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American Astronomical Society, Astrophysical Journal Letters, 1(935), p. L3, 2022

DOI: 10.3847/2041-8213/ac83bd

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Presolar Stardust in Asteroid Ryugu

Journal article published in 2022 by Jens Barosch ORCID, Larry R. Nittler ORCID, Jianhua Wang ORCID, Conel M. O.-’.-D. Alexander ORCID, Bradley T. De Gregorio ORCID, Cécile Engrand ORCID, Yoko Kebukawa ORCID, Kazuhide Nagashima ORCID, Rhonda M. Stroud ORCID, Hikaru Yabuta ORCID, Yoshinari Abe, Jérôme Aléon, Sachiko Amari ORCID, Yuri Amelin, Ken-Ichi Bajo and other authors.
This paper is made freely available by the publisher.
This paper is made freely available by the publisher.

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Abstract

Abstract We have conducted a NanoSIMS-based search for presolar material in samples recently returned from C-type asteroid Ryugu as part of JAXA's Hayabusa2 mission. We report the detection of all major presolar grain types with O- and C-anomalous isotopic compositions typically identified in carbonaceous chondrite meteorites: 1 silicate, 1 oxide, 1 O-anomalous supernova grain of ambiguous phase, 38 SiC, and 16 carbonaceous grains. At least two of the carbonaceous grains are presolar graphites, whereas several grains with moderate C isotopic anomalies are probably organics. The presolar silicate was located in a clast with a less altered lithology than the typical extensively aqueously altered Ryugu matrix. The matrix-normalized presolar grain abundances in Ryugu are 4.8 − 2.6 + 4.7 ppm for O-anomalous grains, 25 − 5 + 6 ppm for SiC grains, and 11 − 3 + 5 ppm for carbonaceous grains. Ryugu is isotopically and petrologically similar to carbonaceous Ivuna-type (CI) chondrites. To compare the in situ presolar grain abundances of Ryugu with CI chondrites, we also mapped Ivuna and Orgueil samples and found a total of 15 SiC grains and 6 carbonaceous grains. No O-anomalous grains were detected. The matrix-normalized presolar grain abundances in the CI chondrites are similar to those in Ryugu: 23 − 6 + 7 ppm SiC and 9.0 − 3.6 + 5.4 ppm carbonaceous grains. Thus, our results provide further evidence in support of the Ryugu–CI connection. They also reveal intriguing hints of small-scale heterogeneities in the Ryugu samples, such as locally distinct degrees of alteration that allowed the preservation of delicate presolar material.