Evidence for interstellar SiC in the Murray carbonaceous meteorite

Abstract

Silicon carbide has been observed in the interstellar medium and in circumstellar shells. Although it might be expected to occur in primitive meteorites that contain other kinds of pre-solar material, it has not previously been found. We have identified silicon carbide in two separates from the Murray carbonaceous chondrite that are enriched 20,000-fold in isotopically anomalous neon (Ne-E) and xenon (Xe-S)¹. An accompanying letter² reports on the isotopic composition of the two separates. The SiC is present in the form of crystalline grains, 0.1–1 µm in size. Cubic and {111}-twinned cubic are the most common ordered polytypes observed so far. The anomalous isotopic composition of its carbon, nitrogen and silicon indicates a pre-solar origin, probably in the atmospheres of red giants. An additional silicon- and oxygen-rich phase shows large isotopic anomalies in nitrogen and silicon, also associated with a pre-solar origin.