研究者業績
基本情報
- 所属
- 国立研究開発法人宇宙航空研究開発機構 宇宙科学研究所 太陽系科学研究系 助教東京大学 大学院理学系研究科 地球惑星科学専攻 助教
- 学位
- 理学博士(名古屋大学)理学修士(名古屋大学)
- 連絡先
- hayakawa
planeta.sci.isas.jaxa.jp - J-GLOBAL ID
- 200901009402364446
- researchmap会員ID
- 1000363026
経歴
3-
2007年9月 - 現在
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2003年10月 - 2007年8月
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1990年3月 - 2003年9月
学歴
2-
- 1989年
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- 1984年
論文
62-
Advances in Space Research 2024年5月
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Communications Earth & Environment 4(1) 2023年9月27日 査読有りAbstract Returned samples from Cb-type asteroid (162173) Ryugu exhibit very dark spectra in visible and near-infrared ranges, generally consistent with the Hayabusa2 observations. A critical difference is that a structural water absorption of hydrous silicates is around twice as deep in the returned samples compared with those of Ryugu’s surface, suggesting Ryugu surface is more dehydrated. Here we use laboratory experiments data to indicate the spectral differences between returned samples and asteroid surface are best explained if Ryugu surface has (1) higher porosity, (2) larger particle size, and (3) more space-weathered condition, with the last being the most effective. On Ryugu, space weathering by micrometeoroid bombardments promoting dehydration seem to be more effective than that by solar-wind implantation. Extremely homogeneous spectra of the Ryugu’s global surface is in contrast with the heterogeneous S-type asteroid (25143) Itokawa’s spectra, which suggests space weathering has proceeded more rapidly on Cb-type asteroids than S-type asteroids.
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Earth, Planets and Space 75(1) 2023年8月22日 査読有りAbstract Zodiacal light (ZL) is sunlight scattered by interplanetary dust particles (IDPs) at optical wavelengths. The spatial distribution of IDPs in the Solar System may hold an important key to understanding the evolution of the Solar System and material transportation within it. The number density of IDPs can be expressed as $$n(r) \sim r^{-\alpha }$$, and the exponent $$\alpha \sim 1.3$$ was obtained by previous observations from interplanetary space by Helios 1/2 and Pioneer 10/11 in the 1970s and 1980s. However, no direct measurements of $$\alpha $$ based on ZL observations from interplanetary space outside Earth’s orbit have been performed since then. Here, we introduce initial results for the radial profile of the ZL at optical wavelengths observed over the range 0.76$$-$$1.06 au by ONC-T aboard the Hayabusa2# mission in 2021-2022. The ZL brightness we obtained is well reproduced by a model brightness, although there is a small excess of the observed ZL brightness over the model brightness at around 0.9 au. The radial power-law index we obtained is $$\alpha = 1.30 \pm 0.08$$, which is consistent with previous results based on ZL observations. The dominant source of uncertainty arises from the uncertainty in estimating the diffuse Galactic light (DGL). Graphical Abstract
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Earth, Planets and Space 75(1) 2023年3月13日 査読有りAfter delivering its sample capsule to Earth, the Hayabusa2 spacecraft started its extended mission to perform a flyby of asteroid 2001 CC21 in 2026 and rendezvous with asteroid 1998 KY26 in 2031. During the extended mission, the optical navigation camera (ONC) of Hayabusa2 will play an important role in navigation and science observations, but it has suffered from optical deterioration after the spacecraft's surface contact with and sampling of asteroid Ryugu. Furthermore, the sensitivity of the telescopic camera (ONC-T) has continued to decrease for more than a year, posing a serious problem for the extended mission. These are problems that could potentially be encountered by other sample-return missions involving surface contact. In this study, we evaluated the long-term variation of ONC performance over the 6.5 years following the launch in 2014 to predict how it will perform during observations of the two target asteroids in its extended mission (6 and 11 years from the Earth return, respectively). Our results showed several important long-term trends in ONC performance, such as transmission, dark noise level, and hot pixels. During the long cruising period of the extended mission, we plan to observe both zodiacal light and exoplanet transits as additional science targets. The accuracy of these observations is sensitive to background noise level and stray-light contamination, so we conducted new test observations to search for the lowest stray light, which has been found to depend on spacecraft attitude. The results of these analyses and new test observations suggest that the Hayabusa2 ONC will be able to conduct cruising, flyby, and rendezvous observations of asteroids with sufficient accuracy.
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Science 379(6634) 2023年2月24日 査読有りSamples of the carbonaceous asteroid (162173) Ryugu were collected and brought to Earth by the Hayabusa2 spacecraft. We investigated the macromolecular organic matter in Ryugu samples and found that it contains aromatic and aliphatic carbon, ketone, and carboxyl functional groups. The spectroscopic features of the organic matter are consistent with those in chemically primitive carbonaceous chondrite meteorites that experienced parent-body aqueous alteration (reactions with liquid water). The morphology of the organic carbon includes nanoglobules and diffuse carbon associated with phyllosilicate and carbonate minerals. Deuterium and/or nitrogen-15 enrichments indicate that the organic matter formed in a cold molecular cloud or the presolar nebula. The diversity of the organic matter indicates variable levels of aqueous alteration on Ryugu’s parent body.
MISC
55書籍等出版物
2-
Primitive Solar Nebula and Origin of the Planets(Terra Publication Press) 1993年
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Primitive Solar Nebula and Origin of the Planets(Terra Publication Press) 1993年
講演・口頭発表等
217-
52nd LPSC 2021年3月18日
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JpGU-AGU Joint Meeting 2020 2020年7月15日
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JpGU-AGU Joint Meeting 2020 2020年7月15日
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JpGU-AGU Joint Meeting 2020 2020年7月15日
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JpGU-AGU Joint Meeting 2020 2020年7月15日
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JpGU-AGU Joint Meeting 2020 2020年7月15日 招待有り
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JpGU-AGU Joint Meeting 2020 2020年7月15日
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JpGU-AGU Joint Meeting 020 2020年7月15日 招待有り
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Seismic wave propagation on asteroid Ryugu induced by the impact experiment of the Hayabusa2 missionJpGU-AGU Joint Meeting 2020 2020年7月15日
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JpGU-AGU Joint Meeting 2020 2020年7月14日
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JpGU-AGU Joint Meeting 2020 2020年7月14日
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JpGU-AGU Joint Meeting 2020 2020年7月14日
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51st LPSC 2020年3月17日
所属学協会
3-
2009年 - 現在
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1992年 - 現在
Works(作品等)
6共同研究・競争的資金等の研究課題
10-
日本学術振興会 科学研究費助成事業 基盤研究(A) 2015年4月 - 2018年3月
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日本学術振興会 科学研究費助成事業 2000年 - 2002年
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日本学術振興会 科学研究費助成事業 1997年 - 1998年
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日本学術振興会 科学研究費助成事業 1992年 - 1993年
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1984年 - 1990年
