Early fluid activity on Ryugu inferred by isotopic analyses of carbonates and magnetite

McCain, Kaitlyn A.; Matsuda, Nozomi; Liu, Ming-Chang; McKeegan, Kevin D.; Yamaguchi, Akira; Kimura, Makoto; Tomioka, Naotaka; Ito, Motoo; Imae, Naoya; Uesugi, Masayuki; Shirai, Naoki; Ohigashi, Takuji; Greenwood, Richard C.; Uesugi, Kentaro; Nakato, Aiko; Yogata, Kasumi; Yuzawa, Hayato; Kodama, Yu; Hirahara, Kaori; Sakurai, Ikuya; Okada, Ikuo; Karouji, Yuzuru; Nakazawa, Satoru; Okada, Tatsuaki; Saiki, Takanao; Tanaka, Satoshi; Terui, Fuyuto; Yoshikawa, Makoto; Miyazaki, Akiko; Nishimura, Masahiro; Yada, Toru; Abe, Masanao; Usui, Tomohiro; Watanabe, Sei-ichiro and Tsuda, Yuichi (2023). Early fluid activity on Ryugu inferred by isotopic analyses of carbonates and magnetite. Nature Astronomy, 7(3) pp. 309–317.

DOI: https://doi.org/10.1038/s41550-022-01863-0

Abstract

Samples from asteroid Ryugu returned by the Hayabusa2 mission contain evidence of extensive alteration by aqueous fluids and appear related to the CI chondrites. To understand the sources of the fluid and the timing of chemical reactions occurring during the alteration processes, we investigated the oxygen, carbon and ⁵³Mn^–53Cr systematics of carbonate and magnetite in two Ryugu particles. We find that the fluid was initially between 0 and 20 °C and enriched in ¹³C, ¹⁷O and ¹⁸O, and subsequently evolved towards lighter carbon and oxygen isotopic compositions as alteration proceeded. Carbonate ages show that this fluid–rock interaction took place within approximately the first 1.8 million years of Solar System history, requiring early accretion either in a planetesimal less than ∼20 km in diameter or within a larger body that was disrupted and reassembled.

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