Roadmap

for the

Office of

Space Science

Origins

Theme

2003

ORIGINS
“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.

Through the unknown, remembered gate

When the last of earth left to discover

Is that which was the beginning...”

T. S. ELIOT

FOUR QUARTETS
ORIG

T

About 

Emergence of the Mo

...to understand how today’s universe of 

p

Star

...to learn how stars and 

Habitable Pl

...to explore the diversity of other worlds an

that 

Origins Missi

...to build on the past, and leave a legacy fo

Enabling 

...to invent the tools for a new 

Research 

...to develop new experiment concepts, an

test theo

Engag

...to share, to inspire, to educate all American

of disco

Scie
II

ORIGINS
NASA’S MISSION

To understand and protect our home planet

To explore the universe and search for life

To inspire the next generation of explorers

...as only NASA can

NASA’S VISION

To improve life here,

To extend life to there,

To find life beyond
IV

ORIGINS
The universe is enormous and

ancient, but life—tiny and

transient—is its precious jewel.
Emergence of the Modern Univ

C
1

In the 20th century we learned that our Milky Way

Galaxy—a massive pinwheel of stars and gas bound

by gravity—has been home to many generations

of stars. Most of these billions of stars are likely to

have “solar systems” of planets like our own—might

they be home to billions of planets like Earth where

life abounds? Only in the last few decades have

we come to realize how closely bound our own

existence is to the birth and death of these stars.

Theoretical models of the Big Bang—the violent

event that began the universe—describe an infant

universe devoid of heavy elements such as carbon,

nitrogen, oxygen, and iron that are essential ingredients of planet Earth and life itself. Where, then,

did these essential heavy elements come from? It

took decades of scientific research to discover how

our Sun, along with every other “sun” that makes

up our galaxy, manufactures heavy elements in the

course of the nuclear fusion which powers it. In its

death throes a star gently releases, or violently hurls,

much of this material into space, where it can later

collect to give rise to new stars further enriched

with the building blocks of planets and life. This

is the galactic ecosystem.

There is growing evidence that star formation

began before there were galaxies, and that when

these early stars died explosively as supernovae they

produced the first spray of heavy elements. But it

also appears that the birth of galaxies, by binding

the stars and gas together to create these cosmic

ecosystems, was crucial to the buildup of heavy

elements to a level where planets and life were possible. The emergence of such enormous structures

from the near-featureless universe that preceded

them, and the manufacture of vast amounts of

heavy elements by their stars, were key steps on

the road to life.

The modern era of the universe began, then,

with the birth of stars and galaxies. Even as we

work to trace the origins of the universe all the way

back to the Big Bang, we recognize that our origins

sensibly began later, some hundreds of millions of

years after the Big Bang. In the billions of years

since, complex chemistry and biology have evolved

from the simple beginnings of the first stars and

the first galaxies. Remarkably, astronomers can

travel back through time to witness these crucial

steps in our origins.

Our research will focus on two areas:

• How did the cosmic web of matter organize into

the first stars and galaxies?

• How do different galactic ecosystems (of stars

and gas) form and which can lead to planets and

living organisms?

O B J E C T I V E O N E

Stars began to form even before the first galaxies, and what had been a calm, near-formless sea began

to surge with the froth of complex forms of matter and energetic processes. Today the universe is full of

structure, from the giant but simple galaxy to a minuscule but complex single living cell. Our objective is to

understand how this came about, how stars and planets form, how the chemical elements are made, and

ultimately how life originates.

...to understand how today’s universe of galaxies,

stars, and planets came to be.

1
2

In an effort to serve students

with special needs, a scientist

and a Braille book author have

used funding from the Hubble

Space Telescope (HST) Cycle

Education and Public Outreach

(E/PO) grant program to

develop Touch the Universe: A

NASA Braille Book of Astronomy.

Dr. Bernhard Beck-Winchatz, an

astronomer at DePaul University in Chicago, wanted visually

impaired students to experience the excitement generated

by HST’s beautiful images of

the universe. When Dr. BeckWinchatz received an HST

research grant, he took advantage of the opportunity to

apply for a supplemental educational grant to work with

noted Braille book author

Noreen Grice in creating a

book of HST images accessible

to visually impaired students.

Touch the Universe contains

14 spectacular HST images,

each printed in color and

supplemented by a transparent

tactile overlay in which the

color features are represented

by tactile symbols. Through

these images, the reader is

taken on a journey of discovery

to more and more distant

objects, starting with images

of the telescope itself in orbit

and ending with the HST Deep

Field image of some of the most

distant galaxies in the universe.

Accompanying explanatory text

is given in both Braille and large

print so that readers of all visual

abilities are able to view and

Touch the Universe: A NASA Braille Book of Astronomy

2

read the book together. With

plans for large-scale publication and distribution under

way, the success of Touch the

Universe indicates how a relatively small amount of money

can result in a national product.

O B J E C T I V E O N E
3

How did the cosmic web of matter organize into

the first stars and galaxies?

Research Area One

Today’s universe is full of structure—galaxies, stars,

planets, and life. However, we now know that immediately after the Big Bang the distribution of matter

and energy in the universe was almost perfectly

smooth. Experiments such as BOOMERANG,

COBE, and MAXIMA have measured very small

irregularities—a thousandth of one percent—in the

brightness of the cosmic microwave background, the

vast sea of primordial radiation that shows us the

universe at an age of a few hundred thousand years.

Under the influence of gravity, the tiny fluctuations

gradually built a weblike structure of mostly hydrogen gas and “dark matter” (whose nature remains

mysterious) within which stars and galaxies would

later form. A key program for the Origins theme is

to provide a detailed account of how this happened.

Modern computer simulations suggest that the

growth of structure advanced through the hierarchical mergers of dark matter concentrations—

“halos,” as they are called. Eventually the gravity of

the largest halos grew strong enough to pull in and

concentrate the gas needed to build an infant galaxy.

However, the first generation of stars may actually

have preceded galaxies. With no heavy elements the

cooling of the gas would have been very inefficient.

Theorists have suggested that such different conditions would have led to a generation of short-lived

stars, considerably more massive, hotter, and brighter

than those we observe around us today. With their

violent supernova deaths these first stars would have

rapidly “polluted” the gas with heavy elements,

thereby dramatically changing the climate for future

star formation. The remnant black holes these

supernovae likely left behind may have seeded the

growth of supermassive black holes that powered

the first quasars.

The energy in starlight comes from nuclear fusion

reactions in the stellar core. However, a comparable

amount of light comes from the release of gravitational potential energy as matter falls (“accretes”)

into super-massive black holes at the centers of large

galaxies. A quasar—the extreme manifestation of this

process—can for a time outshine all the stars in its

galaxy. The release of highly energetic photons from

these first stars and quasars heated the gas and ionized it. We seek to understand how this happened,

in detail, and how it affected the formation of later

generations of stars and black holes. Ultimately, we

want to know how all the relevant processes worked

together to integrate gas, stars, and black holes into

the dark matter halos to form the first galaxies. This

means tracing the growth of dark matter halos, the

distribution of gas in space and time, the synthesis

of the heavy elements, and the buildup of stars and

their remnants as the universe ages. A particularly

important epoch lies between redshifts of 1 and 3

(from about 7 to 10 billion years ago), when the

present-day universe began to take shape.

These questions lead us to pursue three investigations in this area:

• Study how pristine gas from the Big Bang condensed into the first generation of stars, and how

their supernovae produced the first heavy

chemical elements.

• Observe the enormous release of energy during

the building of the first massive black holes that

combined with energy from the first stars to

change the structure of the early universe.

• Describe the assembly of galaxies and their subsequent evolution from generations of stars, leading

to the diversity of galaxies in today’s universe.

O B J E C T I V E O N E
4

INVESTIGATION 1

Study how pristine gas from the Big Bang condensed

into the first generation of stars, and how their supernovae produced the first heavy chemical elements.

As the universe aged, gas was continually pulled into the

dark matter halos. Over time, the pressure of the gas eventually came to be important and hydrodynamic effects began

to compete with gravity in controlling the formation of

galaxy-sized structures. The pressure in a gas depends partly

on its temperature, influenced in turn by radiative cooling

(depending sensitively on the history of heavy elements

production by the first stars), and photoionization heating

from the first stars and quasars. Shock waves would have

formed in the supersonic infall of fresh gas into the dark

matter gravity wells, further heating the gas. Gravitational

tides exerted by neighboring structures would have applied

torques to both the gas and dark matter, contributing to

rotational support of the gas against gravity in these early

protogalaxies. As the dark matter gravity wells coalesced

and merged within the cosmic web, small protogalaxies

collided and merged to form larger and larger structures—

this hierarchical description of galaxy formation is strongly

supported by both theory and observation.

Understanding the formation of the first generation of

stars will require continued theoretical modeling of the

hydrodynamics, thermodynamics, and non-equilibrium

chemistry of pristine hydrogen and helium gas in the evolving cosmic web of dark matter. Trace amounts of molecular

hydrogen provide the dominant coolant of the gas in the

initially smaller mass dark matter gravity wells with virial

temperatures below 10,000 kelvin. The formation of this

molecular hydrogen depends sensitively on the free electron abundance and therefore the exact ionization state of

the gas. This in turn will evolve quickly once the first stars

form. Larger dark matter wells with higher virial temperatures will have mostly ionized hydrogen and be able to cool

much more efficiently. Detailed theoretical modeling of

these processes, supported by the Origins Research and

Analysis (R&A) program, will be required to make predictions to guide observations by Origins missions.

Direct detection of the first generation of stars will

almost certainly require the unprecedented sensitivity of

the James Webb Space Telescope (JWST). These stars are

likely to be in clusters of approximately 106

 solar masses.

O B J E C T I V E O N E

Hydrodynamic

simulation of the

cosmic gas density

at redshift 3, for

a sample box

8 million light-years

on a side. These

dense filaments are

detected as the

Lyman-alpha forest

in absorption-line

spectra of distant

quasars.
5

Very deep imaging of a single field with week-long exposures in multiple near-IR filters should be able to detect

even modest birth rates of stars out to redshifts z = 20.

Various spectral signatures will be able to test whether

these are the very massive, hot, short-lived stars that theorists are now predicting, as opposed to a first generation

with a full mass spectrum. JWST will also observe the first

supernovae directly—these can be distinguished from

starlight by their sudden appearance and slow decay. It

should also be possible to investigate the dispersal of the

first heavy elements by looking for the emission lines such

as [OΙΙΙ] predicted to be in the light from the earliest star

forming regions.

The epoch of the first stars and supernovae is not likely

to be uniform throughout the early universe. In the denser

pockets, we may find evidence that the birth of the earliest

stars lies beyond our current observational reach. In other

regions, we may discover pristine, primordial gas and direct

evidence of the earliest star formation. Deep surveys by

JWST will provide an unbiased and statistically valid picture

of the first epoch of stars and their chemical legacy.

INVESTIGATION 2

Observe the enormous release of energy during the

building of the first massive black holes that combined with energy from the first stars to change the

structure of the early universe.

Because they are so bright, quasars turn out to be the most

distant (and therefore earliest) discrete sources of light that

have been observed so far in the universe. Light from distant

quasars is therefore routinely used to probe the evolution

of gas between galaxies (the “intergalactic medium”). Spectroscopic observations by ground-based telescopes and

the Hubble Space Telescope (HST) have used absorption by

neutral hydrogen to trace the evolution of neutral gas in

the cosmic web. Most of this gas is now ionized, however,

whereas the very existence of the cosmic microwave background implies that electrons and hydrogen and helium

O B J E C T I V E O N E

Artist’s impression

of the universe at age

1 billion years. The

scene is dominated

by starburst galaxies

with bright knots

of blue stars and

hot bubbles from

supernova explosions.
6

nuclei combined to form neutral atoms early in the history

of the universe. Something therefore reionized the intergalactic medium, almost certainly ultraviolet and/or X-ray

photons from the first stars and quasars. This reionization

heated the gas and altered its chemistry, thereby affecting

its ability to accumulate into dark matter gravity wells and

form later generations of stars and black holes. We do not

yet know when this reionization epoch occurred, although

there are tantalizing recent observations of the most

distant quasars suggesting that the process may have

been completed as late as redshift z = 6. We also do not

know in detail how ionization occurred, and what were

the relative contributions of starlight and quasars—JWST

will be our primary investigative tool.

Massive black holes are now known to be ubiquitous in

the nuclei of all large galaxies in the present day universe.

The masses of these black holes are tightly correlated to

the larger scale random motions of stars in these galaxies, providing a clear indication that the structure of

galaxies and the presence of black holes are intimately

related. We do not know how this observed relation

arose, and resolving the mystery will require observations of black holes in the process of formation. The

optical and ultraviolet light from these earliest quasars

will be redshifted into the near infrared (IR), and if dust

enshrouds these objects then they will also be copious

sources of mid-infrared radiation. Quasars can be distinguished from star forming regions because they also

produce relatively greater quantities of X-rays. Deep

imaging surveys across the electromagnetic spectrum

are therefore the best way to search for and interpret

these early sources. This is already being done with HST

O B J E C T I V E O N E

A simulated spectrum

of the Lyman alpha

forest in a quasar at

redshift 7. The upper

panel represents an

extrapolation of the

cloud statistics, and

the lower panel

shows the effect of

increasing the cloud

density beyond

redshift 6: the

reionization epoch.

1

0.5

0

1

0

0.5

Normalized Flux

0.8 0.85

Lyβ

Damping Wing

0.9 0.95 1 1.05

Observed Wavelength λ (μm)

zi

 = 6 ze = 7

R = 100, S/N = 10
7

and Chandra, but to push to the earlier epochs we will

require high-sensitivity detections in the near-to-mid-IR.

This next generation of surveys will begin with the Space

Infrared Telescope Facility (SIRTF) and be carried to unprecedented depths by JWST.

Once the earliest sources are detected, JWST will use

them as spectroscopic probes of the intervening intergalactic medium. Theoretical modeling of both quasar and galaxy

formation, funded by the R&A program, will be crucial for

interpreting this data. The exact time interval of hydrogen

reionization will be determined with JWST through high

signal-to-noise observations of the red damping wing of the

Lyman-alpha absorption (Gunn-Peterson) trough in spectra

of very high redshift sources. The shape of this damping

wing can be used to directly measure the Lyman-alpha

absorption optical depth and therefore the neutral hydrogen density. These and similar measurements will probe the

evolutionary history of the gas, and provide a better understanding of the relative roles of stars and quasars during the

reionization epoch.

This complex evolution is accompanied by ongoing star

formation that illuminates the early protogalaxies. In addition, infall of gas into massive black holes produces quasars

and less luminous active galactic nuclei (AGN). Observations

of high redshift star formation and active galactic nuclei by

HST and JWST will allow us to trace the buildup of galaxies

with time. Dust formed by early generations of stars will also

absorb and reradiate starlight and quasar light into the midand far-IR, making observations by SIRTF and JWST crucial to

tracing the energy budget of galaxy formation and early

evolution. Weak gravitational lensing of high redshift galaxies, observed with HST and eventually JWST, will be used to

measure the mass distribution of foreground dark matter

haloes. These observations can then be used to test theories

of the evolution of the invisible framework of the cosmic

web. JWST will be a powerful tool for the technique of gravitational lensing to chart the clustering of dark matter from

galaxy halos to the much more massive galaxy-cluster halos.

The gas component of the cosmic web, for z > 3, would

be observable in great detail with a next-generation

ground-based telescope such as the Giant Segmented

Mirror Telescope (GSMT). The enormous light-gathering

power of such a telescope allows the use of faint galaxies as

the probes of intergalactic absorption. Unlike quasars, these

background galaxies are sufficiently numerous to probe the

cosmic web with the required resolution to see structure

growth at the correlation length. The ability to follow the

gas evolution of the cosmic web from z = 3 down to the

present day will be greatly enhanced by the Cosmic Origins

Spectrograph on HST, but a larger UV-optical space telescope, with far more efficient UV detectors, will be essential

for a thorough understanding.

INVESTIGATION 3

Describe the assembly of galaxies and their subsequent evolution from generations of stars, leading

to the diversity of galaxies in today’s universe.

The buildup of the stellar component of galaxies will be

measured with present and future surveys across a wide

range of wavelengths, with HST, SIRTF, and JWST playing key

roles. HST and SIRTF observations of young galaxies will

measure star formation rates and the accumulation of older

stars in these systems. A substantial fraction of star formation may be hidden by dust, and deep mid-infrared imaging

by SIRTF will be able to detect dust-enshrouded star forming regions out to z = 2.5, as well as possible dust-hidden

AGNs. Complementary wide-field surveys in the near and

mid-infrared will also be conducted by SIRTF in order to

connect the evolution of galaxies with the growth of the

large-scale structure that follows the evolution of the distribution of dark matter.

The deep JWST images designed to detect the first stars

and quasars will also image large numbers of galaxies in the

z = 1 – 5 redshift range that can be followed up with JWST

and ground-based spectroscopy. Because of its much

greater aperture, JWST will reach much fainter systems than

HST and SIRTF, crucial for understanding the complete star

formation history of the universe. JWST’s spectroscopic

capability will provide a powerful probe of the buildup of

the heavy elements. Moderate-resolution spectroscopy

(R=1000) in the rest-frame 3500–7000 angstrom range can

be obtained for thousands of galaxies to provide a uniform

sample of heavy element abundances, stellar ages, starformation rates (from emission lines of HΙΙ regions), and

measurements of the level of dust extinction. JWST

spectroscopic observations of higher resolution (R = 3000),

O B J E C T I V E O N E
8

possible for luminous galaxies, can measure stellar and gas

kinematics and provide information on galaxy masses and

further detail of the process of galaxy assembly. Spatially

resolved spectroscopy of bright galaxies with interesting

morphologies will probe the spatial variations in physical

conditions in these systems. Complementary measurements

for lower-luminosity galaxies over this epoch could be done

with the next generation of larger ground-based telescopes

(for example, the proposed 30-meter GSMT) using laser

guide star adaptive optics and sufficiently high spectral

resolution to overcome night-sky emission. Imaging and

spectroscopy of high redshift galaxies in rich clusters,

groups, and the field will provide the data needed to

describe the effects of environment on galaxy formation

and evolution.

The dust content of typical galaxies at high redshift is

acknowledged as a vital and largely unexplored aspect of

galaxy evolution. Observations with ISO and the SCUBA

instrument on the James Clerk Maxwell Telescope have

partially resolved the submillimeter background discovered

by COBE into galaxies, providing strong evidence that much

of the light generated by high redshift star formation is

reprocessed by dust. SIRTF will undoubtedly detect more

of the sources contributing to the background. JWST can

measure even heavily dust-enshrouded star formation out

to redshift z = 3.5 by detecting rest-frame 3.3-micron polycyclic aromatic hydrocarbon (PAH) emission. In addition,

JWST can exploit numerous mid-IR spectroscopic diagnostics to distinguish star formation from hidden AGN. These

include coronal lines of silicon, sulfur and calcium as well as

rotation-vibration emission of molecular hydrogen.

