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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：43 Percentile：96.93(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.
Kitazato, Kohei*; Milliken, R. E.*; Iwata, Takahiro*; Abe, Masanao*; Otake, Makiko*; Matsuura, Shuji*; Arai, Takehiko*; Nakauchi, Yusuke*; Nakamura, Tomoki*; Matsuoka, Moe*; et al.
Science, 364(6437), p.272 - 275, 2019/04
Times Cited Count：259 Percentile：99.73(Multidisciplinary Sciences)The near-Earth asteroid 162173 Ryugu, the target of Hayabusa2 sample return mission, is believed to be a primitive carbonaceous object. The Near Infrared Spectrometer (NIRS3) on Hayabusa2 acquired reflectance spectra of Ryugu's surface to provide direct measurements of the surface composition and geological context for the returned samples. A weak, narrow absorption feature centered at 2.72 micron was detected across the entire observed surface, indicating that hydroxyl (OH)-bearing minerals are ubiquitous there. The intensity of the OH feature and low albedo are similar to thermally- and/or shock-metamorphosed carbonaceous chondrite meteorites. There are few variations in the OH-band position, consistent with Ryugu being a compositionally homogeneous rubble-pile object generated from impact fragments of an undifferentiated aqueously altered parent body.
Inaba, Satoru*; Anabuki, Takuya*; Shirai, Kazutaka*; Yabana, Shuichi*; Kitamura, Seiji
Proceedings of 2009 ASME Pressure Vessels and Piping Division Conference (PVP 2009) (CD-ROM), 8 Pages, 2009/07
Suzuki, Yoshiyuki*; Yoshida, Yukari*; Shirai, Katsuyuki*; Hamada, Nobuyuki*; Mizui, Toshiyuki*; Noda, Shinei*; Funayama, Tomoo; Sakashita, Tetsuya; Kobayashi, Yasuhiko; Shirao, Tomoaki*; et al.
JAEA-Review 2006-042, JAEA Takasaki Annual Report 2005, P. 107, 2007/02
Tobita, Kenji; Nishitani, Takeo; Harano, Hideki*; Tani, Keiji; Isobe, Mitsutaka*; Fujita, Takaaki; Kusama, Yoshinori; G.A.Wurden*; Shirai, Hiroshi; Oikawa, Toshihiro; et al.
Fusion Energy 1996, Vol.1, p.497 - 505, 1997/00
no abstracts in English
Tobita, Kenji; Harano, Hideki*; Nishitani, Takeo; Fujita, Takaaki; Tani, Keiji; Oikawa, Toshihiro; Shirai, Hiroshi; Kusama, Yoshinori
Nuclear Fusion, 37(11), p.1583 - 1592, 1997/00
Times Cited Count：26 Percentile：64.72(Physics, Fluids & Plasmas)no abstracts in English
Shirai, Hiroshi; Takizuka, Tomonori; Kikuchi, Mitsuru; Mori, Masahiro; Nishitani, Takeo; Ishida, Shinichi; Kamada, Yutaka; Sato, Masayasu; Isei, Nobuaki; Koide, Yoshihiko; et al.
IAEA-CN-60/A2-17, 0, p.355 - 364, 1995/00
no abstracts in English
Shirai, Eiji
Oyo Butsuri, 64(9), p.927 - 928, 1995/00
no abstracts in English
Onishi, Nobuaki; Shirai, Eiji
Proc. of the 9th Pacific Basin Nuclear Conf., Vol. 2, p.1071 - 1076, 1994/00
no abstracts in English
Funahashi, Satoru; Shirai, Eiji; Morii, Yukio; Kodaira, Tsuneo; Takahashi, Hidetake
Nihon Genshiryoku Gakkai-Shi, 35(9), p.809 - 811, 1993/09
no abstracts in English
12, 1993, Mito, JapanFunahashi, Satoru; Shirai, Eiji; Morii, Yukio; Kodaira, Tsuneo; Takahashi, Hidetake
Journal of Nuclear Science and Technology, 30(8), p.837 - 842, 1993/08
no abstracts in English
Shirai, Hiroshi; Hirayama, Toshio; Shimizu, Katsuhiro; Tani, Keiji; Azumi, Masafumi; Hirai, Kenichiro*; Konno, Satoshi*; Takase, Keizo*
JAERI-M 93-026, 97 Pages, 1993/02
no abstracts in English
Shirai, Eiji; Saito, Minoru; Tanaka, Toshiyuki
Genshiryoku Kogyo, 39(11), p.10 - 17, 1993/00
no abstracts in English
Shirai, Eiji; Soyama, Kazuhiko
Genshiryoku Kogyo, 39(11), p.48 - 53, 1993/00
no abstracts in English
Matsubayashi, Masahito; Tsuruno, Akira; Ichikawa, Hiroki; Kodaira, Tsuneo; Shirai, Eiji
Proceedings of 4th Asian Symposium on Research Reactors (ASRR-4), p.192 - 197, 1993/00
no abstracts in English
Isshiki, Masahiko; Takahashi, Hidetake; Ichikawa, Hiroki; Shirai, Eiji
Nihon Genshiryoku Gakkai-Shi, 34(2), p.108 - 118, 1992/02
Times Cited Count：5 Percentile：48.18(Nuclear Science & Technology)no abstracts in English
Shirai, Eiji; ; Kodaira, Tsuneo; Sato, Hiroshi
Proc. of the 3rd Int. Conf. on Nuclear Fuel Reprocessing and Waste Management: RECOD91,Vol. l, p.367 - 370, 1991/00
no abstracts in English
Shirai, Eiji; Aoyama, Isao
Genshiryoku Kogyo, 35(12), p.41 - 50, 1989/12
no abstracts in English
Shimizu, Katsuhiro; Hirayama, Toshio; Shirai, Hiroshi; Tani, Keiji; *; Azumi, Masafumi
JAERI-M 89-146, 53 Pages, 1989/10
no abstracts in English
Aoyama, Isao; Shirai, Eiji;
50 Years with Nuclear Fission, p.843 - 848, 1989/00
no abstracts in English
