Initial study of regolith exposure ages and burial conditions on Ryugu: Cosmogenic nuclides score in two touchdownsOPEN ACCESS 

Kunihiko Nishiizumi, Keisuke Nagao, Marc W. Caffee, Ryuji Okazaki, Jozef Masarik, Hisayoshi Yurimoto, Tomoki Nakamura, Takaaki Noguchi, Hiroshi Naraoka, Hikaru Yabuta, Kanako Sakamoto, Kasumi Yogata, Toru Yada, Shogo Tachibana, Sei-ichiro Watanabe, Yuichi Tsuda, Masanao Abe, Kazuya Kumagai, Akiko Miyazaki, Aiko Nakato, Satoru Nakazawa, Masahiro Nishimura, Tatsuaki Okada, Takanao Saiki, Hirotaka Sawada, Satoshi Tanaka, Tomohiro Usui, Koji Wada, Hajime Yano, Makoto Yoshikawa, Hayabusa2 Initial Analysis Volatile Team

MAPS, Version of Record online:23 February 2026

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“Surface processes on the asteroid Ryugu have been investigated using cosmic-ray-produced radionuclides, 10Be, 26Al, and 36Cl, and stable noble gases, on eight samples returned by the Hayabusa2 spacecraft. The 10Be and 26Al along with 21Ne measurements indicate that the two Chamber A samples A0105 collected during the first touchdown (TD) were exposed to cosmic rays for ~6.8 Myr at a shielding depth of 4–15 g cm−2. Beryllium-10 and 26Al from Chamber C samples from the second TD site, close to the artificial crater, were ejected from shielding depths of 120–160 g cm−2 for C0002, 20–85 g cm−2 for C0106-09, and 120–155 g cm−2 for C0106-10, -11, and -12, respectively. The exposure ages of these four C0106 samples differ, ranging from 1.7–8.8 Myr. These measurements provide unique and clear evidence that Hayabusa2 successfully collected subsurface samples ejected by an artificially produced crater. Chlorine-36 produced by secondary-produced thermal neutrons was observed in the samples, consistent with the high concentration of H and Cl. Helium (He) and Ne of solar wind origin were released at the lowest heating temperature of 200°C during a stepwise pyrolysis.”