研究者業績
基本情報
経歴
1-
2023年5月 - 現在
論文
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Science (New York, N.Y.) 379(6634) eabo0431 2023年2月24日The near-Earth carbonaceous asteroid (162173) Ryugu is expected to contain volatile chemical species that could provide information on the origin of Earth's volatiles. Samples of Ryugu were retrieved by the Hayabusa2 spacecraft. We measured noble gas and nitrogen isotopes in Ryugu samples and found that they are dominated by presolar and primordial components, incorporated during Solar System formation. Noble gas concentrations are higher than those in Ivuna-type carbonaceous (CI) chondrite meteorites. Several host phases of isotopically distinct nitrogen have different abundances among the samples. Our measurements support a close relationship between Ryugu and CI chondrites. Noble gases produced by galactic cosmic rays, indicating a ~5 million year exposure, and from implanted solar wind record the recent irradiation history of Ryugu after it migrated to its current orbit.
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Science (New York, N.Y.) 379(6634) eabn9033 2023年2月24日The Hayabusa2 spacecraft collected samples from the surface of the carbonaceous near-Earth asteroid (162173) Ryugu and brought them to Earth. The samples were expected to contain organic molecules, which record processes that occurred in the early Solar System. We analyzed organic molecules extracted from the Ryugu surface samples. We identified a variety of molecules containing the atoms CHNOS, formed by methylation, hydration, hydroxylation, and sulfurization reactions. Amino acids, aliphatic amines, carboxylic acids, polycyclic aromatic hydrocarbons, and nitrogen-heterocyclic compounds were detected, which had properties consistent with an abiotic origin. These compounds likely arose from an aqueous reaction on Ryugu's parent body and are similar to the organics in Ivuna-type meteorites. These molecules can survive on the surfaces of asteroids and be transported throughout the Solar System.
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Science Advances 8(46) 2022年11月The Hayabusa2 spacecraft returned to Earth from the asteroid 162173 Ryugu on 6 December 2020. One day after the recovery, the gas species retained in the sample container were extracted and measured on-site and stored in gas collection bottles. The container gas consists of helium and neon with an extraterrestrial 3He/4He and 20Ne/22Ne ratios, along with some contaminant terrestrial atmospheric gases. A mixture of solar and Earth’s atmospheric gas is the best explanation for the container gas composition. Fragmentation of Ryugu grains within the sample container is discussed on the basis of the estimated amount of indigenous He and the size distribution of the recovered Ryugu grains. This is the first successful return of gas species from a near-Earth asteroid.
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Monthly Notices of the Royal Astronomical Society 514(4) 6173-6182 2022年8月1日The JAXA Hayabusa2 mission accomplished the formation of an artificial crater on the asteroid Ryugu. The aim of this work is to analyse the area surrounding the artificial crater and reveal spectral variability compared to the same region before the crater formation, to mineralogically and physically characterize the subsurface exposed material. The crater's investigation focused on the analysis of two regions corresponding to the inner part of crater (the pit and the crater wall/floor), two areas related to ejecta deposited close to the crater, two areas of ejecta moved far from the crater, and two external areas. Each area was investigated both before and after the crater formation, by the study of the photometrically corrected spectral parameters: the 1.9 μm reflectance, the near-infrared spectral slope, and the depth of the bands at 2.7 and 2.8 μm. The subsurface material of the post-crater areas shows deeper absorption bands, a decrease in reflectance, and a reddening in spectral slope with respect to the surface material of pre-crater areas. The subsurface regolith could have experienced a lower OH devolatilization due to space weathering and/or could be composed of finer dark grains than the surface layer. The ejecta reached distances of ~20 m from the impact point, mainly moving in the northern direction; nevertheless, a few ejecta also reached the south-eastern part of crater.
