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Article Dans Une Revue Earth and Planetary Science Letters Année : 2024

Microscale hydrogen, carbon, and nitrogen isotopic diversity of organic matter in asteroid Ryugu

Katherine Burgess
  • Fonction : Auteur
Jianhua Wang
Shohei Yamashita
  • Fonction : Auteur
Yoshio Takahashi
  • Fonction : Auteur
Alexandre Dazzi
Bradley de Gregorio
Ariane Deniset-Besseau
Mutsumi Komatsu
Gilles Montagnac
Scott Sandford
Yasuo Takeichi
  • Fonction : Auteur
Takaaki Noguchi
Sei-Ichiro Watanabe

Résumé

We report the H, C, and N isotopic compositions of microscale (0.2 to 2 µm) organic matter in samples of asteroid Ryugu and the Orgueil CI carbonaceous chondrite. Three regolith particles of asteroid Ryugu, returned by the Hayabusa2 spacecraft, and several fragments of Orgueil were analyzed by NanoSIMS isotopic imaging. The isotopic distributions of the Ryugu samples from two different collection spots are closely similar to each other and to the Orgueil samples, strengthening the proposed Ryugu-CI chondrite connection. Most individual sub-μm organic grains have isotopic compositions within error of bulk values, but 2–10 % of them are outliers exhibiting large isotopic enrichments or depletions in D, 15N, and/or 13C. The H, C and N isotopic compositions of the outliers are not correlated with each other: while some organic grains are both D- and 15N-enriched, many are enriched or depleted in one or the other system. This most likely points to a diversity in isotopic fractionation pathways and thus diversity in the local formation environments for the individual outlier grains. The observation of a relatively small population of isotopic outlier grains can be explained either by escape from nebular and/or parent body homogenization of carbonaceous precursor material or addition of later isotopic outlier grains. The strong chemical similarity of isotopically typical and isotopically outlying grains, as reflected by synchrotron x-ray absorption spectra, suggests a genetic connection and thus favors the former, homogenization scenario. However, the fact that even the least altered meteorites show the same pattern of a small population of outliers on top of a larger population of homogenized grains indicates that some or most of the homogenization occurred prior to accretion of the macromolecular organic grains into asteroidal parent bodies.
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hal-04587649 , version 1 (01-06-2024)

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Larry Nittler, Jens Barosch, Katherine Burgess, Rhonda Stroud, Jianhua Wang, et al.. Microscale hydrogen, carbon, and nitrogen isotopic diversity of organic matter in asteroid Ryugu. Earth and Planetary Science Letters, 2024, 637, pp.118719. ⟨10.1016/j.epsl.2024.118719⟩. ⟨hal-04587649⟩
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