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Asteroids
Asteroids and meteors represent remnants of the planet building process
in the inner Solar System. Asteroids are mainly composed of the metal
iron, while others are stony and some contain a mixture of organic compounds,
the basic building blocks of life. The October 1991 fly-by of the asteroid
Gaspra by the Galileo spacecraft, revealed an irregularly shaped rock
with craters, resembling a small moon. Asteroids are found predominantly
in the asteroid belt between Mars and Jupiter. Asteroids rang in size
from the largest known, Ceres, with a diameter of 930 kilometres, to the
microscopic dust particles.
Jupiter, the asteroid ring master
Where other material in the Solar System has accreted or come together
to form the planets, the region of the Solar System between Mars and Jupiter
has not formed any large planets. It is thought that the huge gravity
of Jupiter, sweeping by the asteroids, is continually pulling the ring
of rocks and dust apart, not allowing the natural process of planet forming
to occur.
The orbits of asteroids are not all circular or held between Jupiter
and Mars. Some even travel in orbits that cross the orbit of the Earth,
providing the possibility for collisions to occur. Although very rare,
collisions with relatively large asteroids can be devastating. The extinction
of the dinosaurs is thought to be due to an asteroid impact occurring
some 65 million years ago, in what is known as the Gulf of Mexico. More
commonly, the impacting objects are much smaller, appearing in the sky
as "shooting stars" and reaching the Earth's surface as meteorites.
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Jupiter, the asteroid ring master
