reply to post by iforget
Conversely I wonder what prevents Vesta from accumulating debris and growing into a full fledged planet?
I would go with the presumption that the influence of Jupiter is to blame. This is mentioned often.
The great mass that Jupiter possesses served as a sort of "clearing house" in a sense early in the formation of the Solar System, and prevented the
accretion of the dust, debris and other material that was accumulating at the orbital range that is the location of the "Asteroid Belt". Had
Jupiter not been so massive, there very likely would have been another rocky planet, perhaps similar to Mars in size, at that location.
The "final result" of any planetary system as it forms is most likely going to be due to the distribution of the initial conditions, and how the
dust and gases are arranged, and then the chaotic way that they will interact, as they coalesce. In addition, there can be outside influences during
this process, that alter the arrangements. Without a time machine, we will always be making educated guesses on this, and will get more information
as many observations can be made of
other star systems being born, and seeing the various stages of development.