Relationships between chondritic meteorites and planets

Abstract

Chondrites formed in the solar nebula prior to the formation of planets; they probably constituted the bulk of preplanetary solids in the inner solar system. In the highly reduced enstatite chondrites 10% of Si is metallic; in the highly oxidized CM and CI chondrites 20-30% of Fe is in the +3 state. The high density of Mercury implies that nebular Fe was reduced, whereas the low density of Mars indicates that a large fraction was oxidized. Most rare gases in the terrestrial planets seem to have accreted trapped in grains; Venusian interelement ratios resemble those in enstatite chondrites; Earth and Mars ratios are more like those in ordinary or carbonaceous chondrites. These observations imply that enstatite chondrites formed near the Sun (near Venus?), the carbonaceous chondrites formed far from the Sun, the ordinary chondrites at an intermediate location. Compositional data on Mercury, comets, an asteroidal fragment, and the moons of Mars are badly needed.