Teach Astronomy - Evidence of Formation

http://www.teachastronomy.com/
Interplanetary debris gives astronomers evidence of the formation process of the solar system. Icy material like cometary debris has never been significantly heated in the 4.6 billion year history of the solar system. Interplanetary dust grains are probably cometary debris, and they filter though the upper atmosphere. The air forces have airplanes that can scoop these up as an enormous air filter, and scientists analyze the tiny particles that result. Larger rocks of course hit the Earth. Asteroids are also left over material from the formation of the solar system and the accretion of planetesimals, and meteors and meteorites form the residue of asteroids. A fine rain of meteorites hits the Earth all the time. All but the largest ones are hard to find, so astronomers go to the Antarctic ice pack to collect meteorites, moving around the cool blue ice with sticky rollers where the small rocks that fall from space are obvious. This work supports the sequence of formation: a nucleus of rocky, metallic material eventually covered by sooty, carbonaceous material and coated at later stage with ices.