Meteorites are rocks which fall to the earth from space. There are three basic types, stones, irons and stony irons, each of which will be discussed below. But first, where do meteorites come from? The vast majority come from the asteroid belt, a zone of millions of rock fragments orbiting between Mars and Jupiter. These fragments never managed to collect into a planet as did the rock fragments in the other planetary distances from the Sun. The various fragments in the asteroid belt have orbits which range from circular to very oblong and which also have orbits which are not in the same flat plane. Over time, because of these different orbits, many crash into each other, thereby deflecting some of them out of their original orbits within the asteroid belt, into new "earth-crossing" orbits which bring them to earth as meteorites.
Although most meteorites come from the asteroid belt, a few are now known to be from Mars and a few from our Moon. The origin of these rare meteorites, however, is also related to earlier action within the asteroid belt. Just as some asteroid fragments come to earth, some of these fragments impact Mars or the Moon with enough energy to dislodge rocky pieces of those two bodies. As these dislodged pieces escape from the impact site, they orbit in space until they happen to reach the earth. How do we know these rare types are from Mars or from the Moon? The basic answer is that their chemistry is different from asteroid chemistry.
Click on the pictures below to learn more about the three major meteorite types: