- Roughly 2 million rocks between Mars and Jupiter.
- Largest object, Ceres, is about 1000km across, but most objects are much, much smaller.
- Only a few are 'planets'.
- Only contains about 0.02% the mass of the Earth
- Originally contained much more stuff.
- But, it lost most mass, but how? Collisions or dynamics?
- See lots of evidence for collisions: