Sulfur four isotope NanoSIMS analysis of comet-81P/Wild 2 dust in impact craters on aluminum foil C2037N from NASA's Stardust mission

Abstract

We present NanoSIMS four-isotope S analyses of 24 comet Wild 2 dust impact residues in craters on aluminum foil C2037N returned by NASA's Stardust mission. Except for one sample, all impact residues have normal S isotopic compositions within 2σ uncertainties of at least two S isotope ratios. This implies that most S-rich Wild 2 dust impactors formed in the solar system. Instrumental isotope fractionation due to sample topography is the main contribution to our analytical uncertainty. One impact crater residue shows small anomalies of δ 33S=-57±17‰, and δ 34S=-41±17‰ (1σ uncertainties). Although this could be simply a statistical outlier or the fingerprint of a chemical isotope fractionation it is also possible that the observed anomaly results from the mixture of a cometary FeS particle with a small (150nm diam.) presolar FeS supernova grain. This would translate into a presolar sulfide abundance of approximately 200ppm. © 2012 The Meteoritical Society.