The Magnesium Isotope Composition of Samples Returned from Asteroid Ryugu

Titelangaben

Bizzarro, Martin ; Schiller, Martin ; Yokoyama, Tetsuya ; Abe, Yoshinari ; Aléon, Jérôme ; Alexander, Conel M. O’D. ; Amari, Sachiko ; Amelin, Yuri ; Bajo, Ken-ichi ; Bouvier, Audrey ; Carlson, Richard W. ; Chaussidon, Marc ; Choi, Byeon-Gak ; Dauphas, Nicolas ; Davis, Andrew M. ; Di Rocco, Tommaso ; Fujiya, Wataru ; Fukai, Ryota ; Gautam, Ikshu ; Haba, Makiko K. ; Hibiya, Yuki ; Hidaka, Hiroshi ; Homma, Hisashi ; Hoppe, Peter ; Huss, Gary R. ; Ichida, Kiyohiro ; Iizuka, Tsuyoshi ; Ireland, Trevor R. ; Ishikawa, Akira ; Itoh, Shoichi ; Kawasaki, Noriyuki ; Kita, Noriko T. ; Kitajima, Kouki ; Kleine, Thorsten ; Komatani, Shintaro ; Krot, Alexander N. ; Liu, Ming-Chang ; Masuda, Yuki ; Morita, Mayu ; Moynier, Fréderic ; Motomura, Kazuko ; Nakai, Izumi ; Nagashima, Kazuhide ; Nesvorný, David ; Nguyen, Ann ; Nittler, Larry ; Onose, Morihiko ; Pack, Andreas ; Park, Changkun ; Piani, Laurette ; Qin, Liping ; Russell, Sara S. ; Sakamoto, Naoya ; Schönbächler, Maria ; 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:
The Magnesium Isotope Composition of Samples Returned from Asteroid Ryugu.
In: The Astrophysical Journal Letters. Bd. 958 (2023) Heft 2 . - L25.
ISSN 2041-8213
DOI: https://doi.org/10.3847/2041-8213/ad09d9

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Abstract

The nucleosynthetic isotope composition of planetary materials provides a record of the heterogeneous distribution of stardust within the early solar system. In 2020 December, the Japan Aerospace Exploration Agency Hayabusa2 spacecraft returned to Earth the first samples of a primitive asteroid, namely, the Cb-type asteroid Ryugu. This provides a unique opportunity to explore the kinship between primitive asteroids and carbonaceous chondrites. We report high-precision μ 26Mg* and μ 25Mg values of Ryugu samples together with those of CI, CM, CV, and ungrouped carbonaceous chondrites. The stable Mg isotope composition of Ryugu aliquots defines μ 25Mg values ranging from –160 ± 20 ppm to –272 ± 30 ppm, which extends to lighter compositions relative to Ivuna-type (CI) and other carbonaceous chondrite groups. We interpret the μ 25Mg variability as reflecting heterogeneous sampling of a carbonate phase hosting isotopically light Mg (μ 25Mg ∼ –1400 ppm) formed by low temperature equilibrium processes. After correcting for this effect, Ryugu samples return homogeneous μ 26Mg* values corresponding to a weighted mean of 7.1 ± 0.8 ppm. Thus, Ryugu defines a μ 26Mg* excess relative to the CI and CR chondrite reservoirs corresponding to 3.8 ± 1.1 and 11.9 ± 0.8 ppm, respectively. These variations cannot be accounted for by in situ decay of 26Al given their respective 27Al/24Mg ratios. Instead, it requires that Ryugu and the CI and CR parent bodies formed from material with a different initial 26Al/27Al ratio or that they are sourced from material with distinct Mg isotope compositions. Thus, our new Mg isotope data challenge the notion that Ryugu and CI chondrites share a common nucleosynthetic heritage.