The goal of this part of the Origins program is to understand how the first stars and black holes began the process

of assembling the galaxies we see today. It will be essential

to connect what we learn with observations of nearby galaxies. Measuring the rate at which stars formed at different

times in the history of the universe will allow us to account

for the integral population of stars and stellar remnants

(white dwarfs, neutron stars, and black holes) that we

observe around us today, as well as the overall abundance

of heavy elements that were produced by these stars. Detections of high redshift supernovae and the determination of

the variation in supernova rate with time will provide a

complementary measurement of the star-formation rate.

Because certain classes of supernovae come from the most

massive stars, this will also help us trace the rate at which

stars of different masses form, which may help answer

the question of whether the initial mass function of star

formation is a function of environment and/or time. Highresolution spectral observations with ground-based telescopes of giant stars in Local Group galaxies can also

provide a cross check to the yields of r- and s- process

elements produced by different kinds of supernovae.

The stellar populations laid down in earlier epochs comprise the fossil record of stars in our own galaxy and its

neighbors. The high spatial resolution of HST over a substantial field has been crucial for producing color-magnitude

diagrams that, when combined with theory, validate the

history of star formation that will be carefully charted with

lookback observations of HST, SIRTF, and JWST. It will be

important to extend our capabilities to larger apertures and

higher spatial resolutions in order to reach other galaxies, to

the main-sequence turnoff for the Milky Way’s neighbors,

and down to the giant and horizontal branches as far as the

Virgo cluster. JWST will extend these studies beyond the

reach of HST, but a larger HST descendant that images in the

UV-optical would make a decisive contribution to this effort.

Diffraction-limited, high-strehl-ratio imaging over modest

fields would provide an essential, unique capability only

achievable from space.

The morphology of today’s mature galaxies is described

by the Hubble sequence—a variety of distinct morphological types including irregulars, spirals and ellipticals—and

these morphologies consist of basic structural components

such as disks, bulges, bars, and spiral arms. There is now

good evidence that the Hubble sequence arose between

1 < z < 3, but as yet there are no observations to guide

modeling of how the morphology and structures of galaxies

arose and evolved. The high angular resolution and sensitivity of JWST will permit direct observations of the morphological evolution of galaxies as well as the history of galaxy

collisions and mergers over this crucial epoch.

O B J E C T I V E O N E
9

How do different galactic ecosystems (of stars and gas)

form and which can lead to planets and living organisms?

Research Area Two

Earth and its solar system siblings are made of

ices from the carbon-nitrogen-oxygen family of elements and rocks from the calcium, silicon, magnesium, and iron groups. Life, as we know it, depends

entirely on the complex chemistry of compounds

built around carbon atoms, what we call “organic”

compounds. We now know that the universe was

not born with these materials, but that the stars

themselves are the sites of their manufacture. This

discovery—that the heavy elements essential for a

living being come directly from stars—ranks among

the greatest human achievements in understanding

the universe and our place in it.

The buildup of these heavy elements did not

happen all at once. We have learned how these

elements are made in stars and how they can be

recycled into future generations of stars and potential planetary systems. At the ends of their lives

massive stars explode and less massive stars slowly

shed gas enriched with these heavy elements. In

each cycle the abundance of heavy elements increases as the “ash” of nuclear burning in the centers

of stars is added to the mix. We now know that this

enriched gas remains bound to a galaxy by gravity,

at least for giant galaxies like our own, and that

this store slowly increases over time. We can even

roughly chart the increase in heavy elements over

the generations of stars born over the 12 billionyear lifetime of our Milky Way Galaxy and compare

it with the process in other nearby galaxies.

However, we know relatively little detail of the

enrichment process for interstellar gaseous material

in our galaxy and others. When and how did the

process of chemical enrichment begin, and what

kinds of influences regulated the process? What

exactly is the importance of heavy elements (in gas,

molecules, and dust) for the formation of planets?

Which elements are essential? For example, is there

a minimum mass in long-lived radioactive elements

needed for a geologically active planet such as

Earth? Is there a threshold level of heavy elements

necessary for planet formation? Do the abundance

gradients in our own galaxy or others result in a

“galactic habitable zone” where the formation of

Earth-like planets is favored? Has the course of

planet building changed over cosmic time as the

abundance and balance of these heavy elements has

grown? We can now begin to answer such questions

by finding out whether the presence and character

of planetary systems depends on the heavy element

abundance of parent stars; for example, do stars

with the lowest abundances, in the globular clusters

of the Milky Way or in its outer halo, have well

developed planetary systems? We can investigate

whether the dust grains and complex hydrocarbons

found in galactic clouds and star-forming regions

survive to play a role in the formation of planets

and their atmospheres, or whether instead they are

vaporized in the process and remade in the later

stages of planet building. Such studies will teach us

how the development of giant star systems like the

Milky Way is essential to the eventual emergence

of life, how long our galaxy has been inhabited,

and where we may look in our own galaxy to find

other life.

We highlight two investigations in this area:

• Study how the lifecycles of stars in the Milky

Way and other galaxies build up the chemical

elements and galactic environments needed for

planets and life.

• Observe when and where habitats for life

emerged in the Milky Way and other galaxies.

O B J E C T I V E O N E
10

properties of 75 nearby galaxies in order to correlate star

formation rates with properties of the interstellar medium

and JWST will extend such work to a far larger sample.

We also need to study how the star formation rates and

elemental abundances of galaxies evolve over time, by

looking at samples of galaxies at different cosmic distances

(that is, at different look-back times). This will give us insight

into the conditions in our own galaxy 5 billion years ago

when Earth was formed. Large ground-based telescopes

such as GSMT will make crucial spectroscopic studies of

stars that record the fossil record of stellar birth in our galaxy and its neighbors to compare with the results of these

lookback studies. The external environments of galaxies also

play an important role in star formation. Galaxies rarely

evolve in isolation—galactic ecosystems are not “closed

boxes”—and mergers of galaxies affect their gas content,

star formation rate and structural evolution. Galactic winds

and the infall of clouds of gas and dust into large galaxies

also act to modify the elemental abundances of the intergalactic medium and the interstellar medium in galaxies. We

know that galaxies underwent many more mergers in the

past, so we need to study galactic environments as a function of look-back time. This work will require large aperture

telescopes and sensitive spectrographs operating from the

UV to IR. These investigations will be enabled by JWST,

Single Aperture Far-Infrared Observatory (SAFIR), and a HST

O B J E C T I V E O N E

The nearby galaxy

NGC 4214 is lit up by

filigreed clouds of glowing

gas surrounding bright

stellar clusters. Their hot

blue stars eject fast stellar

winds, moving at thousands of kilometers per

second, which plow out

into the surrounding gas.

INVESTIGATION 4

Study how the lifecycles of stars in the Milky Way and

other galaxies build up the chemical elements and

galactic environments needed for planets and life.

A galaxy may be thought of as a giant ecosystem containing

stars, radiation, dust, gas, and planets. Much like ecosystems

on Earth, the interactions among these elements are complex. As yet we know very little in detail about how galactic

ecosystems work, and how they produce planets and life,

but future Origins missions will shed much light on this

process.

One of the least understood processes in the galactic

ecosystem is the interaction between the stars and gas—

massive stars and supernovae inject enormous amounts of

mechanical energy through flows and shocks and by radiation into the gas. This stirs the gas and forms structures

called superbubbles and fountains. Though these facts are

clear, we have little understanding of the effect of this “feedback” on subsequent star formation and, hence, the buildup

of heavy elements necessary for life.

The full picture of star formation in the present-day

universe will emerge only when we have studied the formation of stars in a sample of galaxies with a diverse range of

mass, gas density, dust content and elemental abundance.

SIRTF will, for example, characterize the large-scale infrared
11

O B J E C T I V E O N E

Hubble Space

Telescope image of

the center of the

globular star cluster

Omega Cen. The very

high density of stars

makes this an ideal

laboratory for

studying interactions

among stars.

have shown that the mix of different heavy elements has

changed dramatically over the history of the Milky Way and,

by implication, for other galaxies as well. By investigating

the incidence of planets and, ultimately, life, in various regions of our galaxy we will be able to determine the necessary galactic environmental conditions for the formation of

planets and life.

Such investigations have already begun. An extensive

observational search with HST for planetary transits of stars

in the ancient globular cluster 47 Tucanae turned up no

planets, even though the search had considerable sensitivity. Could it be that the low heavy element abundance of

globular clusters precludes the formation of planets, or

might encounters between neighboring stars in such dense

stellar systems disrupt planetary systems or prevent them

from forming in the first place? Future observations and

theoretical investigations within the Origins program will

address such questions as how the presence of terrestrial

and giant planets is related to stellar mass and age, magnetic activity in the star, binarity and/or the presence of

surrounding stars in a cluster, and the overall galactic environment in which the star formed. For example, SIRTF, JWST,

and eventually next-generation near-to-far-IR space telescopes will be able to observe planet formation in a wide

range of environments.

These modest studies are only the beginning. In the far

future one can imagine extending some elements of the

search for planets beyond our own galaxy. For example, can

observations of infrared emission from young stars in dwarf

galaxies with low abundances of heavy elements tell us, by

analogy to similar, higher resolution and higher sensitivity

observations of Milky Way stars, whether such galaxies could

have planets and life? More extensive studies of their histories of star formation and heavy element abundances will

tell us, in comparison with the Milky Way, whether planet

building is likely to have proceeded differently in different

types of galaxies. Through exhaustive study of the relatively

nearby stars and detailed studies of the stellar populations

far from our neighborhood, we may eventually connect the

incidence of planets and the potential for life to the global

properties of galactic environments.

descendent. Measurements of absorption lines in the spectra of background X-ray sources by Chandra and Constellation-X will also measure heavy element abundances in the

interstellar media of galaxies, independent of whether these

elements exist in the gas phase or are locked up in solid

dust grains.

INVESTIGATION 5

Observe when and where habitats for life emerged in

the Milky Way and other galaxies.

Our solar system orbits the galaxy at a distance of roughly

24,000 light-years out from the center; currently it is the only

known system to contain life. Is our location a coincidence,

or is this region of the galaxy more hospitable to the formation and evolution of life? In other words, is there a galactic

habitable zone much as there is a habitable zone around a

star? Sampling from the central regions of our galaxy to its

periphery, both star formation rates and heavy element

abundances are seen to decrease. It is conceivable that there

is a minimum heavy element abundance necessary for the

formation of both terrestrial and giant planets as well as for

life, and that this abundance does not exist in the outer

regions of the galaxy. It is also possible that various mixes of

heavy elements, particularly radioactive ones, are important

for the formation of a world with plate tectonics, and that

this is important for the evolution of life. Recent studies
2

The center of our

Milky Way Galaxy

at a distance of

25,000 light-years,

visible in the top left

corner. The Milky

Way contains about

100 billion stars,

one of them is the

Sun. Only a fraction

of the galaxy is

captured in this

image covering

about the same

area as a fist held

out at arm’s length.

Image: NASA/

2MASS

CHAPTER

Stars

and Planets
13

O B J E C T I V E T W O

During the past three decades, we have used both ground- and space-based facilities to look inside the

nurseries where stars and planets are born. Parallel studies conducted in the solar system with planetary

probes and of meteorites have revealed clues to the processes that shaped the early evolution of our own

planetary system. An overarching goal of science in the 21st century will be to connect what we observe

elsewhere in the universe with objects and phenomena in our own solar system.

We now have strong evidence, based on the telltale wobbles measured for nearly 100 nearby stars,

that they are orbited by otherwise unseen planets.

One remarkable star, Upsilon Andromedae, shows

evidence for three giant-planet companions. For

another, HD209458, astronomers have observed

the periodic decrease in its brightness due to the

transit of one of its planets across the stellar disk

and have thereby been able to measure the planet’s

radius and mass. However, these newly-discovered

planetary systems are quite unlike our own solar

system. The masses of the extrasolar planets span

a broad range from one-eighth to more than ten

Jupiter masses. Many of the planets are surprisingly close to their parent stars and the majority

are on eccentric orbits. Extreme proximity and

eccentricity are two characteristics not seen in the

giant planets of our solar system. Although planetary systems like our own are only now becoming

detectable with the techniques used to discover

the new planets, the lack of a close analog to our

own solar system and the striking variety of the

detected systems raises a fascinating question:

Is our solar system of a rare (or even unique) type?

In tandem, astronomers have now identified

the basic stages of star formation. The process

begins in the dense cores of cold gas clouds

(so-called molecular clouds) that are on the verge

of gravitational collapse. It continues with the

formation of protostars, infant stellar objects with

gas-rich, dusty circumstellar disks that evolve into

adolescent “main-sequence” stars. These more

mature stars are surrounded by tenuous disks of

ice and dust that remain after most of the disk

gas has dispersed. It is in the context of these last

stages of star formation that planets are born.

The objective of understanding the parallel

development of stars and planets and determining the prevalence and demographics of planetary

systems will focus on two critical areas:

• Tracing the path from gas and dust to stars

and planets.

• Detecting planetary systems around other stars

and understanding their architectures and

evolution.

...to learn how stars and

planetary systems form and evolve.

13
14

SOFIA (the Stratospheric Observatory for Infrared Astronomy) is

expected to start carrying scientists and teachers into the stratosphere late in 2004. But SOFIA

educators are already helping

middle-school students gain a

better understanding of one of

the most fundamental aspects

of modern astrophysics—objects

in space emit a lot of energy that

the human eye can’t see.

Learning about “Invisible” Light

concepts of invisible light. Working with a team from Montana

State University at Bozeman,

they developed four activities

which use common household

electronics, like television remote

controls and video cameras, or

readily available inexpensive

parts such as IR LEDs, IR-sensitive

photocells, filter gels, etc.

Written drafts of the activities

were submitted to the Origins

Forum evaluation team, which

used experienced peer reviewers-teachers to check the activities for conformance to national

standards, pedagogy, and practicality. After their comments were

incorporated, the SOFIA team

assembled 20 sets, including kits

with all the needed small elecO B J E C T I V E T W O

tronics parts, and distributed

them to volunteer teachers

around the country who tested

the activities in science classrooms with their students and

returned valuable feedback.

Even before teachers start flying

aboard SOFIA, thousands of

students are learning about

“invisible light,” and why it is so

important to our understanding

of the universe.

14

“Active Astronomy: Classroom

Activities for Learning About

Infrared Light” engages students

in four standards-based activities

that help them understand that,

when it comes to electromagnetic energy, there really is more

out there than meets the eye.

In surveying the educational

landscape, SOFIA staff discovered

there were many existing classroom activities dealing with

visible light and color, but very

few which attempted to teach
15

Research Area Three

How do gas and dust become stars and planets?

The themes of this research area are the comprehensive study of the origin of stars in molecular

clouds, the formation and early development of

stars of all types, the formation of planets in their

protostellar cradles, and the characterization of

protoplanetary dust and gas disks. The goal is to

trace the evolution of stars and planets from birth

to maturity.

 Molecular clouds both provide the raw material

for production of stellar embryos and are the nurseries of newborn stars and planetary systems.

The process of star formation involves a complex

interplay, still poorly understood, between gravitational, turbulent, and magnetic forces within dense

clouds. Upon collapse, just-formed stars produce

energetic outflows and intense radiation fields

which drive shocks and ionization fronts back into

the surrounding medium, thereby providing feedback that can affect cloud structure and chemistry,

and, hence, future generations of young stars.

Moreover, the raw material from which planetary

systems form contains the heavier elements in the

same diverse states of molecular complexity found

in the parent molecular cloud. Chemical processes

at work during star and planet formation which can

further modify this inventory include gas-phase

reactions as well as reactions in and on coalescing

planetesimals. Ultimately these compounds, including potentially important biogenic species, whether

produced in the nebula or accepted unchanged

from the interstellar medium, are incorporated into

the material that becomes the planets, satellites,

asteroids, and comets. Thus, the compounds that

emerge from the interstellar/protostellar crucible

provide the seeds from which life must spring.

A central question is: How did the chemistry

reach a complexity that made life possible?

By fragmentation and possibly also through

merging, the objects formed from molecular

clouds exhibit a wide variety of masses and multiplicities. These range from single stars and loworder multiples formed in relative isolation, for

example, the T Tauri triple star system, to dense

clusters of stars and brown dwarfs spanning four

orders of magnitude in mass such as the Orion

Nebula Cluster. Our stellar system (the Sun) has

only one average-mass star, though it is strongly

suspected that the Sun was born—like most

stars—in a sizable cluster. An important goal in

this research area is to understand how the mass

distribution of stars (the “initial mass function”)

emerged and how the number, mass, and environment of stars figures into the formation of planets

and, ultimately, life.

To understand planet birth and growth

requires the protoplanetary disks that encircle

protostars.There is observational evidence for

two disk constituents: gas, primarily molecular

hydrogen, and dust, including grains of interstellar origin and those formed in situ. A natural

question is: How does dust and gas accumulate

into mature planetary systems?

The Origins theme will:

• Investigate molecular clouds as cradles for star

and planet formation.

• Study the emergence of stellar systems.

• Determine how protoplanetary dust and gas

disks mature into planetary systems.

O B J E C T I V E T W O
16

O B J E C T I V E T W O

Major stages in the

formation of stars and

planetary systems from

the densest cores of

molecular clouds, based

on an original sketch by

Frank Shu. Each of these

transitional states yields

characteristic signatures

that can be observed.

1 pc

t = 0

Gravitational collapse

10,000 AU

t~104

 – 105years

Protostar, embedded

in 8,000 AU envelope,

disk, outflow

t~105 –106years

T Tauri star, disk,

outflow

100 AU

t~106 –107years

Pre-main-sequence

star, remnant disk

100 AU

t > 107years

Main-sequence star,

planetary system (?)

50 AU

Dark cloud cores

INVESTIGATION 6

Investigate molecular clouds as cradles for star and

planet formation.

Opaque to optical photons, molecular clouds achieve

densities much higher than those of the diffuse interstellar

medium. Deep within these “dark” clouds a rich range of

chemical reactions is supported, including the creation and

depletion of heavy elements onto dust grains and into ices.

We know relatively little of the overall enrichment process

for interstellar gaseous material in the universe, whereas

explanation of how stars synthesize new elements through

nuclear reactions was one of the great triumphs of science

in the 20th century. Comprehensive understanding of

heavy element creation and depletion and the important

role of dusty material in star and planetary system formation is required in order to understand the chemical conditions from which life on our planet later arose. We must

study dust formation and destruction, dust content in our

own and other galaxies spanning a wide range of heavy

element abundances, the influence of recently formed

stars on the ambient cloud, and the effects of varying

molecular cloud chemistry on star and planetary system

formation.

