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arXiv · 2602.20806

Characteristics of natural remanence records in fine-grained particles returned from asteroid Ryugu

Masahiko Sato·Yuki Kimura·Tadahiro Hatakeyama·Tomoki Nakamura·Satoshi Okuzumi·Sei-ichiro Watanabe·Seiji Sugita·Satoshi Tanaka·Shogo Tachibana·Hisayoshi Yurimoto·Takaaki Noguchi·Ryuji Okazaki·Hikaru Yabuta·Hiroshi Naraoka·Kanako Sakamoto·Toru Yada·Masahiro Nishimura·Aiko Nakato·Akiko Miyazaki·Kasumi Yogata·Masanao Abe·Tatsuaki Okada·Tomohiro Usui·Makoto Yoshikawa·Takanao Saiki·Fuyuto Terui·Satoru Nakazawa·Yuichi Tsuda
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Abstract

Particles collected from the asteroid Ryugu by the Hayabusa2 spacecraft offer a unique opportunity to investigate the magnetic record of the primitive solar system, as any terrestrial magnetic contamination is minimal and can be accounted for. In previous studies, stepwise alternating field demagnetization (AFD) measurements of natural remanent magnetization (NRM) records have been conducted on seven Ryugu particles. However, due to the limited number of samples, there is no consensus regarding the interpretation of the results of these measurements. To address this problem, we performed stepwise AFD measurements of the NRM on 28 Ryugu particles. Twenty-three of the particles exhibited one or two stable NRM components, whereas the remaining five did not. Isothermal remanent magnetization-based paleointensity values derived from stable NRM components varied by more than one order of magnitude. These NRM characteristics were consistent with those observed in previous studies. Therefore, as a reflection of the original nature of the NRM record, some Ryugu particles exhibited stable NRM components, whereas others did not. The Ryugu particles investigated in this study and those from a previous study exhibited spatially inhomogeneous NRM directions within individual particles, constraining the NRM acquisition time to before the final solidification of the current Ryugu particles. A mechanism of remanence acquisition that can explain the observed NRM characteristics is a chemical remanent magnetization associated with the growth of framboidal magnetite during aqueous alteration in Ryugu's parent body.

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Masahiko Sato, Yuki Kimura, Tadahiro Hatakeyama, Tomoki Nakamura, Satoshi Okuzumi, Sei-ichiro Watanabe, Seiji Sugita, Satoshi Tanaka, Shogo Tachibana, Hisayoshi Yurimoto, Takaaki Noguchi, Ryuji Okazaki, Hikaru Yabuta, Hiroshi Naraoka, Kanako Sakamoto, Toru Yada, Masahiro Nishimura, Aiko Nakato, Akiko Miyazaki, Kasumi Yogata, Masanao Abe, Tatsuaki Okada, Tomohiro Usui, Makoto Yoshikawa, Takanao Saiki, Fuyuto Terui, Satoru Nakazawa, Yuichi Tsuda. 2026-02-24. Characteristics of natural remanence records in fine-grained particles returned from asteroid Ryugu. https://doi.org/10.1029/2025je009265

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