Why is a minor planet minor?

Abstract

ALL planets and satellites are generally believed to have formed by accretion of small bodies. The craters on the Moon, Mercury and Mars give clear evidence that the accretion of small bodies was of major importance, at least during the last phase of their formation. It is very likely that collision and fragmentation of planetesimals played a key part in the accretionary stage of planets. As suggested by Hartung¹, accumulation and fragmentation of planetesimals may have competed in the planetary accretion process, and a planetesimal which could survive catastrophic destruction may have become a planet. On the basis of the accretion model of planet formation, we propose a new idea in which we explain why minor planets are ‘minor’ and could not grow to a full-size planet. These results also substantiate Orowan's² idea that terrestrial planets accreted inhomogeneously, with iron being the first to accumulate and silicates the second.