The above investigations can be pursued with spectroscopic studies of the interstellar medium that probe molecular cloud chemistry. Also, observations of dust, either

directly via its thermal infrared emission or indirectly

through the extinction of background sources, and dust

spectroscopy are required. A large-aperture ultraviolet/

optical telescope will permit spectroscopy of the interstellar medium, cloud extinction maps, and detailed
17

O B J E C T I V E T W O

Disks of dust encircling

young stars provide a

view of the formative

stages of the building

of planetary systems.

Images of disks seen in

various orientations

allow estimates of

the disks’ size, shape,

and thickness.

study of jets and outflows. In the mid- to far-infrared

(30–300 micrometers), first SOFIA and Space Infrared

Telescope Facility (SIRTF), and later a large-aperture spaceborne telescope will be able to determine the temperature, density, and velocity structure of molecular clouds

and collapsing cloud cores by mapping the emission from

the dominant gas coolants (OΙ, H2

O, C+, high-J CO lines)

as well as the dust-generated continuum. At longer

wavelengths, high spectral resolution submillimeter

(300–650 micrometers) investigations with SOFIA will

reveal infall kinematics and protostellar chemistry. ALMA

will elucidate molecular cloud characteristics through

high-J CO and more complex molecules. In order to provide clues concerning the earliest phases of star formation,

these continuum and spectral line observations must

be conducted at angular resolutions of 0.1–1 arcsec

(10–100 astronomical units in the nearest star-forming

regions). JWST will be able to probe the most central

regions of protostars.

Where, when, and for how long do stars form in molecular clouds? Is star formation a fast process as recent

evidence suggests, or one that occurs on the slow pace of

particle drift along the magnetic field lines that thread

molecular clouds, as theory has long predicted? Why do

certain regions or neighborhoods in clouds produce stars,

while others do not? Understanding these different modes

of star formation will require the continuation of a vigorous R&A program that investigates the chemistry, physical

structure, turbulent and magnetic effects, and fragmentation processes of molecular clouds. Furthermore, the

chemistry in molecular clouds is quite exotic by terrestrial

standards and targeted laboratory studies of materials

under conditions that mimic—as much as possible—the

appropriate cosmic environment are essential.

INVESTIGATION 7

Study the emergence of stellar systems.

Gravitationally bound multiple star systems (e.g., binaries)

are thought to form by fragmentation, induced by rotational effects during the collapse of a single molecular

cloud core. In order to explain the diversity in orbital periods, eccentricities, and mass ratios observed in binary star
18

INVESTIGATION 8

Determine how protoplanetary dust and gas disks

mature into planetary systems.

It has been determined observationally that stars accrete

material from disks and that disks around young stars have

finite lifetimes that range from perhaps one to several tens

of millions of years. However, many aspects of this schematic picture remain unclear and the history of the gas

content in disks, though critical, is insufficiently understood. Moreover, the flow of material during stellar accretion is inward toward the star. This flow would naturally

carry any nascent planets with it. How then do the planets

survive? Crucially, the timescale for the disappearance of

gas may determine whether planets can form and survive

at all. The most abundant species in protostellar disks is

molecular hydrogen. However, its quantity until now has

largely been inferred from trace species such as carbon

monoxide, which may not be a proper tracer of total gas

throughout the lifetime of the disk. Hence, direct measurements of molecular hydrogen, via infrared spectroscopy

with SIRTF, SOFIA, and Single Aperture Far-Infrared Observatory (SAFIR), are needed to directly probe gas disks.

Furthermore, evidence from our own solar system suggests that the chemical composition varies with location

in the disk. High angular resolution studies in the nearinfrared (SIRTF, JWST) and far-infrared (SIRTF, SOFIA) are

necessary to trace the distribution of important planetary

constituents such as water ice, silicates, and complex

carbon molecules.

Near the end of the evolution of a mature disk-planet

system, the remnant disk gas is dispersed, leaving behind

planets and the rubble of many smaller bodies. Dust produced in collisions of asteroid-like debris is thought to

form the low-mass disks that have been detected around

more mature stars, such as Vega. SIRTF will give us our first

hints concerning gas and dust dispersal, but follow-on

large space-based telescopes such as JWST and SAFIR are

ideally suited to track the evolution and map the structure

of vestigial debris disks around nearby main-sequence

stars.

O B J E C T I V E T W O

Hubble finds

young stars in a

cosmic dance.

One star of a trio

of newborn stars

emits oppositely

directed streams

of glowing gas

12 light-years

long. Pulses in the

gas flow create

the fine structures

in this IR image.

systems, an understanding of the physics of fragmentation

is needed. Fragmentation at even earlier stages is responsible for star cluster formation. Observations show that the

result of this process can be small groups or aggregates of

10–30 stars, ranging to large clusters of up to 10,000 or even

100,000 stars. The relationship between the stars and star

clusters that are formed and the initial conditions in the

parent cloud is not at all understood.

In order to achieve the scientific goals listed in this investigation, deep imaging and spectroscopic surveys from the

ground, in the air with SOFIA, and from space with SIRTF and

the James Webb Space Telescope (JWST) will be crucial.

These missions will quantify the statistical properties of star

clusters and lead us to an understanding of the star formation environment most likely to have hosted our own protosun. Moreover, advances in laboratory astrophysics are

needed to understand chemical evolution in the circumstellar environment. A strong R&A program is essential to investigate the formation and properties of circumstellar disks

around both single and multiple star systems.
19

Research Area Four

Are there planetary systems around other stars and how do their

architectures and evolution compare with our own solar system?

A cornerstone of the Origins program is the discovery of planets and planetary systems. Along

with their discovery comes the determination of

the numbers, distributions, and orbits of planets

in the solar neighborhood. How many planets

are there and around what types of stars are they

found? Are other planetary systems similar to our

own? This research area is an ambitious one for

both observation and theory. Our efforts have

begun with indirect detection of planets by measuring the radial velocity perturbations conferred

by their gravitational pull on their parent stars.

Soon, ground-based and space-based interferometers will add an important dimension to indirect

detection by measuring the periodic shift in position of a star on the sky (astrometry) induced by

its planets. With this additional information, the

orbits of planets can be deduced—even those of

complex systems with multiple planets—leading

to accurate measurements of the planetary masses.

The large star-planet brightness ratios—a million in the mid-IR and a billion in the visible—

make their direct detection a technical challenge

beyond anything attempted to date in astronomy.

Astronomers will need to build high-precision

telescopes to accomplish the separation of the

light from star and planet for even the nearest

few hundred stars, at distances of no more than

20 parsecs. Eventually, statistically valid samples

will require extending to many times that distance,

meaning that the challenge of exploring the solar

neighborhood for other worlds—already daunting—has just begun.

As we plan, test, and build instrumentation

capable of detecting planets as small as Earth

around nearby stars, there is much work that can

be done now to improve our scant knowledge of

other planetary systems. It is now possible to survey for the largest planets, down to the masses

of Jupiter and Uranus by both indirect and direct

means. Hence, an inventory of neighboring stars

for such giant planets is a key goal of the Origins

initiative. A related goal is to find “solar-system

analogs,” planetary systems with giant planets on

near-circular orbits many astronomical units (AU)

in size. Another crucial study will be to determine

how common are smaller planets such as Earth,

something that can be done, surprisingly, more

easily for stars at considerably greater orbital distances than the Earth-like worlds we eventually

hope to find and study in detail.

To accomplish these goals, present and future,

the research in this area is sectioned into two

investigations:

• The search for evidence of planets in disks

around young stars.

• The census of planetary systems around stars

of all ages.

O B J E C T I V E T W O
20

O B J E C T I V E T W O

 INVESTIGATION 9

Search for evidence of planets in disks around

young stars.

The initial steps toward planet formation occur in the surrounding disk of material that avoids either falling into a

forming star or being ejected in outflows. These steps are

now occurring around young stars in nearby molecular

clouds. They should be apparent through their effects on

the structures of the disks, but are hidden from view by a

combination of obscuration due to the surrounding dust

and limitations in resolution that mask the details in those

young disks we can observe. Over time these observational

limitations will be overcome through larger aperture telescopes and interferometers.

The most likely chemical constituents of the disks, including simple organic compounds that are the raw material for

life, have characteristic absorption features accessible to

JWST. In the near infrared, JWST will penetrate the obscuration to image these disks and map the distribution of disk

materials on scales down to about 6 AU. With these images,

we will fit disk model parameters, such as disk scale height

(flaring), outer radius, and grain optical properties. These

constraints provide the initial conditions necessary for

studying the origin of planetary systems.

As planets form from the dust disk, they can interact

gravitationally with the remaining gas. For relatively small

planetary masses (10–100 Earth masses), this interaction

results in density waves; for masses comparable to that of

Jupiter, it results in the opening of gaps in the disk, with a

radial extent of a few tenths of an astronomical unit or

greater. These disk signatures may serve as proxies for the

underlying planet, which may be much more difficult to

detect directly. The resolution of JWST will allow an initial

survey for large gaps in young disks. However, the detection

of a gap associated with a proto-Jupiter, 1 AU width at

a distance of 5 AU from a star in a nearby star-forming

region, will require an angular resolution better than

0.01 arcsecond. The gap and planet will be separated from

the star by only 0.05 arcsecond, and for typical disk and

planetary temperatures of a few hundred kelvin, most of

the energy is radiated in the 10-micrometer spectral region.

Interferometric or coronagraphic imaging of disks in nearby

star-forming regions by the Terrestrial Planet Finder (TPF),

will be able to map and characterize these disk structures

and give us an unprecedented view of the planet-formation

process.

Another promising way of studying planet formation in

disks is to find evidence that small dust grains are being

depleted by coagulation into larger grains and eventually

into planetesimals. Observations must distinguish grain

growth from effects caused by radiation blowout and

Poynting-Robertson drag. Spectral and photometric studies,

using JWST and SAFIR, of the temporal development of the

IR spectral energy distributions of the disks around young

stars play central roles in this investigation.

It may also be possible to image young protoplanets

directly, since some theoretical models predict that they

achieve a brightness of 1/1000 to 1/100 that of the central

star during a relatively brief phase of rapid accretion of gas.

A Jupiter-like protoplanet at 5 AU from its star will be

separated from the star by 0.05 arcsecond at distances of

100 parsecs. The starlight nulling or advanced

coronagraphic ability of TPF will be essential to separate the

planetary radiation from that of the surrounding disk and

the star, but the precursor interferometry that will soon be

done from the ground with the Keck Interferometer (KI)

might give us our first tentative glimpse of such an embedded planet.

INVESTIGATION 10

Conduct the census of planetary systems around

stars of all ages.

We must follow-up the initial epoch of giant planet discoveries with an extensive dynamical, photometric, transit, and

imaging exploration of main-sequence stars to determine

the orbital characteristics and gross physical properties of

their planets. A multi-pronged strategy of dynamical, photometric-transit, and imaging techniques should be pursued

in series and in parallel. These should be implemented in

three chronological phases.
21

In the first (reconnaissance) phase, astronomers must

make a complete inventory of giant and Neptune-mass

planets around all stars within 10 parsecs and around a

statistically significant sample of more distant stars. Such a

census, carried out with ground-based radial-velocity and

astrometric techniques, will determine the abundance of

planets and the correlation of stellar properties (such as

mass, metallicity, and binarity) with giant planet properties

(such as mass and orbital parameters). Importantly, giant

planets dynamically constrain the orbits left available to

terrestrial planets, influencing later searches for Earth-like

worlds. In this sense, the study of giant planets is an important stepping stone to the more demanding study of the

smaller terrestrial planets.

The above Doppler and astrometric surveys are challenging, requiring velocity precision of 1 m/s and astrometric precision of 20 microarcseconds (for example, the

Keck Interferometer). Nonetheless, these efforts are relatively inexpensive and the technology is already relatively

mature. Note that the planets detected in this first reconnaissance phase have intrinsic brightnesses of a millionth

to a billionth that of the host star and many will be separated by an arcsecond or less.

A second phase employs the space-telescopes Kepler—

a new Discovery-class mission designed to photometrically search for terrestrial and giant planet transits around

tens of thousands of nearby stars—and the Space Interferometry Mission (SIM), an interferometer with an astrometric precision for terrestrial and giant planet detection

of 1–10 microarcseconds. Kepler will have a photometric

precision of one part in 100,000 and should discover

hundreds of terrestrial and giant planets, while SIM will

discover and astrometrically measure planet masses down

to a few Earth-masses. SIM will survey the youngest stars

close to the Sun to study the formation and evolution of

Jupiter-size planets. To obtain a secure mass for a terrestrial planet requires a dynamical technique such as only

SIM will employ. The complementarity between the photometric-transit technique of Kepler and the astrometricinterferometric technique of SIM provides NASA with a

powerful program for pioneering terrestrial planet

discovery and preliminary terrestrial and giant planet

characterization.

The first and second phases of dynamical and transit

surveys must be followed by a third phase of direct spacebased detection of the reflection and/or intrinsic light

of the planets themselves. For giant planets, the logical

technological and scientific precursor to a Terrestrial Planet

Finder (TPF) and the more difficult problem of direct

terrestrial planet imaging and spectroscopy is a spacebased “giant planet finder.” Using high-contrast imaging

and low-resolution spectroscopy, such a mission would be

capable of both discovery and analysis of the dynamically

dominant and brighter components of planetary systems,

while the later TPF will be able to observe at even larger

star-planet flux contrasts the spectral features of the water,

carbon dioxide, methane, and ammonia thought to reside

in the atmospheres of the terrestrial planets. The technology, management structure, and discoveries of a giant

planet finder program would provide NASA with valuable

experience and guidance as it embarks upon the more

challenging TPF initiative.

Though the direct photometric and spectroscopic

detection of extrasolar giant planets will be a milestone in

planetary research, the discovery and study of Earth-like

planets that would be enabled by TPF is the ultimate goal

of this first era of extrasolar planetary exploration.

Radial-velocity programs are unlikely to detect extrasolar planets with masses below a Uranus mass. Astrometric searches with an accuracy of 10 microarcseconds

(KI) to 1 microarcsecond (SIM) can push the limit down to a

few times the Earth’s mass and survey a volume out to

5–10 parsecs. A space-based photometric-transit survey

such as Kepler will extend to much larger volumes of space

and provide an initial estimate of the frequency of terrestrial planets. However, direct imaging and spectroscopy of

Earth-like planets will require TPF, an infrared interferometer or an optical coronagraph that can suppress the light

of the central star to unprecedented levels, to reveal for the

first time the atmospheres of planets like our own outside

the solar system.

O B J E C T I V E T W O
Habitable

Planets and Life

Artist concept of

the giant planet

and a moon

around HD 209458,

a Sun-like star

located 150 lightyears away in

the constellation

Pegasus. Observations of this system

demonstrate

that it is possible

to measure the

chemical makeup

of alien planet

atmospheres and

to potentially

search for the

chemical markers

of life beyond

Earth. Image:

NASA/HST

3

CHA PTER
23

...to explore the diversity of other worlds and

We have now found many extrasolar planets. Most are unlike those in our own solar system. But might

there be near-twins of our solar system as well? Are there Earth-like planets? What are their characteristics?

Could they support life? Do some actually show signs of past or present life?

search for those that might harbor life.

After centuries of speculation, we finally know that

there are indeed planets orbiting other stars. The

extrasolar planets discovered so far seem to be gas

giants like Jupiter. Earth-like worlds may also orbit

other stars, but to this point our measurements lack

the precision to detect a world as small as Earth.

This could happen before the end of the decade

through a NASA Discovery mission called Kepler,

but even before then, detailed study of giant planets

will tell us much about the formation and history

of planetary systems, including our own. We have

already made a first reconnaissance of the atmospheric properties of one such giant planet, which

fortuitously passes directly in front of its star, allowing us to probe its atmosphere even if we can’t see

the planet directly. Beyond this, new techniques

under development will actually provide images of

these distant solar systems. With direct imaging we

can make more detailed studies of giant extrasolar

planets, helping us to learn whether other Jupitersized planets are near-twins of our Jupiter.

The Kepler mission, focusing on a myriad of

distant stars, will be our first opportunity to find

out how common it is for a star to have an orbiting

Earth-like planet, how big those planets are, and

where they are located in relation to the “habitable

zone” where life as we know it is possible. This

information will shape the follow-on search for

Earth-like planets orbiting stars closer to us. The

flagship mission to carry forward the search for

Earth-like worlds will be the Terrestrial Planet

Finder (TPF), which will image nearby planetary

systems and separate out the extremely faint light

of a terrestrial planet from its parent star. It will be

difficult to see Earth-like planets, because they are

even fainter than their giant planet siblings and

because they must orbit much closer to the glare

of their parent stars for life-giving liquid water to

exist. Daunting as this may be, TPF’s goal is to do

just that, to find Earth-like worlds orbiting any

one of about 150 nearby stars.

Once we have found terrestrial planets orbiting

nearby stars, we can then tackle two even more

ambitious objectives: first, to determine which of

these planets actually have conditions suitable for

life, and second to find which, if any, among those

actually show signs of past or present life. Studies

are already under way to learn which “biosignatures”

—identifiable features in the spectrum of the

planet’s light—can reveal past or present life on a

planet, and to plan future telescopes capable of

making such observations.

Toward the ultimate goal of finding life on

other Earths, Origins will address a sequence of

questions:

• What are the properties of giant planets orbiting

other stars?

• How common are terrestrial planets? What

are their properties? Which of them might be

habitable?

• Is there life on planets outside the solar system?

O B J E C T I V E T H R E E

23
24

Future Researchers Prepare for NASA Missions

An excited hum of voices fills

the Phillips Auditorium at the

Harvard Smithsonian Center for

Astrophysics in Cambridge,

Massachusetts. It is Tuesday,

June 25, 2002. Sixty-five students and young researchers

from around

the country are

huddled over

laptop computers trying

to make sense

of sample

data from the

Palomar Testbed Interferometer. It is the second day

of a weeklong summer school

on the practical application

of optical interferometry in

astronomy.

This year, the summer school

runs for the fourth time as part

of the Michelson Fellowship

Program to encourage and

support the next generation

of researchers in becoming

familiar with interferometry, a

powerful technique considered

for a series of NASA missions.

O B J E C T I V E T H R E E

The program is sponsored

by NASA’s Navigator Program

and also offers fellowships for

graduate students and postdoctoral scholars.

One of the 21 instructors of

the week is Dr. Michelle CreechEakman, a researcher on the

team that took the original data

the people at the laptops are

discussing. Dr. Creech-Eakman

and Dr. Peter Lawson, the organizer of the scientific program

24

of this and the preceding

summer schools, are two

examples of how experienced

researchers can inspire their

future colleagues in sharing

their expertise and using

their numerous contacts with

colleagues in the field. They

are looking forward to meeting some of today’s students

in the years to come as collaborators on some of the

missions currently on the

drawing board.
25

Research Area Five

What are the properties of giants orbiting other stars?

Our solar system contains both distant gas-giant

planets (notably Jupiter, Saturn) and much smaller

terrestrial (rocky) planets in or close to the Sun’s

habitable zone—Venus, Earth, and Mars. Studies

of planet-induced velocity “wobbles” of other stars

have already found more than 100 giant planets,

some in near-circular orbits as far from their parent

stars as Jupiter is from our Sun. These few are quite

reminiscent of our own solar system. Although we

cannot with this method detect terrestrial planets

in these systems, we can learn a great deal about the

degree to which they resemble our own solar system

by studying the giant planets themselves. Also, by

perfecting new observational tools to study the

properties of these giant planets we will take a big

step toward developing the more advanced tools

that will later be required for finding and studying

terrestrial planets.

A first characterization of the properties of one

giant planet has already been achieved, by careful

study of the combined light of the planet and its

parent star. This would normally be extremely difficult because a planet’s light is typically between a

million and a billion times fainter than its star and

the planet is so close to the star that its faint light is

lost in the star’s glare. This first characterization was

possible because the orbit of the planet just happens

to be aligned so that the planet passes directly in

front of the star during its orbital path. The exact

amount of the starlight the planet blocks tells the

size of the planet, which, interestingly, is about the

same as our own Jupiter. A tiny fraction of the star’s

light is absorbed by the planet’s atmosphere while

it transits the star; detailed analysis of its spectrum

tells us something about the chemical composition

of the planet’s atmosphere, and even about the

possible presence of opaque clouds high in the

atmosphere. These observations require extraordinary precision—best attainable only from space

by large telescopes such as the Hubble Space

Telescope (HST) or the James Webb Space Telescope ( JWST), or possibly by giant ground-based

telescopes equipped with large spectrographs.

Future observations of this sort may even reveal

circulation patterns in the giant planet’s atmosphere, and day/night side variations.

If we are lucky, we may discover more such transiting giant planets passing in front of their stars.

But a more powerful tool for understanding the

properties of giant planets requires the development

of instruments that can actually make an image of

the planetary system, so that the light of planets is

separated from that of the parent star. Though difficult, direct imaging of giant planets has powerful

diagnostic potential, by enabling the direct observation of orbital motions, measuring planetary rotation

and seasonal effects, and undertaking detailed studies of the composition of their atmospheres. Direct

imaging of the giant planets in extrasolar planetary

systems will mark a major milestone in our search to

understand the nature and origins of our own solar

system. The techniques developed in the process will

lay the foundation for a later generation of instruments with the greater sensitivity necessary to image

terrestrial planets and to search for signs of life.

Research aimed toward understanding the physical properties of giant extrasolar planets incorporates

two investigations:

• Study the properties of giant extrasolar planets

using the combined light of the planet and the

parent star.

• Detect giant planets by direct imaging, and study

their properties.

O B J E C T I V E T H R E E
26

O B J E C T I V E T H R E E

Detection of the faint

light from an Earthlike planet in the

glare of its parent

star. Instruments are

being studied which

will suppress most

of the starlight and

will provide lowresolution spectra

of the planet.

INVESTIGATION 11

Study the properties of giant extrasolar planets

using the combined light of planet and parent star.

The information derived from the one transiting planet

presently known suggests that observations of others will

become increasingly valuable in coming years—extensive

ground-based surveys are beginning that should detect

many more. Follow-up studies using both space telescopes

(e.g., JWST) and large ground-based telescopes can then

yield detailed information of the sort described above.

Most extrasolar planets, of course, do not have orbits

fortuitously tilted so that they transit directly in front of

their stars. But even for non-transiting planets we may

tease some information about the composition of their

atmospheres from the combined light of star and planet.

Specialized techniques at very large ground-based telescopes (for example differential phase interferometry, and

Doppler deconvolution) may reveal some atmospheric

constituents of giant planets close to their parent star. And

from space, the Kepler mission and others like it can measure the tiny change of the system’s total brightness as the

planet orbits from “new moon” phase to “full moon” phase.

Information gleaned in this way from the combined light

of planet and star, together with theoretical analysis, will

tell us a great deal about the atmospheres and interiors

of giant planets. For example, the combination of observations and theory may help us determine whether the

central cores of giant planets are made up of heavy

“rocky” elements or lighter gases. Calculations of atmospheric circulation and winds in strongly heated close-in

giant planets may be tested by high-precision observations from Kepler or other spacecraft through measurements of how much the light and heat emitted toward

Earth from such a planet varies over its orbit.

INVESTIGATION 12

Detect giant planets by direct imaging, and study

their properties.

While much can be learned by studying the combined

light from a star and its planets, the ability to make an

image of the system, and thereby separate the planet’s

light from that of the central star, will open up far greater

opportunities. Making such an image is a significant technical challenge, even for giant planets that, like our own

Jupiter, are relatively bright because of their huge size and

also lie relatively far (several astronomical units) from their

parent stars. Nevertheless, telescopes and instruments are

now being developed to provide the huge dynamic range

12

10

8

6

4

2

0

–2

log λNλ photons m–2s–1

1 10

λ, μm

Sun

O2 Earth

O2

H2O

CO2

7 17

>106
27

necessary to separate the faint light of an orbiting planet

from its parent star. Such a capability will enable us to

follow the planet in its orbit, and, together with radial

velocity measurements, determine the mass of the planet

directly. Furthermore, the relative brightness of the planet

and star will give information on its size and reflectivity.

Near- or mid-infrared spectra, even at low spectral resolution (R ~ 20–50) will yield the abundance of key chemical

species like water, methane or ammonia in giant planet

atmospheres. The time variation of the planet’s brightness

will tell us its rotation period. The variation of brightness

and polarization with phase angle can provide information about atmospheric composition and clouds—this is

in fact how the clouds on Venus were first identified and

characterized. Higher-resolution spectra will yield information on the winds and circulation patterns of its

atmosphere.

Ground-based interferometers, for example, the Keck

Interferometer (KI) and the Large Binocular Telescope

Interferometer (LBTI), will make early attempts to separate

faint planetary light from the host star. Although groundbased observations are hampered by the smearing effects

of Earth’s atmosphere, rapidly maturing adaptive optics

systems can correct for much of the damage due to the

atmosphere. Beyond that, nulling interferometry (in which

two or more widely-spaced telescopes work in tandem to

null out most of the light from the star while leaving the

planet’s light undiminished) holds great promise. These

techniques will be vigorously pursued during the next

5–10 years.

Taking such techniques to space avoids the smearing

of Earth’s atmosphere. A moderate-sized telescope in

space could do the job, if equipped with one or more of

several promising technologies. Examples are coronagraphic techniques, which directly block most of the light

from the central star; adaptive optics, which correct for

the miniscule imperfections and flexures of even the most

perfect mirror in space, and shaped or apodized apertures, which minimize the starlight diffracted into certain

parts of the image. A complementary approach is nulling

interferometry in the mid-infrared, which will detect the

heat radiated by a giant planet rather than its reflected

light. Infrared observations must contend with the bright

infrared emission from zodiacal dust surrounding the star

(as well as the emission from the dust that surrounds our

own Sun). However, infrared observations have an advantage because the planet’s infrared radiation will be only

O B J E C T I V E T H R E E

Mars Global

Surveyor looks

back at Earth.

This would be the

spectrum of an

extrasolar planet

which is truly

Earth-like.

0 5 10 15 20 25 30

Intensity

Wavelength (μm)

Water

Carbon Dioxide

Ozone

10

9

8

7

6

5

4

3

2

1

0

Water
28

about a million times fainter the parent star’s, rather than

a billion times fainter as is the case for reflected light.

NASA is studying several such approaches that

would allow study of a planet’s light separated from that

of its parent star and hence direct characterization of

the planet’s properties. These approaches include both

coronagraphic and interferometric techniques. While

studying these approaches will ultimately lead to an

advanced mission—the Terrestrial Planet Finder—to

image much smaller Earth-sized planets, they also are

applicable to the easier problem of imaging giant

planets. Indeed, the time is at hand for a mid-sized space

mission to apply such an approach to imaging giant

planets. Such a mission, carried out during the present

decade, would lead to a major near-term advance in

understanding the nature of gas-giants, including the

formation and evolution of these planets and of the

planetary systems in which they occur. At the same time

such a mission will help solidify the technical base for

pursuing the next, eagerly anticipated step of searching

for the rocky terrestrial planets that could harbor life.

O B J E C T I V E T H R E E
29

Research Area Six

How common are terrestrial planets? What are their

properties? Which of them might be habitable?

Extrapolating from our own solar system, the most

reasonable home for life elsewhere in the universe

is a terrestrial planet (or rocky satellite of a giant

planet) that lies within its star’s “habitable zone”

(HZ), so that liquid water can flow on its surface.

Such planets will of course be much harder to

detect than the Jupiter-like planets, because of

their small size and relative closeness to their

parent star.

For terrestrial planets, just as has been the case

for giant planets, observations of transits will give

us important early information. As noted in Chapter 2, the Kepler mission later in this decade will

use transit measurements to answer the question of

whether rocky planets in stellar planetary systems

are common or rare in the extended solar neighborhood (within 200–600 parsecs of the Sun). But

Kepler will detect Earth-like planets through their

very uncommon transits, which means it must

monitor hundreds of thousands of relatively distant

stars to reap a significant number of detections.

While the individual Earth-like planets Kepler will

discover will be too distant for detailed follow-up

study, the frequency of their occurrence will be

crucial for planning later missions that can directly

detect and characterize terrestrial planets orbiting

closer stars.

Another very important precursor mission

will be the Space Interferometry Mission (SIM).

By measuring the astrometric (that is, positional)

wobble of nearby stars, SIM will be able to detect

planets as small as a few Earth masses, in the habitable zone surrounding a number of nearby stars.

The data will also yield the mass of the planet

directly. This will be an important prelude to actual

imaging of terrestrial planets, which will be carried

out by the Terrestrial Planet Finder (TPF) mission.

TPF will use coronagraphic or interferometric

techniques to actually image terrestrial planets

orbiting nearby stars (although each planet will

appear only as a single point of light). This will

yield important information on the physical properties of extrasolar terrestrial planets, including their

size, temperature, and location within the habitable

zone. From our knowledge of the solar system we

can then make a fair estimate of their mass, which

determines how well the planet can retain an atmosphere, and also whether it is likely to have a history

of active volcanism and plate tectonics. All of these

considerations enter into the question whether the

planet is able to support life.

Another important role for the TPF mission

will be to create a census of those terrestrial planets

orbiting nearby stars that appear to meet the basic

requirements for habitability, as determined by their

mass, location with respect to the habitable zone,

properties of the parent star, etc. Such a census will

provide the observing list for the much more intensive studies, carried out first by TPF and perhaps

later by a Life Finder (LF) mission, to actually detect evidence for past or present life on such planets.

Research toward characterizing terrestrial planets and identifying those that might be habitable is

divided into two investigations:

• Which nearby stars host terrestrial planets that

might be suitable for life?

• What are the compositions of the atmospheres

of terrestrial planets orbiting nearby stars? Which

of these planets are suitable abodes for life?

O B J E C T I V E T H R E E
30

150 stars? Unfortunately, we may not know the answer to

this important question until nearly the end of this decade,

when the first data from Kepler and SIM are returned.

However, unless terrestrial planets are rare indeed, TPF

should locate dozens of terrestrial planets in the habitable

zones surrounding those 150 stars.

The exact architecture of the TPF mission is still to be

selected, from among two contending approaches. One is

a coronagraphic telescope, which makes use of large and

very precise optics to obtain images at visual wavelengths

of a planetary system after the brilliant light from the

central star has been blocked out by internal blockers

within the telescope. The other is an infrared interferometer, which combines the light from several moderate sized

telescopes distributed over a long baseline. The telescopes

might all be mounted on a single long boom, or alternatively they might be separated in space and steered relative to each other to maintain their separation to exquisite

accuracy. Either the visual light coronagraph or the infrared interferometer could in principle do the job of detecting terrestrial planets closer than about 15 parsecs, so the

choice will probably come down to technical feasibility

and cost.

Once a planet has been detected, repeat observations

over its “year” will determine its orbital period and distance

from the parent star. This already will give an important

first clue to its temperature, i.e., whether it does indeed lie

O B J E C T I V E T H R E E

Simulation of a

mid-IR image from

a space-based

coronagraphic

telescope of an

Earth-like planet

orbiting a Sun-like

star at a distance

of 8 light-years.

INVESTIGATION 13

Which nearby stars host terrestrial planets that

might be suitable for life?

In order for us to assess the habitability of an extrasolar

terrestrial planet, it must be close enough to us for detailed investigation. Ongoing precise radial velocity surveys are beginning to uncover relatively nearby planetary

systems that are good candidates for having terrestrial

planets in their habitable zones. At the end of this decade

SIM should be able to detect a few terrestrial planets if

they exist in orbit around nearby stars, and measure their

masses. These activities will set the stage for a comprehensive search for terrestrial planets orbiting nearby stars,

to be carried out by TPF.

The goal of TPF is to image nearby solar systems, with

such precision and sensitivity that it can separate out the

light from a rocky planet in orbit within or near the star’s

habitable zone, from the parent star itself. Direct detection of such planets is extremely difficult, both because of

their intrinsic faintness and their closeness to the parent

star. It is expected that TPF, when it is launched sometime

in the next decade, will be able to find terrestrial planets

(if they exist) around any of about 150 stars closer than

about 15 parsecs to Earth. (The nearest star is about

1.3 parsecs from Earth.) How many terrestrial planets

might there be in the habitable zone around those
31

within the star’s habitable zone. Another key characteristic

is the planet’s size, and hence its mass. Even if the planet is

located in a stellar HZ, too small a mass means that any

atmosphere will be quickly lost, whereas too large a mass

could mean an atmosphere so thick so that sunlight does

not reach its surface. Mass also determines the likelihood

of plate tectonics; in turn this may be important in cycling

surface material and hence affecting the conditions conducive for life.

If Earth-like planets are found orbiting the closest stars,

their masses may be determined directly by SIM. Otherwise, planet size can be estimated at least crudely either

from data in the mid-infrared, such as can be obtained by

the infrared interferometer version of TPF, or from the

amount of visible reflected light as can be obtained by the

visual coronagraphic version of TPF. Then, from the planet’s

size, together with knowledge of the relation between

size, mass, and thermal environment of solar system rocky

planets, one can make a reasonable estimate of the

planet’s mass.

INVESTIGATION 14

What are the compositions of the atmospheres of

terrestrial planets orbiting nearby stars? Which of

these planets are suitable abodes for life?

To determine whether a planet is likely to be habitable,

many other properties of the planet must be investigated

in addition to whether the planet lies within or near its

star’s habitable zone. Many of these properties can be

revealed by the spectroscopic capability of TPF, which can

explore the composition of the atmosphere and in some

cases the surface of the planet.

TPF will have sufficient spectroscopic capability (resolution R ~ 20–50) to measure the composition of the atmosphere of the planet. Spectra of this resolution can be used

to detect evidence for gases such as carbon dioxide or

water vapor. The visible and infrared spectrum, in conjunction with theoretical and empirical models, can tell us

about the amount of atmosphere, the gases present in the

atmosphere, the presence of clouds, the degree and variability of cloud cover or airborne dust, and the presence of

a greenhouse effect. The concentration of greenhouse

gases can determine whether the surface is warm enough

to maintain liquid water, even if (as for Earth) the equilibrium temperature without such gases would result in a

frozen surface. Clouds and dust aerosols can determine

the amount of light absorbed and reflected, and thus the

surface temperature. Spectra can also tell us about the

surface, whether it is rock-like with little or no overlying

atmosphere, or whether it has strong surface biosignatures, such as the red-edge spectral feature of photosynthesizing vegetation on Earth.

The issue of habitability also involves the properties

of the planetary system, including the star itself. A shield

of outer giant planets, their presence gleaned from the

missions discussed earlier, may be a crucial ingredient for

protecting a terrestrial planet from bombardment from

outlying belts of comets and asteroids. Conversely the

presence of asteroids and comets, at least early in the

O B J E C T I V E T H R E E

Planets cause the

apparent position of a

star to wobble. Viewed

from a distance of

30 light-years, our Sun

would move by its own

diameter (yellow circle),

due mainly to the pull

of Jupiter and Saturn.

2000

1995

2010

1990

2015 2005

0.001”

0.001”

2020
32

history of the stellar system, may be important if these are

the delivery vehicles for water and complex organics to an

inner terrestrial planet, as may have been the case during

the early evolution of Earth. As for the star itself, what must

its age be so that life might reasonably be expected to have

arisen by now, given what we know of the evolution of life

on Earth? How low must its early magnetic activity level

have been to allow life to evolve without damage by highenergy radiation from stellar flares? Does it matter if the

galactic orbit of the star has carried the system out of the

galactic plane or through regions of strong star formation

(and hence strong UV flux), also exposing any nascent life

to unhealthy radiation environments? What other hazards

to habitability are there? These questions are appropriate

for Earth-based telescopes and will require a continuing,

vigorous research and analysis program for understanding

the varied and complex data.

O B J E C T I V E T H R E E

TPF will make at least several observations of each star

which is a candidate for hosting a terrestrial planet. If a

terrestrial planet is found in or close to the star’s habitable zone, the mission will make intensive observations

of the system, not only to verify the discovery but also to

explore the planet’s spectrum in detail, including its time

variability. The latter will give information on the diurnal

rotation period, and also seasonal variations of the atmosphere and surface, as well as on the presence of transient clouds and dust aerosols.

TPF will thus not only find terrestrial planets around

nearby stars, but will also explore their suitability for

hosting life. This work will phase directly into the next

and most exciting step in the Roadmap—the search for

actual signs of present or past life on the most promising

candidates.
33

Is there life on planets outside the solar system?

Research Area Seven

The ultimate goal of the Origins program is of

course not just to discover which extrasolar planets

might be conducive for life, but rather to detect

actual evidence for life on one or more of those

planets, in order to answer the age-old question,

“Are we alone?”

The search for life on extrasolar planets is

founded upon the premise that signatures of life

(biosignatures) in astronomical observations will

be recognizable. We already know from observations of our own planet that surface biosignatures

could be detected. Potential biosignatures include

the characteristic spectra of life-related compounds

like oxygen and water vapor, but care must be

taken because they are not uniquely signs of the

existence of life. It is very important to explore

possible biosignatures in great detail, both theoretically and in the laboratory, so as to identify the

key spectroscopic capabilities that TPF must have,

and the extent to which observations are required

at optical wavelengths, infrared wavelengths, or

both. These findings will be a very significant

determinant in shaping the architecture of the

TPF mission.

