching vigorous
middle age. It has perhaps another five billion or ten billion years of stellar life
ahead of it.
And what of life on Earth and man? They, too, for all we know, may have afuture. And if not, there are billions of other stars and probably billions of otherinhabited planets in our Galaxy. What is the interaction between stars and life
later on?
The death of stars is taking astronomers into unexpected and almost surreal
celestial landscapes. One of these is the supernova explosion, the death throes of astar slightly more massive than our Sun. In a brief period of a few weeks to a few
months, such an exploding star may become brighter than the rest of the galaxy inwhich it resides. In super-novae, elements like gold and uranium are generated
from iron. The supernovae are the long-sought Philosopher's Stone, convertingbase metals into precious metals.
Having blown away most of its star-stuff – destined, some of it, to go into later
generations of formation of stars and planets and life – the star settles down to aquiet old age, its fires spent, as a white dwarf. A white dwarf is constituted ofmatter in a state that physicists, with no moral imputation intended, calldegenerate. Electrons are stripped off the nuclei of atoms. The protective shieldsof negative electricity are removed. The nuclei can move much closer together,and a state of extraordinary density results. Typical degenerate matter weighs
about a ton per thimbleful. Some white dwarfs, properly considered, are vast
stellar crystals able to hold up the weight of the overlying layers of the star. Some
white dwarfs are largely carbon. We may speak of a star made of diamond.
But for more massive stars, the white dwarfs – their embers slowly fading,decaying into black dwarfs – are not the end state. Degenerate matter cannot holdup the weight of a more massive star, and another cycle of stellar contraction thus
ensues – the matter being crushed together to more and more incredible densities,
until some new regime of physics is entered, until some new force surfaces to stop
the stellar collapse. There is only one further such force known: It is the nuclear
force that holds the nucleus of the atom together. This nuclear force is responsible
for the stability of atoms and, therefore, for all of chemistry and biology. It is also

responsible for the thermonuclear reactions in the insides of stars that make stars
shine and, thereby, in a quite different way, drives planetary biology.
Imagine a star more or less like the Sun, but a little more massive, near the endof its days of converting simple nuclei into more complex nuclei. It produces thelast series of complex nuclear reactions it is able to – and then collapses. As its size
decreases, it spins more and more rapidly, like a pirouetting ice skater bringing in
her arms. Only when the density in its interior becomes comparable to the densityof matter inside the atomic nucleus does the collapse stop. It is a simple matter inelementary physics to calculate at what stage the collapse will end. It ends when
the star is about a mile across and rotating about ten times a second.
Such an object is a rapidly rotating neutron star. It is, in truth, a giant atomic
nucleus a mile across. Neutron star matter is so dense that a speck of it – justbarely visible – would weigh a million tons. The Earth would not be able tosupport it. A piece of neutron star matter, if it could be transported to the Earthwithout falling apart, would sink effortlessly through the crust, mantle, and core of
our planet like a razor blade through warm butter.
Such neutron stars were theoretical constructs, the imaginings of speculative
physicists – until the pulsars were discovered. Pulsars are sources of radio emission.
Some of them are associated with old supernova explosions. They blink at us as if
the beam of some cosmic lighthouse swept by us ten times a second. The detailsof the emission from pulsars are best understood if they are the fabled neutronstars. Because of the loss of energy to space that we observe, the rotation rate of an
isolated neutron star must slowly decline, even though it is a stellar timekeeper ofextraordinary accuracy. The observed decay of pulsar periods is just about what is
expected from neutron star physics.
The first pulsar to be detected was called, by its discoverers, only half impishly,
LGM-1. The LGM stood for "little green men." Was it, they wondered, a beaconfrom an advanced extraterrestrial civilization? My own view, when I first heard
about pulsars, was that they were perfect interstellar navigation beacons, the sorts
of markers that an interstellar spacefaring society would want to place throughout
the Galaxy for time- and space-fixes for their voyages. There is now little doubtthat pulsars are neutron stars. But I would not exclude the possibility that if there
are interstellar space-faring societies, the naturally formed pulsars are used as
navigation beacons and for communications purposes.
