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Kitazato, Kohei*; Milliken, R. E.*; Iwata, Takahiro*; Abe, Masanao*; Otake, Makiko*; Matsuura, Shuji*; Takagi, Yasuhiko*; Nakamura, Tomoki*; Hiroi, Takahiro*; Matsuoka, Moe*; et al.
Nature Astronomy (Internet), 5(3), p.246 - 250, 2021/03
Times Cited Count：49 Percentile：96.63(Astronomy & Astrophysics)Here we report observations of Ryugu's subsurface material by the Near-Infrared Spectrometer (NIRS3) on the Hayabusa2 spacecraft. Reflectance spectra of excavated material exhibit a hydroxyl (OH) absorption feature that is slightly stronger and peak-shifted compared with that observed for the surface, indicating that space weathering and/or radiative heating have caused subtle spectral changes in the uppermost surface. However, the strength and shape of the OH feature still suggests that the subsurface material experienced heating above 300 
C, similar to the surface. In contrast, thermophysical modeling indicates that radiative heating does not increase the temperature above 200 C at the estimated excavation depth of 1 m, even if the semimajor axis is reduced to 0.344 au. This supports the hypothesis that primary thermal alteration occurred due to radiogenic and/or impact heating on Ryugu's parent body.
Yokobori, Shinichi*; Yang, Y.*; Sugino, Tomohiro*; Kawaguchi, Yuko*; Itahashi, Shiho*; Fujisaki, Kenta*; Fushimi, Hidehiko*; Hasegawa, Sunao*; Hashimoto, Hirofumi*; Hayashi, Nobuhiro*; et al.
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Kobayashi, Kensei*; Mita, Hajime*; Nakashima, Satoru*; Yabuta, Hikaru*; Yokobori, Shinichi*; Narumi, Issei; Naganuma, Takeshi*
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Kobayashi, Kensei*; Kawamoto, Yukinori*; Sarker, P. K.*; Ono, Keisuke*; Kuwahara, Hideharu*; Obayashi, Yumiko*; Kaneko, Takeo*; Mita, Hajime*; Yabuta, Hikaru*; Yoshida, Satoshi*; et al.
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Kobayashi, Kensei*; Kawamoto, Yukinori*; Sarker, P. K.*; Kuwahara, Hideharu*; Obayashi, Yumiko*; Kaneko, Takeo*; Mita, Hajime*; Yabuta, Hikaru*; Yoshida, Satoshi*; Narumi, Issei; et al.
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Yokobori, Shinichi*; Kawaguchi, Yuko*; Yang, Y.*; Kawashiri, Narutoshi*; Shiraishi, Keisuke*; Shimizu, Yasuyuki*; Takahashi, Yuta*; Sugino, Tomohiro*; Narumi, Issei; Sato, Katsuya; et al.
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Yokobori, Shinichi*; Kawaguchi, Yuko*; Yang, Y.*; Kawashiri, Narutoshi*; Shiraishi, Keisuke*; Shimizu, Yasuyuki*; Takahashi, Yuta*; Sugino, Tomohiro*; Narumi, Issei; Sato, Katsuya; et al.
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Yokobori, Shinichi*; Kawaguchi, Yuko*; Shimizu, Yasuyuki*; Kawashiri, Narutoshi*; Shiraishi, Keisuke*; Sugino, Tomohiro*; Takahashi, Yuta*; Yang, Y.*; Tanigawa, Yoshiaki*; Hashimoto, Hirofumi*; et al.
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Yokobori, Shinichi*; Kawaguchi, Yuko*; Harada, Miyu*; Murano, Yuka*; Tomita, Kaori*; Hayashi, Nobuhiro*; Tabata, Makoto*; Kawai, Hideyuki*; Okudaira, Kyoko*; Imai, Eiichi*; et al.
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Yokobori, Shinichi*; Yang, Y.*; Kawaguchi, Yuko*; Sugino, Tomohiro*; Takahashi, Yuta*; Narumi, Issei; Takahashi, Yuichi*; Hayashi, Nobuhiro*; Yoshimura, Yoshitaka*; Tabata, Makoto*; et al.
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Yamagishi, Akihiko*; Yokobori, Shinichi*; Hashimoto, Hirofumi*; Yano, Hajime*; Imai, Eiichi*; Okudaira, Kyoko*; Kawai, Hideyuki*; Kobayashi, Kensei*; Tabata, Makoto*; Nakagawa, Kazumichi*; et al.
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Yokobori, Shinichi*; Hashimoto, Hirofumi*; Hayashi, Nobuhiro*; Imai, Eiichi*; Kawai, Hideyuki*; Kobayashi, Kensei*; Mita, Hajime*; Nakagawa, Kazumichi*; Narumi, Issei; Okudaira, Kyoko*; et al.
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Yokobori, Shinichi*; Kobayashi, Kensei*; Mita, Hajime*; Yabuta, Hikaru*; Nakagawa, Kazumichi*; Narumi, Issei; Hayashi, Nobuhiro*; Tomita, Kaori*; Kawaguchi, Yuko*; Shimizu, Yasuyuki*; et al.
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Osawa, Takahito; Ninomiya, Kazuhiko*; Nakamura, Tomoki*; Takahashi, Tadayuki*; Terada, Kentaro*; Yurimoto, Hisayoshi*; Noguchi, Takaaki*; Okazaki, Ryuji*; Yabuta, Hikaru*; Naraoka, Hiroshi*; et al.
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I report on the muonic X-ray analysis experiment conducted at J-PARC from 2020 to 2021, in which the analytical method was significantly developed through four preliminary experiments and successfully analyzed samples from the asteroid Ryugyu in July 2021. The experimental process is described from a radiochemical point of view.
