at the moment it looks to me, the theory, that the asteroid belt was formed from the material left over, when our solar system was formed, is more recent.
But if it's truly "left over", how do you account for iron meteorites, which are (generally?) assumed to be the cores of these "missing" planets....leftover random junk wouldn't have formed to the mass to generate the thermal activity to differerniate into solid metal, would it?