While it would be very exciting to discover a

near-twin of Earth orbiting a close-by star, and

then study it carefully for signs of life, we should

cast a broader net. For example, a planet as remote

from its star as Mars is from the Sun, if it is massive enough to retain a “greenhouse” atmosphere,

may be warm enough and wet enough to sustain

life at its surface. The key requirement that a

planet have a surface temperature permitting

liquid water depends on many factors beyond

its mean distance from its star, including its

reflectivity and the composition of its atmosphere, which determines the extent of greenhouse warming and hence the planet’s surface

temperature. In addition, it is important to

determine the temperature difference between

the “day” side and “night” side of the planet, for

example through infrared observations of the

planet at different portions of its orbit, and

optical observations of the diurnal change in

its optical reflectivity.

After TPF is developed and deployed, it will

use its capabilities not only to make a first reconnaissance of the nearby terrestrial planets, but

also to go further and study in detail those planets which have the greatest likelihood for habitability—searching for the tell-tale biosignatures

uniquely indicating the existence of present or

past life on those planets. This search will not

be easy, and may well require a larger and more

advanced follow-on Life Finder mission using

technologies yet to be defined.

To make progress in this challenging research

area, we must proceed in two steps:

• Determine the optimal biosignatures for life on

other worlds.

• Search for these biosignatures as evidence of

life on habitable planets orbiting other stars.

O B J E C T I V E T H R E E
34

INVESTIGATION 15

Determine optimal biosignatures for life on other

worlds.

An astronomical biosignature is a spectral, photometric

or temporal signal whose origin specifically requires a

biological agent. To find past or present life beyond the

solar system, we must identify robust biosignatures and

learn how to measure them on extrasolar terrestrial planets. Planets can create non-biological features that mimic

biosignatures, and these must be thoroughly understood

to avoid false detections. At the same time our compilation of biosignatures and non-biological imitations must

embrace a broad diversity of possible biota and habitable

O B J E C T I V E T H R E E

Methane-producing

bacteria could have a

profound effect on the

atmosphere of the early

Earth, producing strong

absorption in the midinfrared at a wave

number of 1300 cm-1

(7.6 micrometers).

conditions in the universe, probably exceeding the diversity of such features on Earth. Having determined the best

signatures of life on other worlds, we must then use them

to detect present or past life on planets orbiting nearby

stars.

An important biosignature is oxygen. In Earth’s atmosphere, oxygenis produced during photosynthesis, the

process by which green plants use sunlight to convert

carbon dioxide and water into carbohydrates. Once created, molecular oxygen may combine with other molecules in the process of oxidation, and thus disappear as

a spectral signature unless it is continually replenished

by further photosynthesis. Thus a significant presence of

oxygen, as well as water vapor and carbon dioxide, would

Wavenumber (cm–1)

400 600 800 1000 1200 1400

0.0e+00

5.0e–06

1.0e–05

Radiance (W/(cm2 sr cm–1))

H2O

CO2

CO2

CO2

H2O

no CH4

Prebiotic Earth

CH4

1% CH4

Wavenumber (cm–1)

400 600 800 1000 1200 1400
35

suggest that life is present. Molecular oxygen is detectable in the red part of the visual spectrum, and its photolytic product ozone is detectable in both the visible and

infrared. The search for biosignatures of oxygen or ozone

is a key part of the TPF mission.

A potential biosignature is methane, which is produced by life but also has many non-biological sources.

Another biosignature is nitrous oxide, which is produced

only by biological sources. Unfortunately, these gases are

not very abundant in the Earth’s atmosphere—their spectral signatures are weak—so their detection on another

Earth-like planet will probably require a later-generation

successor to TPF, such as Life Finder.

To identify the key biosignatures, both field and laboratory observations as well as theoretical simulations

must be conducted in order to examine the relationships

between the structure and function of microbial ecosystems and the gaseous products they produce. Ecosystems

that are analogs of our ancient biosphere (e.g., based

upon chemosynthesis or upon non-oxygen-producing

photosynthesis, in heat-loving and subsurface communities, etc.) should be included. The effects of key environmental parameters such as temperature and abundance

of H2

, CO2 and O2 should be evaluated, because these

parameters probably varied during planetary evolution.

Ecological processes that have been affected by oxygenproducing photosynthesis are centrally important, not

only because they determine the net flux of oxygen (a key

biosignature) to the atmosphere, but also because photosynthesis potentially sustains high rates of production of

other biosignature gases, including reduced species.

Habitable planets are geologically active and therefore

can create non-biological features that mimic biosignatures. For example, hydrothermal processes on a planet

that exhibits a more reduced crustal composition than

that of Earth might produce methane at rates comparable

to biological rates on Earth. To cite another example, nonbiological processes of oxygen production might be able

to sustain detectable levels of atmospheric oxygen on a

planet that is less geologically active than Earth. Accordingly, it is imperative to characterize the environmental

conditions of any planet for which potential biosignatures

have been identified.

O B J E C T I V E T H R E E

Biosignatures in atmospheres and surfaces can be

altered chemically by photochemical and other reactions

that occur in atmospheric gases and also in clouds in the

lower atmosphere. These species can also be transported to

the upper atmosphere and encounter additional reactions.

Which biosignatures survive these atmospheric processes?

In what chemical form do they survive? How does their

survival and/or transformation vary as a function of atmospheric vertical structure, composition, temperature, circulation and cloud content? Both laboratory and theoretical

simulations are required to investigate atmospheres of

habitable planets that differ from our own modern atmosphere. Examples include atmospheres that lack O2

 and/or

include clouds of varying composition, including compositions that occur near the limits of habitable zones (e.g.,

dense H2

O clouds, CO2 clouds) or on a young planet.

Based on our knowledge of the history of life on Earth,

we can expect that the spectral signatures of life on other

planets will depend significantly on the age of the planet.

NASA’s astrobiology research will help expand our knowledge of how these signs of life would appear at various

stages in the planet’s history, including for a planet whose

properties and history are not exactly the same as our own.

Research on understanding the optimum spectral signatures of life is urgent, and already well under way. The results

of this research will be key in determining the design of

TPF and its Life Finder successor, for example to what extent

it stresses optical spectroscopy (which may be possible

using coronagraphic techniques) or infrared spectroscopy

(which may require an interferometer with widely separated

apertures).

INVESTIGATION 16

Search for evidence of life on habitable planets

orbiting other stars.

The knowledge of which spectral features are unambiguous

indicators of the presence of life on a planet, and which of

those are technologically the easiest to measure, will be very

important for the final design of TPF. According to present

plans, TPF should have enough spectroscopic capability to
36

O B J E C T I V E T H R E E

The development of life on

the early Earth

provides clues

to the possible

evolution of

life elsewhere

search for the more abundant atmospheric species that

would indicate life on those planets. A current plan calls

for finding and studying those terrestrial planets that

may orbit any of about 150 Sun-like stars within about

15 parsecs of the Sun. However, the size of the search

space will be refined as we learn more about how rare

or common terrestrial planets really are orbiting other

stars—for example, from the Kepler mission. While detecting even one life-bearing planet in orbit around another

star would be a tremendous milestone, the converse—

learning of the absence or near-absence of life on other

worlds, would require a large number of examples to draw

a statistically meaningful conclusion. The distance to

which one must search to find that number of examples,

and hence the limits on apparent brightness of the planet

and its angular separation from the parent star, will become well determined only over the next half decade.

Already it can be guessed, however, that unless planets

showing very robust signatures of life are very common

orbiting Sun-like stars, the search will ultimately require

the most advanced tools we can marshal, probably going

beyond the capabilities of the TPF mission as it is presently conceived. Conceptual studies are already beginning to define a follow-on Life Finder mission dedicated

to this goal. With greater collecting area offering greater

spectral resolution, Life Finder will make possible the

search for additional biosignatures, especially those

gases that have unambiguously out-of-equilibrium

abundance—incontrovertible evidence for life. Life

Finder would also provide greater spatial resolution that,

together with its greater light grasp, would allow us to

extend our search for Earth-like worlds beyond the limits

of our first exploration with TPF to perhaps thousands of
37

O B J E C T I V E T H R E E

stars. The dual goals of extending our search to further

planetary systems and providing greater, time-resolved,

spectral information will challenge our imagination and

technical prowess for decades to come.

Ultimately, and beyond the scope of this roadmap, lies

the question of whether there is life in the wider universe,

for example on planets orbiting stars so far away that

there can be no hope of detecting life by studying biosignatures in the spectra of those planets. We can only

extrapolate outward, from our knowledge of life in the

solar system and around relatively nearby stars, to ascertain the likelihood of life throughout our galaxy, or our

sister Andromeda Galaxy, or even beyond out into the

distant universe. If life is found anywhere within our stellar

“neighborhood,” then we can conclude it to be highly

probable that life is common in our galaxy, and surely so

in the wider universe. Conversely, if present or past life is

found to be absent from our stellar neighborhood except

for here at home, then this information surely will inform

our view of how rare life is anywhere in the universe, and

how precious it is on Earth.
4 OriginsMissions and Tools

Keyhole Nebula

as seen from the

ground in the

near-infrared.

The nebula is a

breeding ground

for some of the

hottest and most

massive stars

known, each

about 10 times

as hot and 100

times as hefty as

the Sun. Image:

NASA/2MASS

CHAPTER
39

...to build on the past, and leave

a legacy for future missions.

The central principle of the Origins mission architecture has been that each major mission builds on the

scientific and technological legacy of previous missions, while providing new capabilities for the future. In

this way, the complex challenges of the theme can be achieved with reasonable cost and acceptable risk.

For example, the techniques of interferometry developed for the Keck Interferometer, the Large Binocular

Telescope Interferometer and the Space Interferometry Mission, along with the infrared detector technology

from the Space Infrared Telescope Facility and the large optics technology needed for the James Webb Space

Telescope will enable the Terrestrial Planet Finder to search out and characterize habitable planets.

M I S S I O N S A N D T O O L S

Inspired by bold vision, this philosophy has allowed

the Origins theme to navigate through many daunting scientific and technological questions, toward a

set of specific scientific missions, and toward scientific goals that stretch even beyond the missions we

now know how to define. Six years down the path

from the first Origins Roadmap, much has been

learned about the technological difficulty and the

scientific framework for this scientific theme, which

brings into play another feature of a robust strategic

plan: flexibility and adaptability. Origins has a

policy of ensuring that all major technological problems have been solved prior to embarking on the

expensive construction phase of its challenging

missions. Even so, the challenges to achieving the

scientific goals of Origins are so great, that in addition to mission-oriented enabling technology developments, additional options for gaining precursor

scientific knowledge through observations from the

ground, work in scientific theory, and more modest

precursor missions must be added to the future

investigative agenda. While the vision remains, the

path and the pace must be what the nation will

afford.

At the publication of the Origins 2000 Roadmap,

less than half the extrasolar planets now known had

been discovered. Today, we see increasing pace of

discovery through ground observations of radial

velocity Doppler shifts and photometric transits as

data sets are filled in. Technology development and

mission architecture studies conducted in the previous decade did not suggest that large single-aperture visible-light coronagraphs would be viable for a

terrestrial planet finding mission. Today, Terrestrial

Planet Finder (TPF) architecture studies and technology development do include coronagraphs, and

also precursor mission options of reduced scope.

The recently selected Kepler mission in the Discovery Program will provide valuable planetary system

statistics, and exemplifies the kind of alternate approaches Origins must embrace. The dynamic state

of this emergent scientific field suggests strongly

that the program undertaken to achieve the Origins

goals must remain flexible, and must adapt to and

make use of evolving technical and scientific knowledge and capability. The Origins roadmap for 2003

elaborates on the previous plan, adding “off-ramps”

from some endeavors that may prove too difficult

39
40

A few hundred participants

and their families gathered in

May 2002 at Pasadena City

College to learn about Origins

science and celebrate the winners of the “Imagine a New

World” art and essay contests, sponsored by Girls

Inc. and NASA’s Navigator

Program.

Girls Inspired to Imagine New Worlds

M I S S I O N S A N D T O O L S

40

Taking an interdisciplinary

approach, the contests were

provided through the Operation SMART program, an

age-appropriate curriculum

that builds girls’ skills in

math, science, and technology. Co-sponsor Girls Inc. is

a national nonprofit youth

organization dedicated to

inspiring all girls to be

strong, smart, and bold.

Elementary and middle

school-age girls in the Los

Angeles area were asked to

imagine life on a distant

planet, using Navigator educational materials as background. A diverse panel of

judges graded the entries

based on creativity, literacy,

and incorporation of Navigator themes.

The contest was capped off

with a celebration at which

the winners were presented

with awards and certificates.

All participants were treated

to a half-day of fun learning

activities, including “Ask a

Scientist,” “Taking the Measure of the Universe,” and

planetarium tours.
41

M I S S I O N S A N D T O O L S

or too costly to maintain, and finding “alternate

routes” to arrive at the same objectives, while reflecting realistic assessments of the cost and risk

inherent in scientific discovery and exploration.

Origins will solicit new ideas for technology

developments and scientific missions of moderate

scale that hold promise for facilitating the Origins

goals. Solicitations through NASA Research Announcements will provide a science and technology

incubator to obtain and support proposals for technology development and mission concept definition

studies. The most promising of these may be

pursued as possible flight missions through the

Explorer or Discovery Programs or even a future

competed mid-size Origins mission program.

Complementing the missions described below, the

Research and Analysis (R&A) program provides

three essential components of the Origins theme:

(1) development of key technologies that will be

necessary for Origins missions; (2) development

of alternate mission concepts which could lead to

smaller-scale intermediate missions exploring

aspects of the Origins scientific agenda; and (3) a

broad program of scientific theory and analysis

that helps frame the scientific questions, provides

models to define the science requirements for key

missions, and is critical for the understanding of the

vast amounts of data expected from space missions

in the coming decade. Increasingly, the development of strategic missions will invoke, and fund,

targeted application of R&A programs to help draw

in a broad constituency in developing new scientific

knowledge and technology. The Origins R&A

program is described in Chapter 6.

Even as we work to develop the missions for this

and the next decade, we must start now to envision

where our explorations will lead us afterwards, as

developing the needed technologies can easily

take a decade or more before they are ready to be

applied. Our focus will be placed not on specific

missions, but on the compelling scientific questions

and the technologies that will enable the missions

and tools to find the answers. Beyond TPF, scientific attention will turn to detailed studies of any

indications of life found on the planets that TPF

discovers. This will require a still more capable

spectroscopic mission, a Life Finder (LF), which

will probe the infrared spectrum with great sensitivity and resolution. Both Origins and the Structure

and Evolution of the Universe Theme call for

advanced investigations in galaxy and planetary

system formation and cosmology that require a high

resolution IR telescope such as the Single Aperture

Far-Infrared Observatory (SAFIR), an 8-meter

space-based telescope recommended in the National Research Council decadal survey. Such a

telescope might launch and operate between TPF

and LF to carry out its own science program, and to

lead to the 25-meter telescopes needed for LF. The

technology developed for such a mission might also

be used as a building block for a kilometer-baseline

interferometer used at far-infrared wavelengths for

cosmological studies. Investigations in distribution

of matter in the universe (including dark matter)

will require a large-scale UV/optical observatory

that will build on the technology developments of

the James Webb Space Telescope ( JWST) and of

the Space Interferometry Mission (SIM), and pave

the way for more challenging UV/optical telescopes

of the future. The technology developments necessary to enable these missions are described in

Chapter 5, Enabling Technologies.

While the Astronomical Search for Origins and

Planetary Systems remains inspired by a far reaching vision, the rules of the road will be those of

clearly focused waypoints and sound management

practices.

Operational Missions

Foremost among the current Origins missions is

the Hubble Space Telescope (HST), which was

launched in April 1990, and—thanks to regular upgrades of its instruments via Shuttle servicing missions—remains NASA’s most productive scientific

program. This impressive record of achievement

continued into the second decade of HST’s
42

M I S S I O N S A N D T O O L S

operation, with the installation in early 2002 of

the Advanced Camera for Surveys (ACS) and a

new active cooling system to reactivate the Near

Infrared Camera and Multi-Object Spectrometer

(NICMOS). The subsequent and probably final

Shuttle servicing mission, planned for 2004, will install both the highest performance ultraviolet spectrograph ever flown in space, the Cosmic Origins

Spectrograph (COS), as well as the first truly panchromatic imaging system ever flown in space, the

Wide-Field Camera 3 (WFC 3). This mission will

also install a number of engineering system replacements to enable the observatory to operate through

2010, at which time it is planned to retrieve the

telescope in the Space Shuttle.

The importance of HST to the scientific community is matched by the positive role that the

mission has played in educating the public about

science. The observatory may be the best-known

scientific facility in the world, with its results used

in classrooms globally.

The most recent Origins mission to be launched

is the Far-Ultraviolet Spectroscopic Explorer

(FUSE), which explores the universe at wavelengths that are inaccessible by HST. In particular,

FUSE is determining the abundance of deuterium,

an isotope of hydrogen that was formed in the Big

Bang. Determination of its abundance is essential to

constraining conditions in the Big Bang. Beyond

this, FUSE will also investigate the hot interstellar

gas, in order to understand the life cycle of matter

between the stars, as gas cycles between stellar

death and rebirth. A highlight of the education and

public outreach program of the FUSE mission is its

highly visible role in the Maryland Science Center,

in Baltimore, which is visited by over 600,000 persons per year.

Ground Observatories

The Origins theme supports a broad science program in conjunction with the W.M. Keck Observatory in Hawaii. This program has two main thrust

areas: first the sponsorship of community-accessible

time on single Keck telescopes to pursue Origins

science goals; and second, the development and

operations of the Keck Interferometer (KI). The

single-Keck program has been in place since 1996,

and has been extremely successful in producing

important scientific results such as radial velocity

exo-planet detections, spectral characterizations of

L and T-dwarfs, and mid-infrared imaging of planetary debris disks. KI has combined the infrared

light collected by the two 10-meter Keck telescopes

to undertake a variety of Origins astrophysical investigations. Among the issues addressed by KI

will be the location and amount of zodiacal dust in

other planetary systems and the astrometric detection and characterization of exo-planetary systems

around stars in the solar neighborhood. This first

in-depth and long-term census of planets will be an

important contribution to our understanding of the

architecture and evolution of planetary systems, and

will be key in helping to define the requirements

and the architecture for TPF.

The Large Binocular Telescope Interferometer

(LBTI) will further a variety of Origins goals in

The Space Infrared

Telescope Facility

will contribute

extensively to the

understanding of

the formation of

stars and planets

and will investigate

the formation and

early evolution of

galaxies.
43

M I S S I O N S A N D T O O L S

star, planet, and galaxy formation through both

nulling and wide-field imaging interferometry.

