Nucleosynthetic s-Process Depletion in Mo from Ryugu samples returned by Hayabusa2
Noriyoshi Nakanishi, Tetsuya Yokoyama, A. Ishikawa, R.J. Walker, Yoshinari Abe, J. Aléon, C. M. O'd. Alexander, S. Amari, Yuri Amelin, Ken‐ichi Bajo, Martin Bizzarro, Audrey Bouvier, Richard W. Carlson, Marc Chaussidon, Byeon‐Gak Choi, Nicolas Dauphas, A. M. Davis, Tommaso Di Rocco, Wataru Fujiya, Ryota Fukai, Ikshu Gautam, Makiko K. Haba, Yuki Hibiya, Hiroshi Hidaka, Hisashi Homma, P. Höppe, G. R. Huss, Kiyohiro Ichida, Tsuyoshi Iizuka, T. R. Ireland, Shoichi Itoh, Noriyuki Kawasaki, N. T. Kita, Kouki Kitajima, T. Kleine, Shintaro Komatani, Alexander N. Krot, M.-C. Liu, Yuki Masuda, Masato Morita, K. Motomura, Frédéric Moynier, Izumi Nakai, K. Nagashima, A. N. Nguyen, L. R. Nittler, Morihiko Onose, Andreas Pack, Changkun Park, Laurette Piani, Liping Qin, S. S. Russell, Naoya Sakamoto, Maria Schönbächler, Lauren Tafla, Haolan Tang, Kentaro Terada, Yasuko Terada, Tomohiro Usui, Sohei Wada, M. Wadhwa, K. Yamashita, Qing‐Zhu Yin, Shigekazu Yoneda, Edward Young, Hiroharu Yui, A.-C. Zhang, Tomoki Nakamura, H. Naraoka, T. Noguchi, Ryuji Okazaki, K. Sakamoto, H. Yabuta, Masanao Abe, Akiko Miyazaki, Aiko Nakato, M. Nishimura, Tatsuaki Okada, Toru Yada, Kasumi Yogata, Satoru Nakazawa, Takanao Saiki, Satoshi Tanaka, Fuyuto Terui, Yuichi Tsuda, Sei‐ichiro Watanabe, Makoto Yoshikawa, Shogo Tachibana, Hisayoshi Yurimoto
Abstract
Initial analyses of samples collected from two locations on the asteroid Ryugu indicated that the mineralogical, chemical, and isotopic characteristics of the Ryugu samples show similarities to carbonaceous chondrites, particularly the Ivuna-type (CI) group. In this study, we analysed a composite sample of four bulk Ryugu samples (A0106, A0106-A0107, C0107, and C0108) collected from both sampling locations that were combined in order to determine its mass independent Mo isotopic composition and reveal contributions from diverse nucleosynthetic sources. The ɛ94Mo and ɛ95Mo values for the Ryugu sample are characterised by the carbonaceous chondrite (CC)-type, which is consistent with the nucleosynthetic isotope compositions observed for other elements (Cr, Ti, Fe, and Zn). The Ryugu composite sample, however, is characterised by greater s-process depletion of Mo isotopes compared with any known bulk carbonaceous chondrite, even including CI chondrites. The observed Mo isotopic signature in the Ryugu composite was most likely caused by either incomplete digestion of s-process-rich presolar SiC, or biased sampling of materials enriched in aqueously-formed secondary minerals characterised by s-process-poor Mo isotopes, resulting from the physicochemical separation between s-process-rich presolar grains and a complementary s-process-poor aqueous fluid in the Ryugu parent body.