Asteroids: the big picture

During the past 15yr much progress has been made in the study of the asteroids with optical, infrared, and radar telescopes. Simultaneously a vast body of petrologic, chemical and isotopic data has been acquired for meteorites. This work has demonstrated that asteroids vary widely in composition and thermal history in a systematic but complex way with orbital position and size. It appears that these variations can be explained to first order by a simple model invoking three principal mechanisms: 1) condensation of chondritic material at radial locations in the nebula; 2) intense metamorphic heating after accretion which declined rapidly with both increasing solar distance and smaller planetesimal size; and 3) complex collisional fragmentation. -from Authors