Origin of differentiated meteorites

Abstract

The larger asteroids with low inclination in the inner portion of the asteroid belt are evaluated as sources of differentiated meteorites (irons, stony irons and achondrites). It is found that the calculated earth impact rate is in agreement with the observed flux of these bodies. The frequent occurrence of elapsed times before impact of 0–1000 m.y. is in agreement with the observed typical exposure ages of iron meteorites, and the observed occurrence of some very young (< 100 m.y.) exposure ages. The absence of many > 1000 m.y. iron meteorite exposure ages and > 50 m.y. achondrite exposure ages must be attributed to collisional destruction as the calculations predict a significant number of these older ages. The calculated geocentric velocities are almost always low enough to permit penetration of the atmosphere. The distribution of elongation of the radiants shows an excess in the direction of earth's antiapex, but not sufficient to produce a significant afternoon excess. Although contributions from other sources are possible, these objects appear to be the most plausible sources of differentiated meteorites. Chemical and isotopic data on these bodies suggest a relationship to the earth and moon, and it may be that they represent residual material from earth's accretional zone.