Breunnerite grain and magnesium isotope chemistry reveal cation partitioning during aqueous alteration of asteroid Ryugu

Returned samples from the carbonaceous asteroid (162173) Ryugu provide pristine information on the original aqueous alteration history of the Solar System. Secondary precipitates, such as carbonates and phyllosilicates, reveal elemental partitioning of the major component ions linked to the primordial brine composition of the asteroid. Here, we report on the elemental partitioning and Mg isotopic composition (<sup>25</sup>Mg/<sup>24</sup>Mg) of breunnerite [(Mg, Fe, Mn)CO<sub>3</sub>] from the Ryugu C0002 sample and the A0106 and C0107 aggregates by sequential leaching extraction of salts, exchangeable ions, carbonates, and silicates. Breunnerite was the sample most enriched in light Mg isotopes, and the <sup>25</sup>Mg/<sup>24</sup>Mg value of the fluid had shifted lower by ~0.38‰ than the initial value (set to 0‰) before dolomite precipitation. As a simple model, the Mg<sup>2+</sup> first precipitated in phyllosilicates, followed by dolomite precipitation, at which time ~76-87% of Mg<sup>2+</sup> had been removed from the primordial brine. A minor amount of phyllosilicate precipitation continued after dolomite precipitation. The element composition profiles of the latest solution that interacted with the cation exchange pool of Ryugu were predominantly Na-rich. Na<sup>+</sup> acts as a bulk electrolyte and contributes to the stabilization of the negative surface charge of phyllosilicates and organic matter on Ryugu.

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Journal
Nature Communications
Published
2024-09-05
DOI
https://doi.org/10.1038/s41467-024-50814-y
Citations
11
Primary Topic
Astro and Planetary Science
Type
article
Field-Weighted Citation Impact
3.65

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article

Breunnerite grain and magnesium isotope chemistry reveal cation partitioning during aqueous alteration of asteroid Ryugu

Toshiki Koga, Yoshinori Takano, Takanao Saiki, Daisuke Araoka et al.
11 citations
Nature Communications
Astro and Planetary Science
3.65
article

Breunnerite grain and magnesium isotope chemistry reveal cation partitioning during aqueous alteration of asteroid Ryugu

Toshiki Koga, Yoshinori Takano, Takanao Saiki, Daisuke Araoka, Masahiro Nishimura, Kanako Sakamoto, Naohiko Ohkouchi, Sei‐ichiro Watanabe, Nanako O. Ogawa, Shogo Tachibana, Satoru Tanaka, Martin Bizzarro, Aiko Nakato, Makoto Yoshikawa, Tomoki Nakamura, Tatsuaki Okada, Masanao Abe, Tetsuya Yokoyama, Tomohiro Usui, Hikaru Yabuta, Hisayoshi Yurimoto, Fuyuto Terui, Toshihiro Yoshimura, Satoru Nakazawa, Saburo Sakai, R. OKAZAKI, T. Noguchi, Akiko Miyazaki, Kasumi Yogata, Jason P. Dworkin, Morihiko Onose, Satoshi Tanaka, Toru Yada, Hiroshi Naraoka, Mayu Morita, Yuichi Tsuda
article en
11 citations

Abstract

Returned samples from the carbonaceous asteroid (162173) Ryugu provide pristine information on the original aqueous alteration history of the Solar System. Secondary precipitates, such as carbonates and phyllosilicates, reveal elemental partitioning of the major component ions linked to the primordial brine composition of the asteroid. Here, we report on the elemental partitioning and Mg isotopic composition (<sup>25</sup>Mg/<sup>24</sup>Mg) of breunnerite [(Mg, Fe, Mn)CO<sub>3</sub>] from the Ryugu C0002 sample and the A0106 and C0107 aggregates by sequential leaching extraction of salts, exchangeable ions, carbonates, and silicates. Breunnerite was the sample most enriched in light Mg isotopes, and the <sup>25</sup>Mg/<sup>24</sup>Mg value of the fluid had shifted lower by ~0.38‰ than the initial value (set to 0‰) before dolomite precipitation. As a simple model, the Mg<sup>2+</sup> first precipitated in phyllosilicates, followed by dolomite precipitation, at which time ~76-87% of Mg<sup>2+</sup> had been removed from the primordial brine. A minor amount of phyllosilicate precipitation continued after dolomite precipitation. The element composition profiles of the latest solution that interacted with the cation exchange pool of Ryugu were predominantly Na-rich. Na<sup>+</sup> acts as a bulk electrolyte and contributes to the stabilization of the negative surface charge of phyllosilicates and organic matter on Ryugu.

Nature CommunicationsVol. 15(1)
Hiroshima University (JP), Tokyo Institute of Technology (JP), University of Copenhagen (DK), Goddard Space Flight Center (US), Japan Agency for Marine-Earth Science and Technology (JP), Kyushu University (JP), Horiba (Japan) (JP), Kanagawa Institute of Technology (JP), Tohoku University (JP), Hokkaido University (JP), Kyoto University (JP), Japan Aerospace Exploration Agency (JP), Geological Survey of Japan (JP), Institute of Space and Astronautical Science (JP), Nagoya University (JP), National Institute of Advanced Industrial Science and Technology (JP), The University of Tokyo (JP)
National Aeronautics and Space Administration, National Institute of Advanced Industrial Science and Technology, Centre National d’Etudes Spatiales, University of Tokyo, Hokkaido University, Goddard Space Flight Center, Japan Society for the Promotion of Science, Japan Agency for Marine-Earth Science and Technology, Japan Aerospace Exploration Agency, Institute of Space and Astronautical Science
Life below water
Openalex Percentile: Top 7%
Astro and Planetary Science
3.65
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