The Distribution and Inventory of Stardust Grains in Primitive Solar System Materials: Implications from Isotopic, Elemental and Petrologic Studies of Meteorites and Cometary Dust

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Primitive meteorites, interplanetary dust and cometary material contain small concentrations of so-called presolar or stardust grains. These mineral grains, which formed in the winds of evolved stars or in the ejecta of nova and supernova explosions, are older than our Solar System and were subsequently incorporated into the molecular cloud from which our Solar System formed some 4.6 billion years ago. Presolar grains can be distinguished from solids that formed in the Solar System by their highly anomalous isotopic compositions with respect to average Solar System material. Their concentrations vary among different primitive Solar System materials, apparently reflecting metamorphic processes on the parent bodies and possibly also heterogeneities in the solar nebula. Here, I will investigate the presolar grain inventories different reservoirs of fine-grained material (fine-grained dust rims and interchondrule matrix) in CR and CM chondrites, which are amongst the most primitive meteorites, by NanoSIMS ion imaging. The petrology and elemental composition of the fine-grained portions of these meteorites will be studied in detail by scanning electron microscopy (SEM), SEM-based energy-dispersive x-ray spectroscopy (SEM-EDS), and electron microprobe and compared with the respective presolar grain inventories. This allows to investigate the effects of thermal and aqueous alteration and formation scenarios for CR and CM chondrites, and to determine constraints on the presolar grain abundance in formation regions of the CR and CM chondrites within the solar nebula. I will also conduct a study of material from comet 81P/Wild 2, returned by NASAs STARDUST mission, in order to explore the currently still not well determined presolar grain abundance in matter from this pristine Solar System body. Impact craters of cometary dust will be identified in Al foils from the STARDUST cometary dust collector by SEM. The residual matter will be characterized by SEM-EDS, and the presolar grain inventory will be analyzed by NanoSIMS ion imaging.