Zinc, copper and calcium isotopic composition of Ryugu’s samples
Frédéric Moynier1, Marine Paquet1, Wei Dai1, Tetsuya Yokoyama2, Yan Hu1, The Hayabusa2-initialanalysis chemistry team, The Hayabusa2-initial-analysis core.
1
Université Paris Cité, Institut de physique du globe de Paris, CNRS; 75005 Paris, France
2

Department of Earth and Planetary Sciences, Tokyo Institute of Technology; Tokyo 152-8551, Japan.

In December 2020, the JAXA Hayabusa2 spacecraft returned to Earth with the first samples collected from a Cb-typeasteroid, (162173) Ryugu [1,2]. Initial analyses showed that Ryugu’s composition is close to that of the CI (Ivunalike) carbonaceous chondrite group [3,4], the chemically most primitive meteorites characterized by near-solar
abundances for most elements. Some isotopic signatures (Ti, Cr) of Ryugu overlap, however, with other carbonaceouschondrite (CC) groups. Zinc (Zn) and copper (Cu) are moderately volatile elements (MVE) that display variable
isotopic compositions across the different chondrite groups and could be used to further test the Ryugu/CI connection.
Furthermore, one notable chemical difference between Ryugu and CI chondrites is an apparent excess of over 50%
Ca in the former that may be related to a heterogeneous distribution of carbonates (dolomite and calcite) [3,5]. Given
that calcium in carbonates can be isotopically fractionated during aqueous alteration and carbonate precipitation,
leading to more than 1‰ variations in the 44Ca/40Ca ratio in terrestrial carbonates, it could be a useful tool forinvestigating the origin of the Ca excesses in the Ryugu samples compared to CI. In addition, Ca exhibits large isotopic
variations among bulk carbonaceous chondrites (CC), with the 44Ca/40Ca ratio range also spanning a range of 1 ‰,and therefore, Ca stable isotopes could be used to further test the Ryugu/CI connection.
Here we will present the first stable isotopic composition of Zn, Cu, [6] and Ca [7] from two Ryugu sampling sites.
We show that Ryugu and CI chondrites have identical Zn and Cu isotopic compositions, demonstrating their common
genetic heritage and ruling out any affinity with other groups of CC. Since Ryugu’s pristine samples match the solar
elemental composition for many elements, their Zn and Cu isotopic compositions likely represent the best estimatesof the proto-solar composition. Earth’s mass-independent Zn isotopic composition is intermediate between Ryugu/CCand non-carbonaceous chondrites, suggesting a contribution of Ryugu-like material to Earth’s budgets of Zn and otherMVE. We also show that both Ryugu samples have similar Ca isotopic composition that falls within the range definedby CIs, notwithstanding their higher Ca contents. This similarity likely indicates that the Ca isotopic composition andthe Ca budget of CIs and Ryugu samples are dominated by carbonates and consistent with a major event involving
precipitation of carbonates in the Ryugu samples that has been dated by 53Mn-53Cr chronology to have occurred ~5Ma
after Solar System formation.

The Hayabusa2-initial-analysis chemistry team: K. Nagashima, I. Nakai, E.D. Young, Y. Abe, J. Aléon, C.M.O'D.
Alexander, S. Amari, Y. Amelin, K. Bajo, M. Bizzarro, A. Bouvier, R. W. Carlson, M. Chaussidon, B.-G. Choi, N.
Dauphas, A. M. Davis, T. Di Rocco, W. Fujiya, R. Fukai, I. Gautam, M. K. Haba, Y. Hibiya, H. Hidaka, H. Homma,P. Hoppe, G.R. Huss, K. Ichida, T. Iizuka, T.R. Ireland, A. Ishikawa, M. Ito, S. Itoh, N. Kawasaki, N. T. Kita, K.
Kitajima, T. Kleine, S. Komatani, A. N. Krot, M.-C. Liu, Yuki Masuda, K.D. McKeegan, M. Morita, K. Motomura,A. Nguyen, L. Nittler, M. Onose, A. Pack, C. Park, L. Piani, L. Qin, S.S. Russell, N. Sakamoto, M. Schönbächler, L.
Tafla, H. Tang, K. Terada, Y. Terada, T. Usui, S. Wada, M. Wadhwa, R.J. Walker, K. Yamashita, Q.-Z. Yin, S.
Yoneda, H. Yui, A.-C. Zhang, H. Yurimoto.
The Hayabusa2-initial-analysis core: S. Tachibana, T. Nakamura, H. Naraoka, T. Noguchi, R. Okazaki, K.
Sakamoto, H. Yabuta, H. Yurimoto, Y. Tsuda, S. Watanabe.

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01550-6 (2022). [3] Yokoyama, T. et al. The first returned samples from a C-type asteroid show kinship to thechemically most primitive meteorites. Science 10.1126/science.abn7850 (2022). [4] Nakamura, E., K., K., Tanaka,R., Kunihiro, T. & Kitagawa, H. On the origin and evolution of the asteroid Ryugu: A comprehensive geochemicalperspective. Proc. Jpn. Acad., Ser. B 6, 227-282 (2022). [5] Nakamura, T. et al. Science (accepted).[6] Paquet et al.
Copper and Zinc Isotopic Fingerprints of the Contribution of Ryugu-like Material to Earth’s Volatile Inventory.
Nature Astronomy (in revision). [7] Moynier et al. The Solar System calcium isotopic composition inferred fromRyugu samples. Geochemical Perspective Letters (accepted).