小惑星リュウグウでみつかった窒化した鉄の鉱物

　太陽から遠く離れた場所で生まれた氷天体や彗星にはアンモニウム塩のような窒素化合物が大量に貯蔵されています。このような窒素を含む固体は生命の材料物質としてとても重要だと考えられていますが、地球軌道の地域に輸送される証拠は見つかっていませんでした。本研究では、地球の近くに軌道をもつ小惑星リュウグウの砂を電子顕微鏡で調べ、砂のごく表面が窒化した鉄(窒化鉄：Fe4N)に覆われていることを発見しました。窒化鉄は、磁鉄鉱と呼ばれる鉄原子と酸素原子の鉱物の表面で見られます。我々は、氷天体からやってきたアンモニア化合物を大量に含む微小な隕石がリュウグウに衝突して、磁鉄鉱の表面で化学反応が起こり、この窒化鉄が形成したと考えました。小惑星の表層では、太陽から吹くイオンの風(太陽風)の照射などによって磁鉄鉱の表面から酸素が失われていて、アンモニアと反応しやすい金属鉄がごく表面に形成しています。このため、磁鉄鉱の表面ではアンモニアに由来する窒化鉄の合成が促されたと推測しています。この微小隕石は太陽系遠方の氷天体からやってきたかもしれず、これまで気づかれてきたよりも多くの量の窒素化合物が太陽系の地球付近に輸送されて、生命の材料となった可能性があります。
　本成果は、京都大学白眉センターの松本徹 特定助教、理学研究科の野口高明教授、三宅亮准教授、伊神洋平助教、化学研究所の治田充貴准教授、および国際的な共同研究者のグループによって行われ、2023年11月30日に英国の国際学術誌「Nature Astronomy」にオンライン掲載されました。

• 本研究の詳細についてはこちら

タイトル：Influx of nitrogen-rich material from the outer Solar System indicated by iron nitride in Ryugu samples.（太陽系遠方から運ばれた窒素に富む塵の流入を示唆する、小惑星リュウグウの表面で見つかった窒化鉄）

著　　者：Toru Matsumoto1,2*,Takaaki Noguchi2, Akira Miyake2, Yohei Igami2, Mitsutaka Haruta3, Yusuke Seto4, Masaaki Miyahara5, Naotaka Tomioka6, Hikaru Saito7,8, Satoshi Hata9,10, Dennis Harries11, Aki Takigawa12, Yusuke Nakauchi13, Shogo Tachibana14, Tomoki Nakamura15, Megumi Matsumoto15, Hope A. Ishii16, John P. Bradley16, Kenta Ohtaki16, Elena Dobrică16, Hugues Leroux17, Corentin Le Guillou17, Damien Jacob17, Francisco de la Peña17, Sylvain Laforet17, Maya Marinova18, Falko Langenhorst19, Pierre Beck20, Thi H. V. Phan20, Rolando Rebois20, Neyda M. Abreu21, Jennifer Gray22, Thomas Zega23, Pierre-M. Zanetta23, Michelle S. Thompson24, Rhonda Stroud25, Kate Burgess26, Brittany A. Cymes26, John C. Bridges27, Leon Hicks27, Martin R. Lee28, Luke Daly28,29,30, Phil A. Bland31, Michael E. Zolensky32, David R. Frank16, James Martinez33, Akira Tsuchiyama34,35,36, Masahiro Yasutake37, Junya Matsuno35, Shota Okumura2, Itaru Mitsukawa2, Kentaro Uesugi37, Masayuki Uesugi37, Akihisa Takeuchi37, Mingqi Sun35,36,38, Satomi Enju39, Tatsuhiro Michikami40, Hisayoshi Yurimoto41, Ryuji Okazaki42, Hikaru Yabuta5, Hiroshi Naraoka43, Kanako Sakamoto13, Toru Yada13, Masahiro Nishimura13, Aiko Nakato13, Akiko Miyazaki44, Kasumi Yogata13, Masanao Abe13,45, Tatsuaki Okada13,45, Tomohiro Usui13,45, Makoto Yoshikawa13,45, Takanao Saiki13,45, Satoshi Tanaka13,45, Fuyuto Terui46, Satoru Nakazawa13,45, Sei-ichiro Watanabe47, Yuichi Tsuda13,45