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Planetary and Space Science 219 105519-105519 2022年6月 査読有り
MISC
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Earth, Planets and Space 70(1) 2018年12月1日© 2018, The Author(s). The ultraviolet imager (UVI) has been developed for the Akatsuki spacecraft (Venus Climate Orbiter mission). The UVI takes ultraviolet (UV) images of the solar radiation reflected by the Venusian clouds with narrow bandpass filters centered at the 283 and 365 nm wavelengths. There are absorption bands of SO2and unknown absorbers in these wavelength regions. The UV images provide the spatial distribution of SO2and the unknown absorber around cloud top altitudes. The images also allow us to understand the cloud top morphologies and haze properties. Nominal sequential images with 2-h intervals are used to understand the dynamics of the Venusian atmosphere by estimating the wind vectors at the cloud top altitude, as well as the mass transportation of UV absorbers. The UVI is equipped with off-axial catadioptric optics, two bandpass filters, a diffuser installed in a filter wheel moving with a step motor, and a high sensitivity charge-coupled device with UV coating. The UVI images have spatial resolutions ranging from 200 m to 86 km at sub-spacecraft points. The UVI has been kept in good condition during the extended interplanetary cruise by carefully designed operations that have maintained its temperature maintenance and avoided solar radiation damage. The images have signal-to-noise ratios of over 100 after onboard desmear processing. [Figure not available: see fulltext.].
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Earth, Planets and Space 70(1) 2018年12月1日© 2018, The Author(s). The status and initial products of the 1-μm camera onboard the Akatsuki mission to Venus are presented. After the successful retrial of Venus’ orbit insertion on Dec. 2015 (5 years after the failure in Dec. 2010), and after a long cruise under intense radiation, damage in the detector seems small and fortunately insignificant in the final quality of the images. More than 600 dayside images have been obtained since the beginning of regular operation on Apr. 2016 although nightside images are less numerous (about 150 in total at three wavelengths) due to the light scattered from the bright dayside. However, data acquisition stopped after December 07, 2016, due to malfunction of the electronics and has not been resumed since then. The 0.90-µm dayside images are of sufficient quality for the cloud-tracking procedure to retrieve wind field in the cloud region. The results appear to be similar to those reported by previous 1-μm imaging by Galileo and Venus Express. The representative altitude sampled for such dayside images is estimated to be 51–55 km. Also, the quality of the nightside 1.01-µm images is sufficient for a search for active volcanism, since interference due to cloud inhomogeneity appears to be insignificant. The quality of the 0.97-µm images may be insufficient to achieve the expected spatial resolution for the near-surface H2O mixing ratio retrievals.[Figure not available: see fulltext.].
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第50回月・惑星シンポジウム = Proceedings of the 50th ISAS Lunar and Planetary Symposium 2017年8月第50回月・惑星シンポジウム (2017年8月3-4日. 宇宙航空研究開発機構宇宙科学研究所(JAXA)(ISAS)), 相模原市, 神奈川県著者人数: 15名資料番号: SA6000200016
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Proceedings of the International Astronautical Congress, IAC 2016年1月1日Copyright © 2016 by the International Astronautical Federation (IAF). All rights reserved. Japan's Venus Climate Orbiter Akatsuki was proposed to ISAS (Institute of Space and Astronautical Science) in 2001 as an interplanetary mission. We made 5 cameras with narrow-band filters to image Venus at different wavelengths to track the cloud and minor components distribution at different heights to study the Venusian atmospheric dynamics in 3 dimension. It was launched on May 21st, 2010 and reached Venus on December 7th, 2010. With the thrust by the orbital maneuver engine, Akatsuki tried to go into the westward equatorial orbit around Venus with the 30 hours' orbital period, however it failed by the malfunction of the propulsion system. Later the spacecraft has been orbiting the sun for 5 years. On December 7th, 2015 Akatsuki met Venus again after the orbit control and Akatsuki was put into the westward equatorial orbit whose apoapsis is about 0.44 million km and orbital period of 14 days. Its main target is to shed light on the mechanism of the fast atmospheric circulation of Venus. The systematic imaging sequence by Akatsuki is advantageous for detecting meteorological phenomena with various temporal and spatial scales. We have five photometric sensors as mission instruments for imaging, which are 1 m-infrared camera (IR1), 2 m-infrared camera (IR2), ultra-violet imager (UVI), long-wave infrared camera (LIR), and lightning and airglow camera (LAC). These photometers except LIR have changeable filters in the optics to image in certain wavelengths. Akatsuki's long elliptical orbit around Venus is suitable for obtaining cloud-tracked wind vectors over a wide area continuously from high altitudes. With the observation, the characterizations of the meridional circulation, mid-latitude jets, and various wave activities are anticipated. The technical issues of Venus orbit insertion in 2015 and the scientific new results will be given in this paper.
