Frank J. Stadermann

TL;DR: In this article, the authors reported data on 48 O-anomalous grains that were identified in grain size separates of the ungrouped carbonaceous chondrite Acfer 094.

TL;DR: In this paper, a nanoSIMS C, N and O ion imaging study of the CO3.0 chondrite ALHA77307 was carried out, and the results showed that the distribution of O-anomalous grains is similar to that observed in other primitive meteorites, and is dominated by 17 O-rich Group 1 grains from low-mass asymptotic giant branch (AGB) stars of close-to-solar metallicity.

TL;DR: In this paper, the authors investigated the origin of the deuterium and 15N isotopic anomalies in the stratosphere and found that the bulk of the N-bearing material may have obtained its isotopic signatures from low temperature chemistry, but a nucleosynthetic origin is also possible.

Abstract: Wecarriedouthypervelocityimpactexperimentsinordertotestthepossibilitythatpresolargrainsarepreferentially destroyed during impact of the comet 81P/Wild 2 samples into the Stardust Al foil collectors. Powdered samples of the ungrouped carbonaceous chondrite Acfer 094 were shot at 6 km s −1 into Stardust flight spare Al foil. Craters from the Acfer 094 test shots, as well as ones from the actual Stardust cometary foils, were analyzed by NanoSIMS ion imaging to search for presolar grains. We found two O-rich presolar grains and two presolar SiC grains in the Acfer 94 test shots, with measured abundances in the foils of 4 and 5 ppm, respectively, significantly lower than the amount of presolar grains actually present in this meteorite. Based on known abundances of these phases in Acfer 094, we estimate a loss of over 90% of the O-rich presolar grains; the fraction of SiC lost is lower, reflecting its higher resistance to destruction. In the Stardust cometary foils, we identified four O-rich presolar grains in 5000 μm 2 of crater residue. Including a presolar silicate grain found by Leitner et al., the overall measured abundance of O-rich presolar grains in Wild 2 is ∼35 ppm. No presolar SiC has been found in the foil searches, although one was identified in the aerogel samples. Based on the known abundances of presolar silicates and oxides in Acfer 094, we can calculate the pre-impact abundances of these grains in the Stardust samples. Our calculations indicate initial abundances of 600‐830 ppm for O-rich presolar grains. Assuming a typical diameter of ∼300 nm for SiC suggests a presolar SiC abundance of ∼45 ppm. Analyses of the Stardust samples indicated early on that recognizable presolar components were not particularly abundant, an observation that was contrary to expectations that the cometary material would, like interplanetary dust particles, be dominated by primitive materials from the early solar system (including abundant presolar grains), which had remained essentially unaltered over solar system history in the cold environment of the Kuiper Belt. Our work shows that comet Wild 2, in fact, does contain more presolar grains than measurements on the Stardust samples suggest, with abundances similar to those observed in primitive IDPs.

TL;DR: In this paper, the authors reported the discovery of a unique Fe-and O-bearing circumstellar grain from the Acfer 094 ungrouped carbonaceous chondrite, which has a close-to-solar 17O/16O ratio and an 18O/ 16O ratio that is 1.34 times the solar value.