1The Hakubi Center for Advanced Research, Kyoto University, Kyoto, Japan. 2Division of Earth and Planetary Sciences, Kyoto University, Kyoto, Japan. 3Institute for Chemical Research, Kyoto University, Uji, Japan. 4Department of Geosciences, Osaka Metropolitan University, Osaka, Japan. 5Earth and Planetary Systems Science Program, Hiroshima University, Higashi-Hiroshima, Japan. 6Kochi Institute for Core Sample Research, X-Star, JAMSTEC, Nankoku, Japan. 7Institute for Materials Chemistry and Engineering, Kyushu University, Fukuoka, Japan. 8Pan-Omics Data-Driven Research Innovation Center, Kyushu University, Fukuoka, Japan. 9Department of Advanced Materials Science, Kyushu University, Fukuoka, Japan. 10The Ultramicroscopy Research Center, Kyushu University, Fukuoka, Japan. 11Luxembourg Institute of Science and Technology, European Space Resources Innovation Centre, Belvaux, Luxembourg. 12Department of Earth and Planetary Science, University of Tokyo, Tokyo, Japan. 13Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency, Sagamihara, Japan. 14UTokyo Organization for Planetary and Space Science, University of Tokyo, Tokyo, Japan. 15Department of Earth Science, Graduate School of Science, Tohoku University, Sendai, Japan. 16Hawai’i Institute of Geophysics & Planetology, the University of Hawai’i at Mānoa, Honolulu, HI, USA. 17Université de Lille, CNRS, INRAE; Centrale Lille, UMR 8207-UMET-Unité Matériaux et Transformations, Lille, France. 18Université de Lille, CNRS, INRAE; Centrale Lille, Université Artois, FR 2638-IMEC-Institut Michel-Eugène Chevreul, Lille, France. 19Institute of Geoscience, Friedrich Schiller University Jena, Jena, Germany. 20Institut de Planétologie et d’Astrophysique de Grenoble (IPAG), Université Grenoble Alpes, Grenoble, France. 21Langley Research Center, NASA, Hampton, VA, USA. 22Materials Characterization Lab, The Pennsylvania State University, University Park, PA, USA. 23Lunar and Planetary Laboratory, Department of Planetary Sciences, University of Arizona, Tucson, AZ, USA. 24Department of Earth, Atmospheric and Planetary Sciences, Purdue University, West Lafayette, IN, USA. 25Buseck Center for Meteorite Studies, Arizona State University, Tempe, AZ, USA. 26U.S. Naval Research Laboratory, Washington, DC, USA. 27Jacobs, NASA Johnson Space Center, Houston, TX, USA. 28Space Research Centre, University of Leicester, Leicester, UK. 29School of Geographical and Earth Sciences, University of Glasgow, Glasgow, UK. 30Australian Centre for Microscopy and Microanalysis, University of Sydney, Sydney, New South Wales, Australia. 31Department of Materials, University of Oxford, Oxford, UK. 32School of Earth and Planetary Sciences, Curtin University, Perth, Western Australia, Australia. 33ARES, NASA, Johnson Space Center, Houston, TX, USA. 34Jacobs Engineering, Dallas, TX, USA. 35Research Organization of Science and Technology, Ritsumeikan University, Kusatsu, Japan. 36CAS Key Laboratory of Mineralogy and Metallogeny/Guangdong Provincial Key Laboratory of Mineral Physics and Materials, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences (CAS), Guangzhou, China. 37CAS Center for Excellence in Deep Earth Science, Guangzhou, China. 38Japan Synchrotron Radiation Research Institute, Sayō, Japan. 39University of Chinese Academy of Sciences, Beijing, China. 40Department of Mathematics, Physics, and Earth Science, Ehime University, Matsuyama, Japan. 41Faculty of Engineering, Kindai University, Higashi-Hiroshima, Japan. 42Department of Earth and Planetary Sciences, Hokkaido University, Sapporo, Japan. 43Department of Earth and Planetary Sciences, Kyushu University, Fukuoka, Japan. 44Marine Works Japan Ltd., Yokosuka, Japan. 45The Graduate University for Advanced Studies, SOKENDAI, Hayama, Japan. 46Department of Mechanical Engineering, Kanagawa Institute of Technology, Atsugi, Japan. 47Department of Earth and Environmental Sciences, Nagoya University, Nagoya, Japan.

掲 載 誌：Nature Astronomy
DOI：10.1038/s41550-023-02137-z

理学研究院　奈良岡 浩　教授