Irradiation history of itokawa regolith material deduced from noble gases in the hayabusa samples

Keisuke Nagao*, Ryuji Okazaki, Tomoki Nakamura, Yayoi N. Miura, Takahito Osawa, Ken Ichi Bajo, Shintaro Matsuda, Mitsuru Ebihara, Trevor R. Ireland, Fumio Kitajima, Hiroshi Naraoka, Takaaki Noguchi, Akira Tsuchiyama, Hisayoshi Yurimoto, Michael E. Zolensky, Masayuki Uesugi, Kei Shirai, Masanao Abe, Toru Yada, Yukihiro IshibashiAkio Fujimura, Toshifumi Mukai, Munetaka Ueno, Tatsuaki Okada, Makoto Yoshikawa, Junichiro Kawaguchi

*Corresponding author for this work

    Research output: Contribution to journalArticlepeer-review

    122 Citations (Scopus)


    Noble gas isotopes were measured in three rocky grains from asteroid Itokawa to elucidate a history of irradiation from cosmic rays and solar wind on its surface. Large amounts of solar helium (He), neon (Ne), and argon (Ar) trapped in various depths in the grains were observed, which can be explained by multiple implantations of solar wind particles into the grains, combined with preferential He loss caused by frictional wear of space-weathered rims on the grains. Short residence time of less than 8 million years was implied for the grains by an estimate on cosmic-ray-produced 21Ne. Our results suggest that Itokawa is continuously losing its surface materials into space at a rate of tens of centimeters per million years. The lifetime of Itokawa should be much shorter than the age of our solar system.

    Original languageEnglish
    Pages (from-to)1128-1131
    Number of pages4
    Issue number6046
    Publication statusPublished - 26 Aug 2011


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