Interstellar Grains in Meteorites: Diamond and Silicon Carbide

Abstract

Well-preserved interstellar grains occur in carbonaceous chondrites. Diamond (10-100å) contains r - and p -process Xe (suggesting a supernovae connection), and appears to have formed by stellar condensation, not by interstellar shocks. SiC (mainly 0.1-1 μm) is labeled either with s-process Xe, Kr (red giant?) or with Ne 22 , N 15 (nova?), and shows large isotopic variations in N (100x), C (16x), and Si (1.3x). As Si is unaffected by H, He -burning, the Si variations reflect the isotopic heterogeneity of the ISM on the scale of individual stars; the Si compositions found thus far require at least 6 separate stars.