The Inventory of Stardust Grains in the Solar Nebula - Implications from Isotopic and Petrologic Studies of Primitive Solar System Materials

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Primitive meteorites, interplanetary dust particles, and samples from comet 81P/Wild 2 contain small quantities of refractory dust grains that are older than our Solar System and which formed in the winds of evolved stars or in the ejecta of stellar explosions. These presolar (stardust) grains can be identified on the basis of large isotopic anomalies with respect to average Solar System matter. Their abundances vary among different primitive Solar System materials, apparently reflecting processes of secondary alteration (e.g., aqueous alteration or thermal heating) and possibly also heterogeneities in the solar nebula. Here, we will continue to investigate the presolar grain inventories of CR clan chondrites, which are amongst the most primitive meteorites known, by NanoSIMS ion imaging. The matrix petrology in these meteorites will be studied in detail by optical microscopy and electron microprobe and compared with the presolar grain inventory to investigate the effects of thermal and aqueous alteration, genetic relationships and formation scenarios for CR clan chondrites, and to infer constraints on the presolar grain abundance in the solar nebula. We will also continue to study matter from comet Wild 2, returned by NASA’s STARDUST mission, in order to explore the currently not well determined presolar grain abundance in matter from this pristine Solar System body. These studies will be complemented by a search for and possible chemical and isotopic studies of residues in impact craters in Al foils from STARDUST’s interstellar dust collector.