Radiogenic and Cosmic-ray Exposure Ages of Meteorites, their Orbits and Parent Bodies

Abstract

Age determinations on meteorites provide information about the history of meteorites. The normal chondrites were produced in more than one, but not many, events. The distribution of the cosmic-ray exposure ages is consistent with the Moon and the Apollo asteroids as parent bodies for the H-group chondrites. For the L-group chondrites, these objects can be excluded; their parent bodies have to be found outside the orbit of the Earth, i.e. Mars or Mars asteroids. Many indications favour two large parent bodies (Moon and Mars) for the H- and L-group chondrites as compared to two groups of small parent bodies being fragments of two primary bodies. The chondrites represent material from the surface layers, i.e. from depths < 1 km of their parent bodies. Accumulation of solar wind particles as the source of the unfractionated component of carbonaceous chondrites is suggested.