Page 284 - NS-2 Textbook

ASTRONOMY 279

contracted more rapidly than the rest of the cloud and gen atoms in its interior. These atoms fueled the ther-
formed the "proto-Sun." monuclear fusion process.
In the cold depths of the cloud surrounding the Proto-Earth and the other proto-planets were born as
proto-Sun, certain gases combined to form compounds whirling clouds of ice particles and solid fragments-
such as water and ammonia. Solid dust and metallic each a cosmic dust storm. Later this material collected
clystals appeared. Gradually, forces in the spinning into balls. Gradually these proto-planets grew by the ac-
cloud flattened it into the shape of an enormous disk. At cumulation of cold dusts from the region of space near
a great distance, this disk would have looked somewhat them. (Even today, planets continue to sweep up dust
like a gigantic revolving phonograph record, with the and meteorites.)
protO-SW1 at the center. In time radioactive elements and the compressive ac-
Within this whirling disk, eddies and swirls contin- tion within the cold Earth began to give off heat. After
ued to appear. Some ·were torn apart in collisions, while millions of years the temperature became high enough to
others were broken up by the growing gravitational pull melt the materials at Earth's center. The iron, nickel, and
of the proto-Sun. As this battle continued in the wheeling other heavy metals spread tluoughout the ball then
system, some local swirls gained material and others lost began to sink, forming the molten core of the planet.
it. Finally, a nmnber of these swirls became swirling Later, molten rock outside the core (magma) broke
disks large enough to hold together under the strength of tluough fissures to the surface. This allowed molecules
their own gravitational fields. Each was a proto-planet, of hydrogen, water vapof, and other gases to escape, cre-
moving tluough space around the Sun and sweeping up ating an atmosphere above the planet's surface. The
material left over from the original cloud. oceans ·were formed ·when the water vapor released into
As the proto-Sun's mass was pulled togethel~ colli- the atmosphere began to condense and precipitate. The
sions, compression, and radioactivity heated the mass lighter gases, especially hydrogen, did not stay in the at-
until temperatures at the center reached millions of de- mosphere long. They left behind a high concentration of
grees C. In a process called thermonuclear fusion, hydro- the heavier, rare elements of the universe------.-.-elements es-
gen atoms fused (combined under great pressure and sential for the formation of rocks, plants, and our own
temperature) to form helimn. This process is the source bodies.
of the energy that has kept the Sun ablaze ever since. TIlere are other theories of the creation of the uni-
The thermonuclear fusion at the core of the proto- verse and the solar system, of course. The foregoing sci-
Sun released large amowlts of energy and caused the entific theory is the one accepted by most modern-day
proto-Sun to shine. At first a dull red, in time it became cosmologists. Perhaps with more nmnerous and better
the golden yellow star that we see today. Because it was satellite-based telescopes, exploratOlY sites on the Moon
about 100 tinles larger in diameter than the largest of the and beyond, and further explorations in outer space,
proto-planets, it became a star instead of a planet. Its one day we will be able to shed more light on this fasci-
gravitational pull was strong enough to trap light hydro- nating topic.