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宇宙航空研究開発機構研究開発報告 14 184-208 2015年3月惑星探査機に搭載された観測機器の視野をシミュレートすることは,これまで多くの観測機器が行ってきたことであり,また将来的にも利用されつづける機能の1 つである.私たちは,SPICE Toolkit を利用した,汎用的な視野画像シミュレータFLOW を開発した.FLOW は2 つのコンソールプログラムから構成され,一つはシミュレーション・エンジンであり,もう一つは画像生成プログラムである.シミュレーション・エンジンは,シミュレーション結果を含んだXMLファイルを出力する.画像生成プログラムは,そのXML を読み込み,FITS/PNG/JPEG フォーマットで画像を生成する.本報告では,ユースケースに基づいた要求項目を列挙し,FLOW の持つ描画機能について説明する.またFLOW を用いたウェブブラウザベースのソフトウェアについても紹介する.
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宇宙航空研究開発機構研究開発報告 11 141-149 2012年3月JAXAの月周回衛星かぐや(SELENE)に搭載されたハイビジョンカメラ(HDTV)により,約106万枚のフレーム画像が取得されている.このHDTV画像を一般と研究者の両方に提供するために,惑星科学データの相互交換用プロトコルPDAPを採用したデータ公開システムの開発を行っている.本論文では公開システムのデザイン,データモデル,実装例について紹介する.
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宇宙航空研究開発機構研究開発報告 11 121-131 2012年3月1969年から1977年にかけてNASAのアポロミッションで得られた月地震データは地球以外の天体で得られた最初の地震記録である.このデータは,取得以来40年経った現在でも解析が続けられており月の地球物理学研究において主要な役割を果たしている.一方で,得られた月地震データセットの全てが,現在のデータ公開機関でアーカイブされ,公開されているわけではない.また,多くの公開データのフォーマットが一般の地震学で使用されるものと異なるため,現状,ユーザーが必要なデータと情報を取得し,解析研究を行うのに敷居の高さを伴っている.そこで,本研究では,これまでよりも容易にユーザーが要求する月地震データとそのメタデータを取り出し,解析に供することができるApollo月地震データ公開システムを開発した.この開発のため,まず我々はほとんど全ての月地震データのアーカイブとデータ解析に必要となる情報の収集と整理を行った.そして,デコードしたデータから構成されるリレーショナル型データベースとデータベースへアクセスするアプリケーションを開発し,Web上でユーザーが要求する月地震データを検索して取得できるようにした.本研究で開発した公開システムを通して,より多くのユーザーが月地震データにアクセスできるようになり,解析研究を通して,月惑星科学を更に進展させていくことが期待される.
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SCIENCE 333(6046) 1119-1121 2011年8月A single grain (similar to 3 micrograms) returned by the Hayabusa spacecraft was analyzed by neutron activation analysis. This grain is mainly composed of olivine with minor amounts of plagioclase, troilite, and metal. Our results establish that the Itokawa sample has similar chemical characteristics (iron/scandium and nickel/cobalt ratios) to chondrites, confirming that this grain is extraterrestrial in origin and has primitive chemical compositions. Estimated iridium/nickel and iridium/cobalt ratios for metal in the Itokawa samples are about five times lower than CI carbonaceous chondrite values. A similar depletion of iridium was observed in chondrule metals of ordinary chondrites. These metals must have condensed from the nebular where refractory siderophile elements already condensed and were segregated.
共同研究・競争的資金等の研究課題
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日本学術振興会 科学研究費助成事業 2013年4月 - 2015年3月
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日本学術振興会 科学研究費助成事業 2011年 - 2012年
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日本学術振興会 科学研究費助成事業 1999年 - 2001年
