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Solar system calcium isotopic composition deduced from Ryugu samples

Less than two years after the Japanese Hayabusa2 mission returned samples from asteroid Ryugu to Earth, new international studies are refining the preliminary results. In a study published in October in the journal Geochemical Perspectives Letters, a team of cosmochemists from IPGP use state-of-the-art instrumentation to analyze the calcium isotopic composition of these samples. The study shows that this isotopic composition is close to that of CI chondrites, enabling us to retrace part of the history of asteroid Ryugu.

Solar system calcium isotopic composition deduced from Ryugu samples

Publication date: 07/11/2022

General public, Press, Research

Related themes : Origins

In December 2020, the Japanese probe Hayabusa2 brought back to Earth 5g of samples from the asteroid Ryugu. Preliminary analyses carried out by an international team, including researchers from the IPGP, had shown that these fragments have a chemical composition that is generally very close to that of Ivuna-type carbonaceous chondrites, the most primitive meteorites and considered to have the composition closest to the Sun. With one exception, however: these asteroid samples are greatly enriched in calcium compared with Ivuna-type chondrites.

Sample of asteroid (162173) Ryugu (© ISAS/JAXA)

To understand this excess of calcium, a new study has been carried out at the IPGP, again in collaboration with the international preliminary sample study team, to analyse the isotopic abundance of calcium in the Ryugu samples. Isotopic abundances retain a signature of the origin of elements, and their measurements are used in cosmochemistry to understand the processes that have affected elemental abundances.

Thanks to its plasma source mass spectrometer equipped with a collision cell (financed in 2021 with the help of the Île de France region’s major areas of interest programme), the first instrument of this type to be installed in France, the IPGP is currently the only laboratory in the world capable of carrying out ultra-precise measurements of calcium isotopic composition on minute quantities of samples.

The team at the institute responsible for these measurements has shown that the calcium isotopic signature of the Ryugu samples is similar to that of Ivuna-type meteorites, and can therefore be traced back to the initial calcium isotopic signature of the solar system. The study also shows that the calcium enrichment initially measured was due to an excess of carbonate minerals in the Ryugu samples. The formation of these carbonate minerals coincides with a major episode of aqueous alteration on the Ryugu asteroid ~5 million years after the formation of the solar system, i.e. more than 4560 million years ago.

Ref : Moynier, F., Dai, W., Yokoyama, T., Hu, Y., Paquet, M., Abe, Y., Aléon, J., Alexander, C.M.O’D., Amari, S., Amelin, Y., Bajo, K.-I., Bizzarro, M., Bouvier, A., Carlson, R.W., Chaussidon, M., Choi, B.-G., Dauphas, N., Davis, A.M., Di Rocco, T., Fujiya, W., Fukai, R., Gautam, I., Haba, M.K., Hibiya, Y., Hidaka, H., Homma, H., Hoppe, P., Huss, G.R., Ichida, K., Iizuka, T., Ireland, T.R., Ishikawa, A., Ito, M., Itoh, S., Kawasaki, N., Kita, N.T., Kitajima, K., Kleine, T., Komatani, S., Krot, A.N., Liu, M.-C., Masuda, Y., McKeegan, K.D., Morita, M., Motomura, K., Nakai, I., Nagashima, K., Nesvorný, D., Nguyen, A., Nittler, L., Onose, M., Pack, A., Park, C., Piani, L., Qin, L., Russell, S.S., Sakamoto, N., Schönbächler, M., Tafla, L., Tang, H., Terada, K., Terada, Y., Usui, T., Wada, S., Wadhwa, M., Walker, R.J., Yamashita, K., Yin, Q.-Z., Yoneda, S., Young, E.D., Yui, H., Zhang, A.-C., Nakamura, T., Naraoka, H., Noguchi, T., Okazaki, R., Sakamoto, K., Yabuta, H., Abe, M., Miyazaki, A., Nakato, A., Nishimura, M., Okada, T., Yada, T., Yogata, K., Nakazawa, S., Saiki, T., Tanaka, S., Terui, F., Tsuda, Y., Watanabe, S.-I., Yoshikawa, M., Tachibana, S., Yurimoto, H. (2022) The Solar System calcium isotopic composition inferred from Ryugu samples. Geochem. Persp. Let. 24, 1-6. https://doi.org/10.7185/geochemlet.2238

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