Primary among these goals is a planned systematic

survey of nearby stars to understand the prevalence

of zodiacal dust and gas giant planets and to determine a system’s suitability for terrestrial planets.

The modest baseline and common mount design of

the dual 8.4-meter LBTI allows uniquely sensitive

infrared observations of candidate planetary systems

through nulling interferometry. The development

of nulling technology and observing techniques will

help create a mature technological basis for a TPF

mission. The LBTI also allows wide-field, highresolution imaging of objects down to brightness

levels similar to filled aperture telescopes. This is

applicable to a wide variety of Origins-related

imaging and astrometric observations.

The National Virtual Observatory (NVO) will

build on developments in computing and information technology and will have a major impact on

Origins missions and science. For the most part,

essential technologies will emerge from academia

and industry and will be usable without Originsspecific development initiatives. The NVO will

federate digital sky surveys, observatory and mission

archives, and astronomy data and literature services,

and provide a framework that will reduce the cost of

developing and maintaining future archives and data

services. The NVO will be able to address

research topics of particular relevance to the Origins

program, such as:

• Star formation rates in galaxies

• The environments of clusters of galaxies, e.g,

through systematic searches for gravitational

lenses

• The galaxy merger rate as a function of lookback time

• The population of brown dwarfs, through

cross-correlation of survey catalogs

• Cosmological models, through confrontation

of simulations with observations

• A complete census of Kuiper-Belt objects, and

a compositional atlas of the solar system, as a

means to understanding the formation process

and dynamics of the solar system

The NVO will also be an unprecedented venue

for science and technology education and public

outreach.

Missions Targeted for Operation by 2005

The Space Infrared Telescope Facility (SIRTF)

will be the fourth of NASA’s Great Observatories

and will use imaging and spectroscopy at infrared

wavelengths from 3–180 micrometers to investigate Origins scientific goals. In particular, SIRTF

The Stratospheric

Observatory for Infrared

Astronomy, flying on a

modified Boeing 747

aircraft, will study sites of

star formation, the cold

interstellar medium, and

the center of our galaxy at

high spatial resolution.
44

M I S S I O N S A N D T O O L S

and reducing risk of new instrument technologies,

particularly detectors for future missions such as

SAFIR. It will have a prominent education and

public outreach program, including involving high

school teachers and students in its flights and

observations. SOFIA will be making observations

by 2005.

Missions Targeted to Enter Development

Phase in 2005–2010

Extrasolar planets are a reality: more than one hundred planet-sized objects have been indirectly detected around neighboring stars and their number

is growing rapidly. But the techniques available from

the ground today are capable of detecting only the

most massive such objects, perhaps a few times the

mass of Saturn. The Keck Interferometer will push

this mass limit significantly lower, possibly to the

mass of Neptune. However, it will require spacebased techniques to detect objects that approach the

mass of Earth and allow the first in-depth search

for objects in space like our own home planet.

Kepler is a new mission in the Origins firmament, selected through the Discovery Program and

scheduled for launch in 2007. This provides an excellent example of the kind of moderate scale missions that can contribute to Origins in important

ways. The Kepler mission is specifically designed

to photometrically survey the extended solar neighborhood to detect and characterize hundreds of

terrestrial and larger planets in or near the habitable

zone and provide fundamental progress in our

understanding of planetary systems. The results

will yield a broad understanding of planetary formation, the frequency of formation, the structure

of individual planetary systems, and the generic

characteristics of stars with terrestrial planets.

These results will be instrumental in determining

how deep TPF will have to look to find an adequate

sample of planetary systems to find and characterize

habitable planets.

The Space Interferometry Mission will be the

first observatory capable of detecting and measuring

will contribute extensively to the understanding of

the formation of stars and planets and will investigate the formation and early evolution of galaxies.

SIRTF will provide key information on the dust

environments TPF will need to penetrate to find

and characterize planets. A very important component of SIRTF science will be the Legacy Programs,

in which very large and scientifically important data

sets will be made available rapidly to the entire scientific community. Six teams with broad community

participation have been competitively selected to

execute Legacy Programs. SIRTF is a cryogenic

mission with an expected cryogenic lifetime of up

to 5 years. The wide applicability of infrared technology is highlighted in the mission’s extensive

eduction and public outreach program.

The Stratospheric Observatory for Infrared

Astronomy (SOFIA) will study sites of star formation, the cold interstellar medium, and the center of

our galaxy at high spatial resolution at far-infrared

wavelengths. It is a joint U.S. (80%) and German

(20%) observatory which consists of a 747 aircraft

with a telescope as large as HST. SOFIA will also

function as a unique platform for developing, testing,

The Kepler mission

will complete a

photometric survey

of the extended solar

neighborhood to

detect and characterize hundreds of

terrestrial and larger

planets in or near

the habitable zone.
45

M I S S I O N S A N D T O O L S

the mass of planetary bodies with a few times the

mass of Earth in orbit around nearby stars. Thus,

the Origins theme will take a major step forward in

answering one of its defining questions: “Are we

alone?” Are there other worlds like our own home

planet, existing within planetary systems like our

own solar system? SIM will extend the Keck census

of nearby planetary systems into the range of the

The Space

Interferometry

Mission will extend

the Keck census of

nearby planetary

systems into the

range of rocky,

terrestrial planets.

SIM Technologies

Technology Builds on Leaves legacy for

past missions future missions

Interferometric Keck TPF (interferometer

techniques Interferometer options), Life Finder,

Far-IR Interferometer

Nanometer HST, Chandra TPF, SAFIR, Large UV/Optical

stabilization Telescope, Life Finder

techniques

Picometer New TPF, Life Finder

sensing techniques

JWST Technologies

Technology Builds on Leaves legacy for

past missions future missions

Large, passively SIRTF for passive TPF, Life Finder, Large

cooled optics cooling UV/Optical Telescope, SAFIR

Cryogenic HST-NICMOS, Planck, SAFIR, Life Finder

coolers TPF Technology

IR detectors SIRTF, SOFIA TPF, SAFIR

future missions, including precision location of

optical elements to a fraction of the diameter of a

hydrogen atom (picometers) and the precise, active

control of optical pathlengths to less than a thousandth the diameter of a human hair.

Beyond the detection of planets, SIM’s extraordinary astrometric capabilities will permit determination of accurate positions throughout the Milky

Way Galaxy. This will permit studies of the dynamics and evolution of stars and star clusters in our

galaxy in order to better understand how our galaxy

was formed and how it will evolve. Accurate knowledge of stellar positions within our own galaxy

will allow us to calibrate luminosities of important

stars and cosmological distance indicators enabling

us to improve our understanding of stellar processes

and to measure precise distances throughout the

universe.

The next step beyond the Hubble Space Telescope will be the James Webb Space Telescope,

rocky, terrestrial planets for the first time, permitting scientists to refine their theories of the formation and evolution of planets like Earth. This census

will form the core of the observing programs for

subsequent missions that will investigate in detail

the nature of these newly discovered worlds. It will

provide the “target list” for TPF.

In addition to its scientific goals, SIM will develop key technologies that will be necessary for
46

Kepler

TPF

Coronagraph

Interferometer

Keck

LBTI

SIM

SAFIR

Enabling

Technology

SOFIA

Imager

Large UV/

Optical

Observatory

Life Finder

SIRTF

JWST

Each Origins

mission builds on

the scientific and

technological

legacy of the

previous mission,

while providing

new capabilities

 for the future.
47

M I S S I O N S A N D T O O L S

which will have three times the diameter of HST’s

mirror and about an order of magnitude more lightgathering capability. Because the prime science

goals for JWST are to observe the formation and

early evolution of galaxies, JWST’s greatest sensitivity will be at mid- and near-infrared wavelengths,

where the expansion of the universe causes the light

from very young galaxies to appear most prominently. JWST will be a powerful general-purpose

observatory capable of undertaking important

scientific investigations into a very wide range of

astronomical questions, including those that are

central to the Origins theme.

JWST is expected to have a telescope diameter

of at least 6 meters and be celestial-backgroundlimited between 0.6 and 10 micrometers, with imaging and spectroscopic instruments that will cover

this entire wavelength regime. JWST has a requirement to be diffraction-limited at 2 micrometers.

With these capabilities, JWST will be a particularly

powerful tool for investigating fundamental processes of stellar formation and early evolution, as

well as the later stages of evolution. In both cases,

dust almost completely blocks our ability to observe

the light from rapidly evolving stars, so that detailed observations have to be carried out at longer

wavelengths.

The European Space Agency and the Canadian

Space Agency have agreed to contribute significantly to the JWST project. These contributions

will be important in significantly enhancing the

overall capabilities of the observatory.

Missions Targeted to Enter Development

Phase in 2010–2015

The Terrestrial Planet Finder will directly detect

and study planets outside our solar system from

their formation and development in disks of dust

and gas around newly forming stars to their evolution and even potential suitability as an abode for

life. By combining the high sensitivity of space

telescopes with revolutionary imaging technologies,

TPF will measure the size, temperature, and placement of terrestrial planets as small as Earth in the

habitable zones of distant solar systems as well as

their gas giant companions. In addition, TPF spectroscopic capability will allow atmospheric chemists

and biologists to use the relative amounts of gases

like carbon dioxide, water vapor, ozone and methane to find whether a planet someday could or even

now does support life. Our understanding of the

TPF Technologies

Technology Builds on Leaves legacy

past missions for future missions

Large, passively JWST SAFIR, Life Finder

cooled optics

Formation StarLight LISA, Far-IR Interferometer,

flying ground demo Life Finder

Interferometry SIM, LBTI, Far-IR Interferometer,

and nulling Keck Interferometer Life Finder

IR detectors and JWST, Planck SAFIR, Far-IR Interferometer,

cryocoolers Life Finder

Coronagraph Precursor mid-size Future filled-aperture

mission observatories

properties of terrestrial planets will be scientifically

most valuable within a broader framework that includes the properties of all planetary system constituents, including gas giants, terrestrial planets and

debris disks. TPF’s ability to carry out a program

of comparative planet studies across a range of planetary masses and orbital locations in a large number

of new solar systems is an important scientific motivation for the mission. However, TPF’s mission will

not be limited to the detection and study of distant

planets. An observatory with the power to detect

an Earth orbiting a nearby star will also be able to

collect important new data on many targets of general astrophysical interest.

The TPF observatory will likely take the form

of either a coronagraph operating at visible wavelengths or a large-baseline interferometer operating

in the infrared. The visible-light coronagraph concepts would use a single telescope with an effective

diameter of 8–10 meters, operating at room temperature, but required to achieve a billion-to-one
48

M I S S I O N S A N D T O O L S

image contrast. Very precise, stable control of the

telescope optical quality would be required. The

infrared interferometer concepts would use multiple

(≈4), smaller, 3–4-meter-diameter telescopes configured as an array and spread out over a large boom

of up to 40 meters or operated on separated spacecraft over distances of a few hundred meters. The

telescopes would operate at extremely low temperatures of ≈40 kelvin, and the observatory would necessarily be large. However, the image contrast

requirement, “only” a million to one, and thus the

required system optical quality, would be much

easier to achieve at infrared wavelengths.

TPF will perform system studies, science investigations, and technology development for both

architecture classes over the next several years. Final

selection of a TPF architecture will occur about

2006, based on the science and technology progress

of the next four years. Also, multimission architectures that take smaller steps toward the ultimate

scientific goal will be investigated.

The European Space Agency (ESA) has been

actively studying an infrared interferometer with

essentially the same science goals as TPF, usually

referred to as either Darwin or the Infrared Space

Interferometer (IRSI). Under a NASA/ESA Letter

of Agreement, scientists and technologists in both

agencies are discussing ways in which the preliminary architecture studies can lead to effective collaboration on a joint mission.

Missions Targeted to Enter Development

Phase in 2015–2020

A long-term Origins goal is the detailed study of

life and its evolution in ecosystems beyond the solar

system. Achieving that goal will require observations beyond those possible with TPF. For example,

searching the atmospheres of distant planets for

unambiguous tracers of life such as methane (in

terrestrial concentrations) and nitrous oxide would

require a spectral resolution of ~1,000, utilizing a

version of TPF with 25-meter telescopes. While a

Life Finder interferometer is beyond the horizon of

this strategic plan, except as a beacon for the technologists’ vision, the Single Aperture Far-Infrared

mission consisting of a single 8–10-meter telescope

operating in the far-IR could serve as a building

block for the Life Finder while carrying out a broad

range of scientific programs beyond JWST and

SIRTF. These include probing the epoch of energetic star formation in the redshift range 1<z<10

at a wavelength regime that can easily detect

continuum and cooling-line emission from dustThe James Webb Space

Telescope will be a

powerful generalpurpose observatory

capable of undertaking

important scientific

investigations into a

wide range of astronomical questions.
49

enshrouded primeval galaxies with an angular resolution capable of isolating individual objects at or

below the limits of the Hubble Deep Field; investigating the physical processes that control the collapse and fragmentation of molecular clouds to

produce stars of various masses by mapping of cold,

dense cores at <100 AU resolution at the peak of

their dust emission and using gas phase tracers such

as H2

, H2O, CO, OΙ, NΙΙ; learning about the era of

cometary bombardment that may have determined

the early habitability of Earth by making high spatial resolution maps of the distribution of ices and

minerals in the Kuiper Belts surrounding nearby

stars; and, studying the nature of the recently discovered objects in the Kuiper Belt of our own solar

system which may be remnants of our own planet

formation process.

construction phase of galaxies and quasars. Key

questions include: Where is the rest of the unseen

universe? What is the interplay of the dark and

luminous universe? How did the intergalactic

medium collapse to form the galaxies and clusters?

When were galaxies, clusters, and stellar populations assembled into their current form? What is

the history of star formation and chemical evolution? Are massive black holes a natural part of most

galaxies? A large-aperture UV/optical telescope in

space will provide a major facility in the second

quarter of the century for solving these scientific

problems.

The Far Future: Beyond 2020

Two missions still far in the future because of their

demanding technologies have strong relevance to

Origins goals. The first is the Life Finder, which

as described above would provide high-resolution

spectroscopy on habitable planets identified by TPF.

This information would extend the reach of biologists, geophysicists, and atmospheric chemists to

ecosystems far beyond Earth.

A second mission concept that appears promising is an interferometer capable of detecting the far

infrared and submillimeter light from the youngest

galaxies. JWST will study the visible starlight from

forming galaxies that has been red-shifted into the

near infrared by the expansion of the universe.

However, typically half, and sometimes more than

99% of the starlight of a galaxy is absorbed by dust

in that galaxy and re-radiated in the far infrared.

This emission is red-shifted further into infrared or

into the submillimeter bands. An interferometer

consisting of three 15–25-meter telescopes with a

1-kilometer baseline would have the sensitivity

and angular resolution (0.02 arcseconds at 100 micrometers) needed to study the physical conditions

in these young galaxies. In addition to cosmological

studies, the interferometer would be able to observe

collapsing protostars deeply embedded in their

parental molecular clouds, providing valuable constraints on models for star formation.

M I S S I O N S A N D T O O L S

SAFIR Technologies

Technology Builds on Leaves legacy for

past missions future missions

Large, passively JWST, TPF Life Finder

cooled optics

IR detectors and JWST, Herschel, Life Finder, Far-IR

cryocoolers Planck, TPF Interferometer

Large UV/Optical Telescope Technologies

Technology Builds on Leaves legacy for

past missions future missions

Large optics JWST, Visible light

Coronagraphic TPF complement to Life Finder

UV detectors HST, FUSE, Galex

A successor to HST operating at ultraviolet and

optical wavelengths, a large UV/optical telescope,

would produce forefront science in all areas of modern astronomy and would be focused on the era

from redshifts, 0<z<3, which occupies over 80% of

cosmic time, beginning after the first galaxies,

quasars, and stars emerged into their present form.

The science to be addressed in the post-HST era

includes studies of dark matter and baryons, the

origin and evolution of the elements, and the major
Enabling 5 Technologies

Abell 2218, a rich

galaxy cluster and

a spectacular

example of

gravitational

lensing. Light

passing through

the cluster is

deflected by its

enormous

gravitational

field, much as an

optical lens bends

light. This causes

the arc-like

pattern spread

across the picture

like a spider web.

Image: NASA/HST

CHAPTER
51

The technology plan has two strategic objectives.

In the near term, the maturing technologies for

observatories such as the Space Interferometry

Mission (SIM), the James Webb Space Telescope

( JWST), and the Terrestrial Planet Finder (TPF)

must be completed and tested. It is also critical to

begin establishing the new technological building

blocks for the very large space observatories described elsewhere in this roadmap that are envisioned to follow our current missions. Remarkable

progress has been made toward the near term

objectives. However, the longer term objectives are

not yet within our grasp. Creating the technological

capabilities to realize the observatories of the future

will require a new technology initiative. This initiative will develop advanced detector arrays to convert

the light into electrical signals; build large, lightweight mirrors; actively control the surface errors

of the mirrors and optical elements to produce an

almost perfect aperture; and provide cooling techniques to eliminate the infrared emission from the

optical surfaces of a warm telescope. These four

areas of focused technology development will provide the basic capabilities for a broad range of future

space observatory architectures.

...to invent tools for

The Origins technology program will develop the means to achieve the most ambitious and technically

challenging measurements ever made. These developments envisage new methods to gather signals from

distant sources, precise control of optical elements to a precision of one-thousandth of a human hair, and

measurements of distances between optical elements to the width of a hydrogen atom. Such exquisite

techniques require methods and tools that do not exist today. Building spacecraft of the future incorporating these technologies will exploit the creative inventiveness of our scientists as well as the care and

precision of our engineers.

T E C H N O L O G Y

a new age of discovery.

Accomplishments Following the Previous

Roadmap

Over the past five years, technology developments

leading towards the Origins missions have been

remarkably successful. The successes have been both

technical and institutional. Not only have new

space observatory components and capabilities been

developed, but also a number of valuable new partnerships with other government interests have

emerged.

HST is now the beneficiary of cryocooler

advances that have allowed the reactivation of the

NICMOS instrument and large format CCD

detectors that have increased the useable field of

view of the telescope. The Space Infrared Telescope

Facility (SIRTF) mirror is fabricated from a form

of beryllium metal that is optimized for cryogenic

optical system applications. This is a technology

that was initially studied and developed with the

help of NASA’s Aerospace Technology Enterprise.

SIRTF will carry improved infrared detector arrays

that are derived from technology originally developed by the Department of Defense (DoD).

51
52

Have you ever wondered

what animals look like in the

dark? The Education and Public

Outreach Office of NASA’s SIRTF

mission has created an infrared

zoo on the web.This website

has received numerous awards

and the seal of Good Housekeeping magazine.

