Evening star., 1942-09-15
Of Stors, Men
And Atoms
Notebook Of Science Progress
In Laboratory, Field
And Study
By Thomas r. Henry.

"c1aiiiC hydrogen MAY CoII1poSS hie
outer shells of the gigantic planets
Jupiter and Saturn.
Hydrogen Is ordinarily the lightest Of
gases-the most ETHEREAL substance in
creation from which all the other ele-
ments presumably have been built up.
But under the extreme pressures and
low temperatures to which it is sub
jected on these planets, it probably takes
on solid form essentially indistinguish-
able from metal.
This is the conclusion of DR.. c. L.
Critchfield, Harvard University physicist,
now reported in the University of Chi
cagos journal Of Astrophysics.
Pure hydrogen, he suggests on the basis
Of his calculations, may form the outer
shells of the planets to depth of about
half their radii. The outmost layers of
these shells, he believes, consist of highly
compressed but otherwise gaseous hydro
gen. In the innermost layers. however,
the gas is compressed to such an extent
that it forms a peculiar, and as yet un-
discovered, form Of metal
1t previously had been computed that
the intermediate layers of the planets
have a density approximately equal to
that of water, and the suggestion had
been made that they may be formed of
ice. But the metallic hydrogen hypothesis,
DR.. Critchf1eld holds, fits the facts Just
as well. He computes that this metallic
shell has sufficiently large heat con-
ductivity to carry off enough of the heat
produced by radioactive elements in the
planets core to prevent the metal from
melting.
Astronomers have calculated that the
giant planets carry a fairly light shell
because their f1attening at the poles, al
though conspicuous, is less than 1t should
and similar period of rotation around
its axis. They concluded many years
ago that Jupiter and Saturn had inner
cores consisting of heavy elements, such
as iron, and an outer shell with a density
less than that of water.
The tremendous star explosions known
as supernovae will occur about once
every $50 years in the average galaxy
of stars, 1t recently has been calculated
by DR.. Fritz zwicky of the California
Institute of Technology
There are about so 900 900 900 stars in
the galaxy of which the solar system is
part. Some are "dead"-long since
past the possibility of exploding. As
Stunning that any one of the others is
just as likely to suffer one of these
titanic blasts as it's neighbor, DR.. Zwicky
calculates the sun has q $3.50 chance
that 1t will avoid becoming a supernova
for more than 100 600, 900 900 years.
Supernovae are stars which explode
with such force that for periods of
months they radiate as much heat and
light as a million suns The first was
discovered in 1872 by the Danish as
tronomer, Tycho Brahe, who suddenly
observed new star as bright as Venus,
which could be seen in full daylight.
Astronomers since have learned that
minor explosions take place every few
months in the earth's galaxy Such an
explosion Is known as a nova" After
the first supernova was seen by Brahe
37O years ago there was one other 80
years later, and none since. Until DR..
Zwicky started his work there was no
way of estimating how often such out
bursts might occur.
Six years ago he set up atop Mount
Palomar in California an 18-inch pho
tographic telescope, with which he pho
tographed on every clear, moonless night
as many rs possible of the thousands
of galaxies outside the Milky Way sys-
tem-most of them comparable in size
to the Milky Way galaxy itself. They
are similar in structure to the earth's
system of stars, but are millions of light
years distant.
In the course of his study to date Dr.
Zwicky has found IL supernovae, some
OF which were brighter than the entire
light emitted by the average galaxy BY
statistical analysis, he was able to esti-
mate one such explosion every $50 years
IN such n gigantic star system.
But any live star might explode
tomorrow, 50 far as the astronomers
know Two such blasts might take place
In year-and none other for a thou
sand years. No entirely satisfactory
hypothesis has been evolved to explain
such events.