The Inventory of Presolar Grains in Primitive Meteorites: A NanoSIMS Study of C-, N-, and O-isotopes in NWA 852

Abstract

Meteorites as well as interplanetary and cometary dust contain small amounts of mineral grains that formed in the winds of evolved stars or in the ejecta of stellar explosions and survived incorporation into solid bodies of our own solar system. Investigation of the abundance and distribution of these “presolar grains” in primitive solar system matter can shed light on parent body processes as well as possible heterogeneities in the early solar nebula. We investigated presolar silicate and oxide grains in the CR chondrite NWA 852 with a NanoSIMS 50. Abundances of 77 ppm for silicates, 39 ppm for oxides, and 160 ppm for silicon carbide, as well as evidence for N-enriched organic molecular cloud material were observed. Although NWA 852 has the lowest presolar silicate/oxide-ratio observed so far for presolar-grain-rich material, indicating extensive aqueous alteration, a significant fraction of O-anomalous grains (silicates and oxides) remained intact. Thus, this meteorite may be a link between presolargrain-rich, pristine CR chondrites and CRs with lower presolar grain abundances.