Infrared light shows us the heat

radiated by the world around

us. By viewing animals with a

thermal infrared camera, we can

actually “see” the differences

between warmand coldblooded animals.

Infrared also

allows us to

Do Animals Glow in the Dark?

study how well

feathers, fur, and

blubber insulate

animals. Visitors to

the “Infrared Zoo”

see what new information you

can gather about the animals

here that you would not get

from a visible light picture.

Through its inventive use of

technology SIRTF involves

students in science and encourages conversations that

span discipline boundaries.

This is just one example of the

multidisciplinary educational

materials that are produced

with the goal of engaging the

young minds of the future

scientists.

T E C H N O L O G Y

52

– 80

–104.6

– 72.6

– 90

Degrees

Fahrenheit

– 80

– 89.8

– 67.2

Degrees

Fahrenheit

– 100

– 90

– 77.5

Degrees

Fahrenheit
53

JWST has sponsored significant work on demonstrating an array of 2,000 by 2,000 near-infrared

detectors which will benefit other IR missions.

Recent achievements in precision metrology and

reduction of microdynamic disturbances will enable

the SIM mission to achieve its goal of measuring

ultra precise stellar positions.

Progress towards the primary mirror for JWST

has come on two fronts. The Advanced Mirror System Demonstrator project, a partnership between

NASA and DoD, has produced a number of options for rapid fabrication of lightweight, 2-meter

mirror panels. These are the building blocks for

large apertures, such as JWST, that must be folded

to fit into the payload space of affordable rockets.

In parallel, techniques have been demonstrated to

deploy a folded mirror and align panels automatically in space to the accuracy desired for JWST.

Until recently, the TPF mission was envisioned

to be a starlight nulling interferometric instrument

that would operate at infrared wavelengths and have

a baseline of about 80 meters. Additional examination of extrasolar planet detection strategies and

technological alternatives has lead to a number of

architectural options that are now under study. The

options now range from the original separated

spacecraft infrared interferometer to structurally

connected interferometers and visible light coronagraphic telescopes.

We have also seen real progress toward an

architectural breakthrough in space optical systems.

With sufficiently accurate measurement and control, it will be possible to place the elements of a

single large aperture on individual separated spacecraft. The requirement is to be able to control a

constellation of spacecraft as if they were connected

by a rigid structure. It then becomes possible to

construct interferometers and sparse aperture telescopes with dimensions that exceed hundreds of

meters. These capabilities are being developed by

the StarLight portion of the TPF project.

These examples demonstrate the substantial

progress made in the technology areas envisaged in

Innovative, lightweight

mirrors and support

structures will make large

optical apertures in space

possible while keeping the

total mass constant.

our earlier roadmap. Nevertheless, our future technology needs have not yet been met. Staying on

the present course is clearly the most likely route

to success. We have also had success in identifying

common technology needs with other government

agencies and developing partnerships and shared

resources to find technological solutions.

Building Future Very Large Observatories

Detector Technologies

Detectors, the devices which convert light energy

to electrical signals, are the single most important

technology which determines the ultimate performance of our observatories. If the detectors fail to

do their job, the entire observatory system is seriously compromised. Technologies are poised to

T E C H N O L O G Y
54

make dramatic gains in detector performance at

far-infrared wavelengths and in the ultraviolet. In

the infrared, devices have not yet reached fundamental limits, and large format imaging arrays

(103

–104 pixels) have yet to be perfected. In the ultraviolet, new solid state devices allow simultaneous

detection of the both the intensity and wavelength

of the light. Several technologies should be explored, including semiconducting and superconducting devices, such as impurity band detectors

and transition edge sensors for imaging in the

40–600 micrometer band. In addition, very sensitive

detectors are needed for spectroscopy, including

coherent detectors at the longest wavelengths. It is

also in the more extreme domains that productive

partnerships with non-astronomical users of detector technology have not developed because there

is minimal commercial or military application for

the technologies needed by astronomers at long

wavelengths.

Detector technologies, while critically important

for the large visionary missions of the mid-century,

will also enable highly productive, smaller-scale

space investigations that might be developed in the

Explorer or Discovery programs.

To achieve their ultimate performance, these

new detectors will require improvements in small,

very low temperature, cryocoolers. In fact, the detector and its cryocooler should be viewed as an

inseparable technological pair. The TPF mission

is undertaking development of the next level of

cryocooler capability; however, the missions of the

far future will require further advances to enable

detector operation with sufficient sensitivity.

Space Optics Technologies

Usually, the largest and most massive component

of a telescope is its primary mirror. In order to

launch larger and larger telescopes into space with

our current launch vehicles, we must find a way to

keep the mass constant as the size increases. This

requires new precision materials and structures

that allow the mass per unit area, the areal density,

of the large optical elements to be reduced. The

JWST mirror technology program hopes to achieve

20 kg/m2

 over a 33-square-meter aperture. A

10-meter mirror that has the same total mass requires an areal density about 8 kg/m2

. Ultimately,

areal densities as low as 1 kg/m2

 may be required.

Active wavefront

control and ultraprecision laser

metrology under

development will

be key components of future

instruments.

T E C H N O L O G Y
55

Component

development of

high-performance

detectors and

cryocoolers lays the

foundation for the

next generation of

observatories.

Active Wavefront Error Control

As the areal density of the optical elements is reduced, they become more flexible and prone to

distortions induced from external disturbances.

However, the performance requirement on the overall optical system will remain close to perfect in order to achieve the benefits of going to space. This is

true even for JWST. As the telescope size increases,

there will be a growing need to actively sense and

control the shape of the optical surfaces. This will

be the only way to ensure the required optical performance as the thermal, gravitational, and mechanical disturbance environment changes in orbit.

Full Aperture Cryocooling

The largest of the Origins observatories will operate

at infrared wavelengths. In order to achieve the

highest possible performance, the telescope’s optics

must be cooled to prevent them from being a

brighter source of infrared energy than the astronomical targets. Cooling huge telescopes to temperatures close to absolute zero represents an

enormous challenge. Observatories that are located

at the Earth’s distance from the Sun require some

form of active cooling to reach the desired temperature of below 15 kelvin. If the telescope could be

placed beyond the orbit of Mars, it could be made

to naturally cool to the required temperature.

NASA’s new nuclear power and propulsion initiative may produce new flight options that will allow

space observatories to operate successfully in the

outer solar system, eliminating the need for a separate large aperture cooling technology.

Preserving Unique Space Science

Technologies

As new technologies appear, we often lose sight of

the important and continuing role of the older ones.

It is easy to assume that reliable devices will always

be there—reality has proven to be different. For

example, scientific CCD detectors are no longer always available, optical filter technology was recently

threatened by competing pressure for the same

manufacturing capabilities, and other spacecraft

components are no longer made. And, capabilities

required for scientific research are not always of

commercial or military interest, as we see in the farinfrared detector case. Where mature technologies

exist that are still a critical component of space science missions, NASA must take active steps to ensure that the manufacturing and testing capabilities

are preserved. The single most import area is preservation of the technology base for high performance

detectors that operate in the visible and infrared.

These devices are near their theoretical limits and

that capability must be retained.

T E C H N O L O G Y
6 Research

and Analysis

Keyhole Nebula,

approximately

8,000 light-years

from Earth. The

vantage point of

space reveals

details of the

nebula invisible

from the ground.

Image: NASA/HST

CHAPTER
57

The goal of the Origins Research and Analysis

(R&A) program is to provide the seed opportunities for scientists to investigate innovative ideas and

to do the fundamental research required to enable

the scientific objectives of the Origins theme.

Theoretical research and laboratory astrophysics,

combined with analysis of data from ground and

space observations leads to increased understanding

of astrophysical phenomena and forms the basis for

mission concepts. Innovative technology development begins in the R&A program through laboratory proof-of-concept demonstrations and the flight

of instrumentation on suborbital platforms such as

sounding rockets or balloons. The R&A program

also offers strong connections to universities and is

the breeding ground for future space scientists and

engineers. Finally, the loop is closed in the R&A

program where the return on investment in flight

missions is reaped through the analysis and interpretation of data.

Creating the Tools of Investigation

High-resolution imaging and spectroscopy at wavelengths ranging from the ultraviolet to the submillimeter is required for a variety of studies, including

those addressing the inflow and outflow of gases,

the structure of the cosmic web, radial and vertical

disk structure, grain growth chemistry, chemical

...to develop new experiment concepts,

The Origins Research and Analysis program provides scientists with the opportunity to explore innovative

ideas and technologies that lead to better understanding of astrophysical concepts and methods. This

fundamental research is crucial to achieving the scientific goals of the Origins program, and provides the

basis for many future mission concepts.

composition of the interstellar and intergalactic

medium, and the characteristics of planets around

other stars. In order to develop the required knowledge and technical capabilities, R&A efforts need

to be focused in the areas of detector development,

mission supporting technology, suborbital payloads,

laboratory astrophysics, and origins of solar systems.

Detector Development

The study of star and planet formation, interstellar

dust, and very distant and dusty objects calls for innovative detectors in the infrared and submillimeter

portion of the spectrum. Impurity band conduction

arrays, such as those aboard the Space Infrared

Telescope Facility (SIRTF), have proven remarkably successful, but must be further improved

for the Stratospheric Observatory for Infrared

Astronomy (SOFIA), the James Webb Space Telescope ( JWST), and the next generation of infrared

missions. New large format low read-noise and low

dark current, near-infrared arrays are vital to the

success of JWST. For other large infrared missions

of the future, including the Terrestrial Planet

Finder (TPF), a new generation of true photoconductor arrays, gapless bolometer arrays, or altogether new sensing technologies will be required.

For the far-infrared/submillimeter bands, further

developments in coherent detectors will be required.

In addition to advancing the state of the art of the

R E S E A R C H A N D A N A L Y S I S

and to create and to test theories of our Origins.

57
58

R E S E A R C H A N D A N A L Y S I S

Amazing Space is a set of

web-based activities developed for the classroom. The

program was designed to

enhance students’ science,

mathematics and technology

skills using recent data and

results from NASA’s Hubble

Space Telescope. The resulting

online multimedia resources

are the culmination of fiveweek summer workshops that

partnered teachers with scientists, graphic artists, writers,

and multimedia developers.

Each activity is a fun, interactive way to explore a topic that

adheres to National Education

Amazing Space

Standards for the target age

group. All activities include a

teacher guide that helps prepare educators to present the

lesson in the classroom. In the

guide, teachers find “science

background” information,

vocabulary, and detailed topic

information.

In the future, the Amazing

Space website will be updated

with additional downloadable

materials. The materials developed for educators and learners

of all ages are accurate, classroom-friendly, visually appealing, as well as carefully crafted

58

to adhere to National Educational Standards. By producing

and sharing classroom resources based on the Hubble

Space Telescope’s discoveries,

the Formal Education Group

hopes that visitors, young and

old, will enjoy learning about

the universe.
59

detectors themselves it will be important to improve

upon the readout technology used by infrared and

submillimeter detectors.

In the ultraviolet range, a multifaceted approach

is needed to develop more efficient detectors. New

circuit designs, backside treatments, mosaicing,

multiple device packing, and charge injection techniques are needed to improve the performance of

CCDs in the ultraviolet. Research on superconducting devices (such as superconducting tunnel junctions and transition edge sensors) suggests that they

have good sensitivity over the entire UV range and

provide broadband imaging, time tagging, and lowresolution, high-efficiency spectroscopy. Looking

ahead to space astrophysics missions of the future,

complementary metal-oxide semiconductor

(CMOS) active pixel sensors (APS) technology

offers extraordinary advantages over current CCDs.

An emphasis on early detector research is crucial

to the scientific success of a new mission. Concepts

for detectors on several missions including the

Hubble Space Telescope (HST), the Far-Ultraviolet

Spectroscopic Explorer (FUSE), and SOFIA were

initiated in the R&A program and brought to fruition in the focused technology program described

earlier.

Mission Supporting Technology

The R&A supporting technology program supports

the development of innovative proof-of-concept

ideas in a broad range of technologies that are relevant to the theme’s objectives.

 In the UV, the development of anti-reflective

coatings for mirrors and gratings is an important

area. Efficient grating designs, solar blind filters,

grid filters, UV calibration lamps, focal plane

shutters, interferometers, holographic gratings, and

visible coronagraphs are some of the supporting

technologies in need of further development.

Improved filter technologies which deliver larger

diameters and extend spectral coverage to longer

wavelengths are needed in the IR regime. In addition, cold analog-to-digital converters and improved support electronics are ripe for development.

 Suborbital Payloads

The R&A program offers an excellent opportunity

to develop small payloads for suborbital flights. In

particular, balloon or Shuttle-borne payloads produce cutting-edge science. Sounding rockets can

also be used as technological testbeds. Such flights

not only help to develop state-of-the-art technolR E S E A R C H A N D A N A L Y S I S

Sound waves in the

embryonic universe

are revealed for the

first time in this

image captured by

the BOOMERANG

balloon-borne

telescope during

its maiden voyage

around the Antarctic.

The patterns visible

in the image are

consistent with those

that would result from

sound waves racing

through the early

universe, creating

the structures that by

now have evolved

 into giant clusters

and super-clusters

of galaxies.

RA (deg)

80 90 100

Dec (deg)

b = 20

–50

–40

–45

–421 421.uK

–400 –200 0 200 400

B150A 1 dps
60

ogy, but also constitute a high yield investment in

human capital. Investigators that come through the

program have gone on to become principal investigators of flight missions, major instrument builders,

and astronauts.

Laboratory Astrophysics

By utilizing a combination of laboratory experiments, modeling, and theoretical calculations, the

laboratory astrophysics program provides the fundamental knowledge needed to make sense of data

collected by space missions or to plan them. Laboratory measurements are often an essential link between observations and scientific conclusions. The

program explores a tremendous breadth of topics,

from the very coldest regions deep in molecular

clouds to the extraordinary environments around

super-massive black holes. It supports NASA’s

space missions from conception to completion,

defining mission parameters and providing postflight analysis.

Ultraviolet laboratory spectroscopy supports

observations which test cosmological models and

provide a better understanding of the processes that

created the elements during the Big Bang. Spectroscopic data are key to interpreting visible and UV

spectra of important interstellar molecules, such as

the large organic species and diffuse interstellar

bands (DIBs) that may be connected to the origin

of life. Finally, combining laboratory results with

space data provides insight into the ages and

metallicities of galaxies, the sequence of galaxy

formation, as well as the energetics of interstellar

dust in a variety of environments.

Fine structure transitions of atoms and atomic

ions in the far-IR/submillimeter are the main cooling lines of the non-ionized interstellar medium.

This makes them key contributors to gravitational

collapse, and as such they are critical to understanding the formation of stars and planets. IR/submillimeter transmissions of interstellar dust grains

indicate specific mineral and carbonaceous composition, leading to grain opacities in various environments. These opacities, uncertain now by an order

R E S E A R C H A N D A N A L Y S I S

The National Virtual

Observatory will

connect digital sky

surveys, observatory

and mission archives,

and astronomy data

and literature services

into a single framework, enabling investigations otherwise

too resource intensive

to undertake.
61

of magnitude, are key to estimating the temperature

and mass of the interstellar medium within entire

galaxies.

Perhaps most importantly, future missions will

study Earth-like planets and search for signs of life.

Laboratory experiments have shown that some of

the raw materials for life on these planets can be

created in interstellar grains of ice and dust. It is

vital to continue these experiments, as well as others

aimed at understanding the potential biosignatures

observable spectroscopically on these planets from

space missions.

Origins of Solar Systems

The search for new solar systems by ground-based

techniques has been extraordinarily successful in the

last several years. These searches can be expected to

be increasingly successful in the next several years

and represent crucial inputs to the design of the

TPF mission. The R&A program will continue to

support these searches and will broaden the range

of techniques and opportunities.

However, the TPF program will require more

than just an inventory of the nearby planets. We

need to understand how planetary systems formed,

what determines their stability, and what determines the size of planets. These are research topics

to be pursued in the Origins R&A programs.

If the answer to “Are we alone?” is yes, we need

to have the background theoretical basis to understand why we are unique.

Theory and Data Analysis

Before a space mission can be designed, the scientific objectives of the program must be firmly supported by observation and theoretical calculation.

Recognizing this, the Origins program includes

important support for theory and archival research.

Theory

Theory provides the fundamental quests for our

programs, predicts observable and measurable phenomena, and drives mission and payload design

requirements. Theoretical tools are required for the

extraction and interpretation of essential science

from observational data.

Theoretical studies of early stars, galaxy formation processes, the physical processes of star, planet,

and disk formation and evolution, and models in

direct support of the search for extrasolar planets

are all essential to the Origins program.

Archival Research

As data from previous and ongoing NASA missions

accumulate, the value of archival research mounts.

Through the multi-wavelength data already available, researchers have gained a much better understanding of a variety of important and interesting

astrophysical phenomena without ever using a telescope. Such gains range from establishing universal

relations between disparate emission phenomena

such as the radio-infrared correlation in star-forming galaxies, to the identification of rare “RosettaStone” objects by comparing multimillion lists of

sources from different wavelengths. Though current

wavelength-specific archives are readily available,

their contents are growing exponentially in both

content and diversity. The development of more

sophisticated software tools permitting queries

spanning all available archives would prove invaluable to scientists. Such a collection of tools would

constitute a National Virtual Observatory, a powerful new research capability enabling investigations

otherwise too resource intensive to undertake.

R E S E A R C H A N D A N A L Y S I S
7

Andromeda

Galaxy, about

65,000 light-years

in diameter and

approximately

2.2 million lightyears from Earth.

This large spiral

galaxy is very

similar to our own

galaxy, the Milky

Way. The area

shown in this

image covers

about five times

the area of the

full Moon. Image:

NOAO/AURA/NSF

T.A. Rector, B.A.

Wolpa

CHAPTER

Engaging the Public
63

The Origins program seeks to answer questions

that have endured since humans looked into the

night sky from the first campfires. The age-old

questions “Where did we come from?” and “Are

we alone?” have always been part of humanity’s

need to understand our existence and place in the

universe. People have considered these questions

in the realms of religion, myth, the arts, and the

pop culture interest in the unknown.

Origins scientists use methods that integrate a

wide range of scientific disciplines from astronomy, physics, and chemistry, to geology and

paleontology, as well as micro- and evolutionarybiology. Sharing the results of the Origins quest

will require as diverse a set of tools in public engagement as in science. The ideas and discoveries

of the Origins program will expand people’s intellectual reach through the tools of science and the

unique vantage point of space. We can accomplish

this by seeking answers to fundamental questions

and sharing what we learn with all humanity.

Missions Create Opportunities

Each mission of the Origins program provides

unique opportunities to engage the public in the

journey of discovery.

