The survival of presolar grains in solar system bodies

Presolar grains can be found in the least altered members of all chondrite classes. These grains a sited in the fine-grained ''matrix'' of each meteorite, and their matrix-normalized abundances are governed by the metamorphic history of the host meteorite. Once the effects of metamorphism have been accounted for, the initial diamond abundances in all chondrite classes studied and the initial SiC abundances in most classes are found to be remarkably similar. This suggests that all chondrites sampled the same mixture of presolar grains, most plausibly the mixture inherited from the sun's parent molecular cloud. CI and CM2 chondrites appear to have acquired the least altered sample of this mixture of presolar grains. In other classes, the pre-metamorphic abundances of presolar materials correlate with bulk compositional properties of the host meteorites. This implies that currently recognized presolar grains are only part of a much larger reservoir of presolar material that was processed to different degrees in the nebula to produce the various meteorite classes. Relative abundances of different kinds of presolar grains can serve as probes of these processes.