Wednesday, June 30, 2010

The asteroids

Most of the thousands of known asteroids, or minor planets, move in a belt on the large gap between Mars and Jupiter. The largest, Ceres, the first to be discovered, is only 930 Kms across, and only 200 are more than 100Kms across. They are too small for their own gravity to pull them into a spherical shape. They fall into types that match the meteorite types.
 The asteroids are probably debris left over from the birth of the Solar System, debris that failed to coalesce into a full sixed planet because of the disturbing gravitational pull of Jupiter. Some of them were deflected by collisions or close encounters into orbits outside the main asteroid belt. The so called Earth grazers come within Earth’s orbit. Other asteroids have been observed moving beyond the orbit of Saturn, and there may be more. Two groups of asteroids share the orbit of Jupiter, one 60. Ahead of the planet and another 60. Behind.