The goal of the Origins public engagement program is to share our stirring quests and findings with people

of all ages and backgrounds, conveying the thrill of scientific discovery and technological accomplishment

in space. We strive to inspire Americans, to enhance scientific literacy nationwide, and to improve science,

mathematics, and technology education at all levels.

...to share, to inspire, to educate all Americans in

the adventure of discovering our origins.

The excitement of the launch, and the ongoing

drama of astronauts repairing and upgrading the

Hubble Space Telescope (HST) have been of

immense public interest during the first 12 years

of HST’s life. Images from HST have become

iconic, stimulating public excitement about space

science in ways never dreamed of at the time the

telescope was conceived. The future servicing

mission in 2004, and the proposed return to Earth

in 2010 to become a permanent exhibit at the

National Air and Space Museum, will provide

opportunities for public inspiration well into

HST’s second decade. The James Webb Space

Telescope will continue this tradition of including

the public in our explorations of the farthest

regions of space and time.

After its launch in early 2003, the Space Infrared Telescope Facility (SIRTF) will further open

the infrared window on the universe, permitting

observations in a region of the spectrum not fully

visible from beneath Earth’s obscuring atmosphere. This mission provides an opportunity to

engage both students and the general public in

perceiving the otherwise invisible world of the

infrared. Together with SIRTF, the Stratospheric

Observatory for Infrared Astronomy (SOFIA) is

uniquely poised to demonstrate the strength of

partnerships between missions with similar goals.

E N G A G I N G T H E P U B L I C

63
64

“In the past century and a half, a tragic divide has

developed and grown between science and religion

with regard to the origins of life, specifically human life.

This division is all the sadder because it is unnecessary,

and fails to take account of the best in both traditions.

As Albert Einstein once said, ‘In every true searcher of Nature there is a kind of religious

reverence, for he finds it impossible to imagine that he is the first to have thought out

the exceedingly delicate threads that connect his perceptions.’

If each of us were to become a ‘true searcher’, in realms both scientific and spiritual,

then I believe that we would all draw closer not only to our origins, but also to our

destiny: our destiny as enlightened beings able to live in peace with each other,

because we have reached a state of respect, tolerance and love that can only come

with the recognition that we are more alike than unalike, and that all humanity is

bound together by our very life on this planet.

Exploring the marvels of science—both on Earth and in space—is one of the best

ways to tap into the wonder of the universe and, consequently, the great potential of

humankind to create societies worthy of the tremendous physical gifts of creation. For

when we contemplate the fact that this grand universe is somehow at our disposal,

that its beauty, immensity, and mysteries touch our hearts in the deepest way, then we

come to understand that though a small part of the cosmos, we are, in fact, in touch

with the infinite—and therefore infinitely connected with each other. This realization

is the seed of peace.”

The Seed of Peace

Dr. Oscar Arias Sanchez,

Nobel Peace Prize

laureate and former

President of Costa Rica,

on whether the

search for origins can

bridge science, religion,

and spirituality and

hence contribute to

world peace.

Dr. Oscar Arias Sanchez was born in 1941. After studying in the United States, he read law and

economics at the University of Costa Rica in the capital, San Jose. As a student he engaged actively

in the work of the National Liberation Party. Having completed his degree, he went on to take a

doctorate in England, with a thesis on the subject of “Who rules Costa Rica?” Dr. Arias embarked

on his political career in earnest in 1970 and was elected President in 1986. As President, he was

instrumental in forging an accord between Costa Rica, Guatemala, El Salvador, Honduras, and

Nicaragua to bring peace to this region of Central America long torn by strife and civil war. For

this achievement, Dr. Arias was awarded the Nobel Peace Prize for 1987.

64
65

SOFIA is also an infrared observatory, but one

that uses a Boeing 747 aircraft to get above most

of Earth’s atmosphere. Teachers will work side by

side with scientists during observing flights, providing thousands of dedicated educators a chance

to participate in scientific research and discovery.

The Space Interferometry Mission will take

breakthrough technology into space to detect

Earth-size planets around distant stars. This

search for other Earths has the potential to ignite

public excitement and stimulate the public imagination akin to the greatest scientific discoveries in

the history of humankind.

An even more ambitious step in the search for

life outside our own solar system is the Terrestrial

Planet Finder. The direct detection of an Earthlike planet, including indications of a warm, wet

atmosphere will bring the search for life from

the realm of speculation and science fiction to

the workbench of scientific investigation. We will

need to be prepared to respond to the likely tremendous worldwide interest such a discovery

will cause.

Engaging a Broad Audience

The Origins public engagement program aims to

include all of the diverse members of the American public, with their varied backgrounds, wide

range of experience, and different ages. We will

reach them by forming a wide spectrum of partnerships, adopting a multimedia approach, integrating the perspectives of varying disciplines, and

strategically guiding such activities through the

Origins Education and Public Outreach Forum.

The involvement of scientists and engineers

will be critical to present the scientific goals and

results of Origins missions in greater depth, and

with a broader perspective, than their images and

discoveries alone provide. We recognize the skill

of making scientific results accessible for general

audiences while preserving intellectual authenticity as a quality that needs to be continually nurtured in interested scientists. These individuals

will help us build bridges between the science

realm and the lives of our audiences to extend the

missions into the classrooms and living rooms of

We engage the public,

teachers, and students

to implement NASA’s

vision to inspire the next

generation of explorers.
66

America. The public at large has a long-held

fascination with space. We will capitalize on

this fascination by showcasing the people

behind the discoveries and the technological

breakthroughs that enable them, thereby

providing a human element to the missions.

We will work with the existing public affairs

infrastructure of NASA to make scientific

discoveries and results gathered by the missions

promptly available in a news-oriented format.

We will involve in our planning members of

the communities we are aiming to serve, and

we will draw on teams of writers, producers,

and education specialists who have experience

with our audiences to make this information

understandable and relevant to the public.

Wherever possible we will create opportunities

for teachers and students to immerse themselves in the authentic process of discovery,

thereby showing them how scientists work and

how we progress from observations to scientific

knowledge.

An important element in achieving these

goals will be collaborative activities involving

diverse communities. To reach these diverse

communities we will need to use diverse means

of communication.

The partnerships we seek to forge will

connect:

• Science and education departments at

colleges and universities

• Scientists at colleges, universities, and

government agencies

• Museums, science centers, and planetaria

• Organizations serving traditionally

underserved groups

• School districts

• Libraries

• Community-based organizations

• Youth club organizations

All of the activities of NASA’s

Office of Space Science

engage the public at various

levels. In the context of a

science program such as

Origins, these levels fit

broadly into the following

categories:

Formal Education

K–14 curriculum materials,

teacher training and professional development, distance

learning programs.

Informal Education

Museum programs, planetarium shows, traveling

science exhibits and associated take-home materials.

Public Outreach

Public lectures, classroom

visits, educational videos,

interactive/educational

websites and software.

Each of these categories

interacts with every other

category. Typically, however,

public engagement activities

for science programs are

contained within one or two

categories.

Education and Public Outreach
67

Strategic Leadership

Strategic leadership will be provided by the Origins Education Forum, operated at Space Telescope Science Institute. The Forum will help

determine how the various mission outreach efforts fit into the broader educational context. It

will be proactive in seeking high-leverage opportunities to maximize the usefulness and effectiveness of material, programs and services created by

the Origins missions. The Forum will work with

missions to enhance activities targeted at formal

(K–14) education, informal education (e.g., exhibits), news, and online audiences in a manner that

minimizes duplication of effort and utilizes limited

resources for maximum effectiveness. The Forum

will coordinate distributed activities, and will serve

as an information resource for measuring the

impact of education and public outreach efforts

conducted by the Origins missions and research

programs.
68 Major Contribution Contribution

GROUND-BASED

R&A Keck KI LBTI

EMERGENCE OF THE MODERN UNIVERSE

How did the cosmic web of matter organize into

the first stars and galaxies?

1 Pristine gas, the first stars, and the first heavy elements

2 Black holes and structure in the early universe

3 Formation and evolution of galaxies

How do different galactic ecosystems (of stars and gas) form

and which can lead to planets and living organisms?

4 Lifecycle of stars in the Milky Way and other galaxies

5 Habitats for life in the Milky Way and other galaxies

STARS AND PLANETS

How do gas and dust become stars and planets?

6 Molecular clouds as cradles for star and planet formation

7 Emergence of stellar systems

8 Evolution of protoplanetary dust and gas disks into planetary systems

Are there planetary systems around other stars and how do their

architectures and evolution compare with our own solar system?

9 Evidence of planets in disks around young stars

10 Census of planetary systems around stars of all ages

HABITABLE PLANETS AND LIFE

What are the properties of giant planets orbiting other stars?

11 Chemical and physical properties of giant extrasolar planets

12 Detect giant planets by direct imaging, and study their properties

How common are terrestrial planets? What are their properties?

Which of them might be habitable?

13 Which nearby stars host terrestrial planets that might be suitable for life?

14 Atmospheric compositions of terrestrial planets orbiting nearby stars

Is there life on planets outside the solar system?

15 Optimal biosignatures for life on other worlds

16 Evidence for life on planets orbiting nearby stars

1

2

4

5

6

7

3

Research Area One

INVESTIGATIONS

Research Area Two

INVESTIGATIONS

Research Area Three

INVESTIGATIONS

Research Area Four

INVESTIGATIONS

Research Area Five

INVESTIGATIONS

Research Area Six

INVESTIGATIONS

Research Area Seven

INVESTIGATIONS

Science Summary
69

SPACE-BASED

Origins missions flow from

the research areas and

investigations in this roadmap.

Opt/IR Large

Coronagraph UV/OPT

HST FUSE SIRTF SOFIA Mission Kepler SIM JWST TPF SAFIR Mission
Advanced Camera for Surveys

Active Galactic Nuclei

Active Pixel Sensors

Astronomical Unit

Atacama Large Millimeter Array

Balloon Observations of Millimetric Extragalactic

Radiation and Geophysics

Complementary Metal Oxide Semiconductor

Cosmic Background Explorer

Charged-Coupled Device

Cosmic Origins Spectrograph

Canadian Space Agency

Diffuse Interstellar Bands

Department of Defense

Education/Public Outreach

European Space Agency

Far-Ultraviolet Spectroscopic Explorer

Giant Segmented Mirror Telescope

Hubble Space Telescope

Habitable Zone

Intergalactic Medium

Infrared

Infrared Space Interferometer

Glossary

ACS

AGN

APS

A U

ALMA

BOOMERANG

CMOS

COBE

CCD

COS

CSA

DIBS

DoD

E/PO

ESA

FUSE

GMST

HST

H Z

IGM

I R

IRSI

70
ISM

ISO

JCMT

JWST

K I

LBT

LBTI

L F

LISA

MAXIMA

NASA

NICMOS

NVO

PAH

R&A

SAFIR

SCUBA

SIM

SIRTF

SOFIA

TPF

U V

WFC 3

Interstellar Medium

Infrared Space Observatory

James Clerk Maxwell Telescope

James Webb Space Telescope

Keck Interferometer

Large Binocular Telescope

Large Binocular Telescope Interferometer

Life Finder

Laser Interferometer Space Antenna

Millimeter Anisotropy eXperiment IMaging Array

National Aeronautics and Space Administration

Near-Infrared Camera and Multi-Object Spectrometer

National Virtual Observatory

Polycyclic Aromatic Hydrocarbon

Research and Analysis

Single Aperture Far-Infrared Observatory

Submillimeter Common-User Bolometer Array

Space Interferometry Mission

Space Infrared Telescope Facility

Stratospheric Observatory for Infrared Astronomy

Terrestrial Planet Finder

Ultraviolet

Wide-Field Camera 3

71
EPILOGUE

Origins Horizon

Born of the extraordinary accomplishments of

20th century physics, astronomy, geology, and

biology, the Origins program takes up the challenge of answering questions as old as our species. When Galileo first turned his tiny telescope

to the night sky, he saw the Milky Way resolved

into millions of stars, in one stroke expanding our

grasp of the universe to a scale that had not been

imagined from the sight of eyes alone. The growth

of scientific culture and tools over the next three

centuries revealed a vast realm, each at-first-incomprehensible discovery assimilated into an

increasingly uncomfortable reality. The eruptive

growth of 20th century astronomy has brought us

an appreciation of how vast, old, and unearthly

the universe is, and has left humanity struggling

for a sense of our own significance consistent

with the reality of who and what we are. But science has also given us something that will help,

by promising answers to our ancient questions:

Where do we come from? Are we alone? When

the answers to these questions are known, our

civilizations will evolve new visions of who we are

and what our futures might be. Already we have

learned enough to appreciate that the universe

is enormous and ancient, but life—tiny and

transient—is its precious jewel.

Where do we come from?

Are we alone?

When the answers to

these questions are

known, our civilizations

will evolve new visions

of who we are and what

our futures might be.

72
In the first few decades of this new century

astronomers will largely complete the study of

cosmology: the description of the universe on the

largest scales and how it works. With the Space

Infrared Telescope Facility (SIRTF) and the James

Webb Space Telescope (JWST) we will also begin

to write the final chapter of the story of galaxies,

witnessing the actual birth of these continents of

stars. In particular we will chart the13-billion-year

history of the Milky Way Galaxy we inhabit, understanding how the materials for new stars, planets,

and life were generated and distributed. SIRTF

and JWST will also lead the way in studying the

birth of stars with their families of planets, moons,

comets, and asteroids, the cosmic Petri dish of life.

Led by the Terrestrial Planet Finder, we will peer

one-by-one at our hundreds of nearest neighbor

stars and inventory their planets, searching for

solar systems resembling our own with a balmy,

wet planet like Earth. It will require much more

ambitious telescopes such as Life Finder to detail

the conditions of such a world, gathering far more

light from a distant world, enough to see the

signatures of life in the atmospheres of planets,

evidence for seas and continents, for seasonal

variations. We cannot yet know whether the

worlds we seek are common or exceedingly rare,

so our journey may eventually involve great

flotillas of large telescopes that can

73
extend the search to thousands or tens of thousands of stars. By the middle of the 21st century,

the Origins program could be compiling a vast

catalog of tens of thousands of solar systems and

monitoring the weather, climates, seasons, and

biochemistry on hundreds of inhabited worlds.

Machines almost beyond today’s imaginings will

be needed to scrutinize and perhaps even image

the worlds we humans might someday visit, but if

the will and spirit hold, physics says it can be done.

Will we humans leave our home in the solar system and begin to migrate over the Milky Way as

we once spread over the Earth? From our view at

the beginning of this new century it seems both

inevitable and impossible. But, whether we make

these future settlements in body or only in mind,

our journey has surely now begun, and when

we first find, in the orbit of a neighboring star, a

planet resembling Earth, one where human beings

might conceivably live, the quest could become

an obsession. Perhaps our descendants will praise

us for our initiative, perhaps they will curse the

relentless curiosity that propels humans into

greater accomplishments and greater peril, but

our part in this drama is preordained, its resolution beyond our time and imagination, barely

within our dreams. We go on.

— Alan Dressler

74

EPILOGUE
ORIGINS SCIENCE SUBCOMMITTEE MEMBERS

Alan Dressler (Chair)

Carnegie Observatories, Carnegie

Institution of Washington

Louis J. Allamandola

NASA Ames Research Center

Omar Michael Blaes

University of California Santa Barbara

Adam Seth Burrows

University of Arizona

Robert J. Hanisch

Space Telescope Science Institute

George Helou

California Institute of Technology

Lynne A. Hillenbrand

California Institute of Technology

James E. Larkin

University of California Los Angeles

Robert W. Noyes

Smithsonian Astrophysical Observatory

William Oegerle

NASA Goddard Space Flight Center

Alycia J. Weinberger

Department of Terrestrial Magnetism,

Carnegie Institution of Washington

Hashima Hasan (Executive Secretary)

NASA Office of Space Science

ADDITIONAL CONTRIBUTORS

This Roadmap

would not

have been

possible

without the

efforts of

the following

people:

Charles Beichman

Jet Propulsion Laboratory

Dave Black

Lunar and Planetary Institute

Chris Blades

Space Telescope Science Institute

Andy Boden

Jet Propulsion Laboratory

Bob Brown

Space Telescope Science Institute

Preston Burch

NASA Goddard Space Flight Center

Jim Burge

University of Arizona

Richard Capps

Jet Propulsion Laboratory

Dan Coulter

Jet Propulsion Laboratory

Phil Crane

NASA Office of Space Science

William Danchi

NASA Goddard Space Flight Center

Rolf Danner

Jet Propulsion Laboratory

Navid Dehghani

California Institute of Technology

Michael Devirian

Jet Propulsion Laboratory

Dave Gallagher

Jet Propulsion Laboratory

Tom Greene

NASA Ames Research Center

Ian Griffin

Space Telescope Science Institute

Fred Hadaegh

Jet Propulsion Laboratory

Kate Hartman

NASA Goddard Space Flight Center

Isabel Hawkins

University of California at Berkeley

Phil Hinz

University of Arizona

Garth Illingworth

University of California Santa Cruz

Cliff Imprescia

NASA Ames Research Center

Ken Johnston

US Naval Observatory

Jim Kelley

Jet Propulsion Laboratory

Shri Kulkarni

California Institute of Technology

Kenneth Lang

Massachusetts Institute of Technology

Jesse Leitner

NASA Goddard Space Flight Center

Marty Levine

Jet Propulsion Laboratory

Charles Liu

American Museum of Natural History

Leslie Livesay

Jet Propulsion Laboratory

Jonathan Lunine

University of Arizona

Geoff Marcy

University of California at Berkeley

Jim Marr

Jet Propulsion Laboratory

Craig McCreight

NASA Ames Research Center

Thomas McMahon

University of Arizona

Victoria Meadows

Jet Propulsion Laboratory

Karla Miller

Jet Propulsion Laboratory

Mike Moore

NASA Office of Space Science

Ben Parvin

Jet Propulsion Laboratory

Carl Pilcher

NASA Office of Space Science

Doug Richstone

University of Michigan

George Rieke

University of Arizona

Anneila Sargent

California Institute of Technology

Sara Seager

Carnegie Institution of Washington

Bernie Seery

NASA Goddard Space Flight Center

Mike Shao

Jet Propulsion Laboratory

Cathy Siffert

Jet Propulsion Laboratory

George Sonneborn

NASA Goddard Space Flight Center

Peter Stockman

Space Telescope Science Institute

Wesley Traub

Smithsonian Astrophysical Observatory

Steve Unwin

Jet Propulsion Laboratory

Randii Wessen

Jet Propulsion Laboratory

Guy Worthey

Washington State University

Erick Young

University of Arizona

Jonas Zmuidzinas

California Institute of Technology
National Aeronautics and

Space Administration

Jet Propulsion Laboratory

California Institute of Technology

Pasadena, California

JPL 400-1060 10/02