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Journal Articles

Thermally altered subsurface material of asteroid (162173) Ryugu

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:30 Percentile:96.87(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 $$^{circ}$$C, similar to the surface. In contrast, thermophysical modeling indicates that radiative heating does not increase the temperature above 200 $$^{circ}$$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.

Journal Articles

The Surface composition of asteroid 162173 Ryugu from Hayabusa2 near-infrared spectroscopy

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:233 Percentile:99.74(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.

Journal Articles

NIRS3; The Near Infrared Spectrometer on Hayabusa2

Iwata, Takahiro*; Kitazato, Kohei*; Abe, Masanao*; Otake, Makiko*; Arai, Takehiko*; Arai, Tomoko*; Hirata, Naru*; Hiroi, Takahiro*; Honda, Chikatoshi*; Imae, Naoya*; et al.

Space Science Reviews, 208(1-4), p.317 - 337, 2017/07

 Times Cited Count:49 Percentile:72.49(Astronomy & Astrophysics)

NIRS3: The Near Infrared Spectrometer is installed on the Hayabusa2 spacecraft to observe the target C-type asteroid 162173 Ryugu at near infrared wavelengths of 1.8 to 3.2 micrometer. It aims to obtain reflectance spectra in order to detect absorption bands of hydrated and hydroxide minerals in the 3 micrometer-band. We adopted a linear-image sensor with indium arsenide (InAs) photo diodes and a cooling system with a passive radiator to achieve an optics temperature of 188 K, which enables to retaining sufficient sensitivity and noise level in the 3 micrometer wavelength region. We conducted ground performance tests for the NIRS3 flight model (FM) to confirm its baseline specifications. The results imply that the properties such as the signal-to-noise ratio (SNR) conform to scientific requirements to determine the degree of aqueous alteration, such as CM or CI chondrite, and the stage of thermal metamorphism on the asteroid surface.

JAEA Reports

Information basis for developing comprehensive waste management system; US-Japan Joint Nuclear Energy Action Plan Waste Management Working Group Phase I report (Joint research)

Yui, Mikazu; Ishikawa, Hirohisa; Watanabe, Atsuo*; Yoshino, Kyoji*; Umeki, Hiroyuki; Hioki, Kazumasa; Naito, Morimasa; Seo, Toshihiro; Makino, Hitoshi; Oda, Chie; et al.

JAEA-Research 2010-015, 106 Pages, 2010/05

JAEA-Research-2010-015.pdf:13.58MB

This report summarizes the activity of Phase I of Waste Management Working Group of the United States - Japan Joint Nuclear Energy Action Plan started in 2007. The working group focused on consolidation of the existing technical basis between the U.S. and Japan and the joint development of a plan for future collaborative activities. Firstly, the political/regulatory frameworks related to nuclear fuel cycles in both countries were reviewed. The various advanced fuel cycle scenarios in both countries were surveyed and summarized. Secondly, the waste management/disposal system optimization was discussed. Repository system concepts for the various classifications of nuclear waste were reviewed and summarized, then disposal system optimization processes and techniques were reviewed, and factors to consider in future repository design optimization activities were also discussed. Finally the potential collaboration areas and activities related to the optimization problem were extracted.

JAEA Reports

Safety demonstration tests of postulated solvent fire accidents in extraction process of a fuel reprocessing plant, Part III

Takada, Junichi; Koike, Tadao; Tsukamoto, Michio; Nishio, Gunji; Kitani, Susumu*; Uno, Seiichiro; ; Watanabe, Hironori; Hashimoto, Kazuichiro

JAERI-M 92-048, 332 Pages, 1992/03

JAERI-M-92-048.pdf:5.41MB

no abstracts in English

JAEA Reports

Safety demonstration tests of postulated solvent fire accidents in extraction process of a fuel reprocessing plant, Part II

Tsukamoto, Michio; Takada, Junichi; Koike, Tadao; Nishio, Gunji; Kitani, Susumu*; Uno, Seiichiro; ; Watanabe, Hironori; Hashimoto, Kazuichiro

JAERI-M 92-047, 384 Pages, 1992/03

JAERI-M-92-047.pdf:6.91MB

no abstracts in English

JAEA Reports

Safety demonstration tests of solvent fire accidents in a fuel reprocessing plant

Takada, Junichi; Koike, Tadao; Tsukamoto, Michio; Nishio, Gunji; Kitani, Susumu*; Uno, Seiichiro; ; Watanabe, Hironori; Hashimoto, Kazuichiro

JAERI-M 91-145, 195 Pages, 1991/09

JAERI-M-91-145.pdf:3.57MB

no abstracts in English

JAEA Reports

Japanese contributions to blanket design for ITER

Kuroda, Toshimasa*; Yoshida, Hiroshi; Takatsu, Hideyuki; Seki, Yasushi; Noda, Kenji; Watanabe, H.; Koizumi, Koichi; Nishio, Satoshi; *; *; et al.

JAERI-M 91-133, 191 Pages, 1991/08

JAERI-M-91-133.pdf:5.79MB

no abstracts in English

JAEA Reports

Conceptual design study of fusion experimental reactor (FY86 FER); Reactor configuration/structure design

; ; Mizoguchi, Tadanori*; *; *; *; Watanabe, Takashi*; Mori, Seiji*; Adachi, Junichi*; *; et al.

JAERI-M 87-139, 355 Pages, 1987/09

JAERI-M-87-139.pdf:8.78MB

no abstracts in English

JAEA Reports

Conceptual design study of fusion experimental reactor (FY86 FER); Critical issues of reactor configuration/structure design

; ; Mizoguchi, Tadanori*; *; *; *; Watanabe, Takashi*; Mori, Seiji*; Adachi, Junichi*; *; et al.

JAERI-M 87-138, 155 Pages, 1987/09

JAERI-M-87-138.pdf:3.62MB

no abstracts in English

Oral presentation

Muonic X-ray analysis for Ryugu samples

Osawa, Takahito; Ninomiya, Kazuhiko*; Nakamura, Tomoki*; Takahashi, Tadayuki*; Terada, Kentaro*; Yurimoto, Hisayoshi*; Noguchi, Takaaki*; Okazaki, Ryuji*; Yabuta, Hikaru*; Naraoka, Hiroshi*; et al.

no journal, , 

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.

Oral presentation

Spectral characteristics of asteroid (162173) Ryugu with Hayabusa2 NIRS3

Takir, D.*; Kitazato, Kohei*; Milliken, R. E.*; Iwata, Takahiro*; Abe, Masanao*; Otake, Makiko*; Matsuura, Shuji*; Arai, Takehiko*; Nakauchi, Yusuke*; Nakamura, Tomoki*; et al.

no journal, , 

JAXA spacecraft and sample return mission Hayabusa2 has arrived at the near-Earth asteroid 162173 Ryugu, which is classified a primitive carbonaceous object. Here we report recent results of near-infrared spectrometer (NIRS3) on the Hayabusa2 spacecraft. The observations provide direct measurements of the surface composition of Ryugu and context for the returned samples. NIRS3 has detected a weak and narrow absorption feature centered at 2.72 micrometer across entire observed surface. This absorption feature is attributed to the presence of OH-bearing minerals. The NIRS3 observations also revealed that Ryugu is the darkest object to be observed up-close by a visiting spacecraft. The intensity of the OH feature and low albedo are consistent with thermally-and/or shock-metamorphosed, and/or carbon-rich space-weathered primitive and hydrated carbonaceous chondrites.

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