The state of matter in the inside of such a neutron star is still not understood.
We do not know if a surface crust comprising a neutron crystal lattice overlies acore of liquid neutrons. Should the core be solid, starquakes are expected – ashifting of the matter under enormous stress in the interior of the star. Suchstarquakes should produce a discontinuous change in the period of rotation of theneutron star. Such changes, called "glitches," are observed.
Some were disappointed to learn that pulsars were neutron stars and notinterstellar radio communication channels. But pulsars are hardly uninteresting.
Indeed, a star more massive than the Sun that fits into a sphere a mile across androtates ten times every second is, in a certain sense, much more exotic than acivilization slightly more advanced than we, on the planet of another star.
But there is another and much more profound way in which neutron stars andsupernova explosions are connected with life. In a supernova explosion, as wehave already mentioned, vast quantities of atoms from the surface of the star areejected at very high velocities into interstellar space. In the case of the neutronstar, there is, because of its rapid rotation, a zone, not far from its surface, which isrotating at almost the speed of light. Particles are ejected from that zone at
velocities so great that the theory of relativity must be taken into account todescribe them. Both supernova explosions and the high-velocity zone surrounding 201
neutron stars must produce cosmic rays – the very fast charged particles (mostly
protons, but containing all the other elements as well) that pervade the space
between the stars.
Cosmic rays fall on the Earth's atmosphere. The less energetic particles areabsorbed by the atmosphere or deflected by Earth's magnetic field. But the moreenergetic particles, the ones produced by supernovae or neutron stars, penetrate to
the surface of the Earth. And here they collide with life. Some cosmic rays
penetrate through the genetic material of life forms on the surface of our planet.
These random, unpredictable cosmic rays produce changes, mutations, in thehereditary material. Mutations are variations in the blueprints, the hereditary
instructions, contained in our self-replicating molecules. Like a fine watch
repeatedly hit with a hammer, the functioning of life is unlikely to improve undersuch random pummelings. But as sometimes happens with watches or bulky
television sets, a random pummeling does occasionally improve the functioning.
The vast bulk of mutations are harmful, but the small fraction of mutations thatare an improvement provide the raw material for evolutionary advance. Life
would be at a dead end without mutation. Thus, in yet another way, life on Earthis intimately bound to stellar events. Human beings are here because of theparoxysms in dying stars thousands of light-years away.
The births of stars generate the planetary nurseries of life. The lives of stars
provide the energy upon which life depends. The deaths of stars produce theimplements for the continued development of life in other parts of the Galaxy. Ifthere are on the planets of dying stars intelligent beings unable to escape their fate,they may at least derive some comfort from the thought that the death of theirstar, the event that will cause their own extinction, will, nevertheless, provide themeans for continued biological advance of the starfolk on a million other worlds.

Chapter 39: Starfolk
III. The Cosmic Cheshire CatsThe neutron star is not the most exotic inhabitant of the stellar bestiary. A starlarger than three times the mass of our Sun is too big even for nuclear forces tostop its collapse. Once the collapse begins, there is nothing to stop it. The star
contracts to one mile across and continues to shrink. The density passes that of thenucleus of an atom, and matter is further crushed together. The gravitational fieldin the vicinity of such a massive dying star continues to increase. Eventually, thegravity is so strong that not only is matter unable to leave the star, but light is also
trapped. A photon traveling at the speed of light away from the star is constrained
to follow a curved path and fall back upon the star, just as the Earth's gravity is
too strong for any of us to throw a rock to escape velocity. Such stars are too
massive for even photons to escape. Consequently, they are dark. They cannot beseen directly, because no light emanates from them. They are present
gravitationally, but not optically. They are called "black holes." They are beasts
akin to the smile on the Cheshire cat. They are enormous stars that have winked
out but are still there.
Black holes are basically theoretical concepts. They may sound no more likely
than, and not nearly as charming as, the elves of Middle Earth. But they areprobably there. In fact, much of the mass of the Galaxy may reside not in stars we
can see, nor in the gas and dust between the stars, but in black holes peppering the
Galaxy like the holes in an Emmenthaler cheese.
