Asteroids as meteorite parent-bodies: the astronomical perspective

Abstract

A review of astronomical evidence suggests that asteroids are the parent-bodies for most meteorites. The surfaces of most asteroids are like carbonaceous chondrites while a significant minority are of stony-iron composition. Other meteorite types are recognized in the belt but are rare. Plausible dynamical processes are known that can deliver meteorites from the main belt to Earth. Asteroid compositions tend to correlate with solar distance, suggesting that the boundary between ordinary and carbonaceous chondritic nebular condensates was near the inner edge of the present belt. The size distribution of stony-iron asteroids implies they are remnant cores of ~ 100 differentiated bodies subjected to collisional fragmentation by carbonaceous objects initially ~ 300 times more numerous than now. Incomplete evidence on parent-body collisions exists in data on Hirayama families, asteroid lightcurves, and the compositional homogeneity of individual asteroids. Modern-day asteroid regoliths are thin and cannot have been environments for formation of most brecciated, gas-rich meteorites; such meteorites formed during early accretion of the asteroids. A scenario for the origin and evolution of meteorite parent-bodies is presented which includes: 1. (1) interruption of planet-formation by processes due to Jupiter; 2. (2) substantial asteroidal collisions during the first 0.5 b.y.; 3. (3) formation of most meteorite types within the differentiated bodies.