Large isotopic anomalies of Si, C, N and noble gases in interstellar silicon carbide from the Murray meteorite

Abstract

Primitive meteorites contain several noble gas components with anomalous isotopic compositions which imply that they—and their solid 'carrier' phases—are of exotic, pre-solar origin. Having enriched two of these gas components by a factor of ∼2× 10⁴ in minor fractions of the Murray meteorite¹, we found that these fractions contain two minerals not previously seen in meteorites: silicon carbide and an amorphous Si–O phase², possibly an alteration product of another silicon-bearing mineral. Here we report ion microprobe analyses of these phases which reveal very large isotopic anomalies in silicon, nitrogen and carbon, exceeding the highest anomalies previously measured by factors of up to ˜50. We conclude that these phases are circumstellar grains from carbon-rich stars, whose chemical inertness allowed them to survive in exceptionally well-preserved form.