Zirconium isotope composition indicates s‐process depletion in samples returned from asteroid Ryugu
Authors: Schönbächler Maria , Fehr Manuela A. , Yokoyama Tetsuya , Gautam Ikshu , Nakanishi Nao , Abe Yoshinari , Aléon Jérôme , Alexander Conel , Amari Sachiko , Amelin Yuri , Bajo Ken‐ichi , Bizzarro Martin , Bouvier Audrey , Carlson Richard W. , Chaussidon Marc , Choi Byeon‐Gak , Dauphas Nicolas , Davis Andrew M. , Di Rocco Tommaso , Fujiya Wataru , Fukai Ryota , Haba Makiko K. , Hibiya Yuki , Hidaka Hiroshi , Homma Hisashi , Hoppe Peter , Huss Gary R. , Ichida Kiyohiro , Iizuka Tsuyoshi , Ireland Trevor , Ishikawa Akira , Itoh Shoichi , Kawasaki Noriyuki , Kita Noriko T. , Kitajima Koki , Kleine Thorsten , Komatani Shintaro , Krot Alexander N. , Liu Ming‐Chang , Masuda Yuki , Morita Mayu , Motomura Kazuko , Moynier Frédéric , Nakai Izumi , Nagashima Kazuhide , Nguyen Ann , Nittler Larry , Onose Morihiko , Pack Andreas , Park Changkun , Piani Laurette , Qin Liping , Russell Sara , Sakamoto Naoya , Tafla Lauren , Tang Haolan , Terada Kentaro , Terada Yasuko , Usui Tomohiro , Wada Sohei , Wadhwa Meenakshi , Walker Richard J. , Yamashita Katsuyuki , Yin Qing‐Zhu , Yoneda Shigekazu , Young Edward D. , Yui Hiroharu , Zhang Ai‐Cheng , Nakamura Tomoki , Naraoka Hiroshi , Noguchi Takaaki , Okazaki Ryuji , Sakamoto Kanako , Yabuta Hikaru , Abe Masanao , Miyazaki Akiko , Nakato Aiko , Nishimura Masahiro , Okada Tatsuaki , Yada Toru , Yogata Kasumi , Nakazawa Satoru , Saiki Takanao , Tanaka Satoshi , Terui Fuyuto , Tsuda Yuichi , Watanabe Sei‐ichiro , Yoshikawa Makoto , Tachibana Shogo , Yurimoto Hisayoshi 
Published: November 2024

Nucleosynthetic isotope variations are powerful tracers to determine genetic relationships between meteorites and planetary bodies. They can help to link material collected by space missions to known meteorite groups. The Hayabusa 2 mission returned samples from the Cb‐type asteroid (162173) Ryugu. The mineralogical, chemical, and isotopic characteristics of these samples show strong similarities to carbonaceous chondrites and in particular CI chondrites. The nucleosynthetic isotope compositions of Ryugu overlap with CI chondrites for several elements (e.g., Cr, Ti, Fe, and Zn). In contrast to these isotopes, which are of predominately supernovae origin, s‐process variations in Mo isotope data are similar to those of carbonaceous chondrites, but even more s‐process depleted. To further constrain the origin of this depletion and test whether this signature is also present for other s‐process elements, we report Zr isotope compositions for three bulk Ryugu samples (A0106, A0106‐A0107, C0108) collected from the Hayabusa 2 mission. The data are complemented with that of terrestrial rock reference materials, eucrites, and carbonaceous chondrites. The Ryugu samples are characterized by distinct 96Zr enrichment relative to Earth, indicative of a s‐process depletion. Such depletion is also observed for carbonaceous chondrites and eucrites, in line with previous Zr isotope work, but it is more extreme in Ryugu, as observed for Mo isotopes. Since s‐process Zr and Mo are coupled in mainstream SiC grains, these distinct s‐process variations might be due to SiC grain depletion in the analyzed materials, potentially caused by incomplete sample digestion, because the Ryugu samples were dissolved on a hotplate only to avoid high blank levels for other elements (e.g., Cr). However, local depletion of SiC grains cannot be excluded. An alternative, equally possible scenario is that aqueous alteration redistributed anomalous, s‐process‐depleted, Zr on a local scale, for example, into Ca‐phosphates or phyllosilicates.