The first black hole may have been found. Cygnus X-1 is a rapidly varying
source of X-rays, visible light, and radio waves. Its X-ray emission was monitoredfrom NASA's UHURU satellite, launched from an Italian launch complex off thecoast of Kenya. All the clues point to Cyg X-1's being a binary star, two stars
revolving around each other in a regular and intricate waltz. From the motion of
the one star we see, we can deduce the mass of the star we cannot. It turns out tobe a massive star, perhaps ten times the mass of our Sun. Such a massive starshould ordinarily be very bright. Yet there is no optical hint of its presence. The
bright star in Cyg X-1 is revolving about a massive object that is present
gravitationally but not optically. It is very likely a black hole a few thousand lightyears from Earth.
Black holes may have their uses. What we know about them till now is entirely
theoretical, not tested against the skeptical standards of observation. There aresome strange possibilities that have been suggested for black holes. Since there isno way to get out of a black hole, it is, in a sense, a separate universe.
In fact, our own universe is very likely itself a vast black hole. We have noknowledge of what lies outside our universe. This is true by definition, but also
because of the properties of black holes. Objects that reside in them cannot
ordinarily leave them. In a strange sense, our universe may be filled with objects
that are not here. They are not separate universes. They do not have the mass of
our universe. But in their separateness and their isolation they are autonomous
universes.
There is an even more bizarre prospect. In one speculative view (Chapter 36),
an object that plunges down a rotating black hole may re-emerge elsewhere andelsewhen – in another place and another time. Black holes may be apertures to
distant galaxies and to remote epochs. They may be shortcuts through space andtime. If such holes in the fabric of the space-time continuum exist, it is by nomeans certain that it would ever be possible for an extended object like aspacecraft to use a black hole for travel through space or time. The most serious
obstacle would be the tidal force exerted by the black hole during approach – aforce that would tend to pull any extended matter to pieces. And yet it seems tome that a very advanced civilization might cope with the tidal stresses of a blackhole.
How many black holes are there in the sky? No one knows at present, but an
estimate of one black hole for every hundred stars seems modest by at least sometheoretical estimates. I can imagine, although it is the sheerest speculation, afederation of societies in the Galaxy that have established a black hole rapidtransit system. A vehicle is rapidly routed through an interlaced network of black
holes to the black hole nearest its destination.
At a typical place in the Galaxy, one hundred stars are encompassed within avolume of radius of about twenty light-years. If we imagine relativistic spacevehicles for the short journeys – the local trains or shuttles – it would take only a
few years' ship time to get from the black hole to the farthest star of the hundred.
One year on board the relativistic shuttle would be occupied accelerating at about
1 g, the acceleration we are familiar with because of the gravity of Earth. After one
year at 1 g, we would approach the speed of light. Another year would be spent
doing a similar deceleration at 1 g at the end-point of the journey. A galaxy withsuch a transportation system, a million separately arisen civilizations and large
numbers of worlds with colonies, exploratory parties, and work teams – a galaxy
where the individuality of the constituent cultures is preserved but a common
galactic heritage established and maintained; a galaxy in which the long travel

times make trivial contact difficult, and the black hole network makes important
contact possible – that would be a galaxy of surpassing interest.
I can imagine, in such a galaxy, great civilizations growing up near the black
holes, with the planets far from black holes designated as farm worlds, ecologicalpreserves, vacations and resorts, specialty manufacturers, outposts for poets andmusicians, and retreats for those who do not cherish big-city life. The discovery ofsuch a galactic culture might happen at any moment – for example, by radio
signals sent to the Earth from civilizations on planets of other stars. Or such a
discovery might not occur for many centuries, until a lone small vehicle from
Earth approaches a nearby black hole and there discovers the usual array of buoys
to warn off improperly outfitted spacecraft, and encounters the local immigration
officers, among whose duties it is to explain the transportation conventions to
newly arrived yokels from emerging civilizations.
The deaths of massive stars may provide the means for transcending thepresent boundaries of space and time, making all of the universe accessible to life,and – in the last deep sense – unifying the cosmos.

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