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MICHIKAMI Tatsuhiro

    Department of Mechanical Engineering　Professor
Last Updated :2024/04/25

Researcher Information

Degree

  • Evolution of Asteroid Regolith layers by Cratering（The University of Tokyo）

URL

Research funding number

  • 60369931

ORCID ID

J-Global ID

Research Interests

  • 探査機はやぶさ   レゴリス   小惑星   惑星科学   Regolith   Asteroid   Planetary Science   

Research Areas

  • Natural sciences / Solid earth science

Academic & Professional Experience

  • 2019/04 - Today  Kindai UniversityFaculty of Engineering, Faculty of Engineering教授
  • 2012/04 - 2019/03  Kindai UniversityFaculty of Engineering, Faculty of Engineering准教授
  • 2008/04 - 2012/03  Fukushima National College of Technology General Education一般教科 物理科Associate Professor
  • 2003/04 - 2008/03  National Institute of Technology, Fukushima CollegeDepartment of General Education専任講師
  • 1997/04 - 1998/03  日本貨物鉄道株式会社（JR貨物）

Education

  • 1998/04 - 2001/07  The University of Tokyo  理学系研究科  地球惑星科学専攻 博士課程
  • 1995/04 - 1997/03  Hokkaido University  理学研究科  地球惑星科学専攻 修士課程
  • 1992/10 - 1995/03  Hokkaido University  School of Science  地球物理学科
  • 1991/04 - 1992/09  Hokkaido University  理I系

Association Memberships

  • 日本惑星科学会   The Japanese Society for Planetary Science   

Published Papers

  • Tatsuhiro Michikami; Axel Hagermann; Akira Tsuchiyama; Yushi Otsuka; Michihiko Nakamura; Satoshi Okumura; Harumasa Kano; Junya Matsuno; Sunao Hasegawa
    Icarus Elsevier BV 116068 - 116068 0019-1035 2024/04 [Refereed]
  • Rhonda M. Stroud; Jens Barosch; Lydie Bonal; Katherine Burgess; George D. Cody; Bradley T. De Gregorio; Luke Daly; Emmanuel Dartois; Elena Dobrică; Jean Duprat; Cecile Engrand; Dennis Harries; Minako Hashiguchi; Hope Ishii; Yoko Kebukawa; A. David Kilcoyne; Falko Langenhorst; Martin R. Lee; Larry R. Nittler; Eric Quirico; Taiga Okumura; Laurent Remusat; Scott Sandford; Hikaru Yabuta; Masanao Abe; Neyda M. Abreu; Paul A. J. Bagot; Pierre Beck; Laure Bejach; Phil A. Bland; John C. Bridges; Brittany A. Cymes; Alexandre Dazzi; Francisco de la Peña; Ariane Deniset‐Besseau; Satomi Enju; Yuma Enokido; David R. Frank; Jennifer Gray; Mitsutaka Haruta; Satoshi Hata; Leon Hicks; Yohei Igami; Damien Jacob; Kanami Kamide; Mutsumi Komatsu; Sylvain Laforet; Hugues Leroux; Corentin Le Guillou; Zita Martins; Maya Marinova; James Martinez; Jérémie Mathurin; Megumi Matsumoto; Toru Matsumoto; Junya Matsuno; Samuel McFadzean; Tatsuhiro Michikami; Itaru Mitsukawa; Akira Miyake; Masaaki Miyahara; Akiko Miyazaki; Gilles Montagnac; Smail Mostefaoui; Tomoki Nakamura; Aiko Nakato; Hiroshi Naraoka; Yusuke Nakauchi; Satoru Nakazawa; Masahiro Nishimura; Takaaki Noguchi; Kenta Ohtaki; Takuji Ohigashi; Tatsuaki Okada; Shota Okumura; Ryuji Okazaki; Thi H. V. Phan; Rolando Rebois; Kanako Sakamoto; Takanao Saiki; Hikaru Saito; Yusuke Seto; Miho Shigenaka; William Smith; Hiroki Suga; Mingqi Sun; Shogo Tachibana; Yoshio Takahashi; Yasuo Takeichi; Akihisa Takeuchi; Aki Takigawa; Yusuke Tamenori; Satoshi Tanaka; Fuyuto Terui; Michelle S. Thompson; Naotaka Tomioka; Akira Tsuchiyama; Yuichi Tsuda; Kentaro Uesugi; Masayuki Uesugi; Tomohiro Usui; Maximilien Verdier‐Paoletti; Daisuke Wakabayashi; Sei‐ichiro Watanabe; Toru Yada; Shohei Yamashita; Masahiro Yasutake; Kasumi Yogata; Makoto Yoshikawa; Hisayoshi Yurimoto; Pierre‐M. Zanetta; Thomas Zega; Michael E. Zolensky
    Meteoritics & Planetary Science Wiley 1086-9379 2024/01 [Refereed]
     
    Abstract Transmission electron microscopy analyses of Hayabusa2 samples show that Ryugu organic matter exhibits a range of morphologies, elemental compositions, and carbon functional chemistries consistent with those of carbonaceous chondrites that have experienced low‐temperature aqueous alteration. Both nanoglobules and diffuse organic matter are abundant. Non‐globular organic particles are also present, and including some that contain nanodiamond clusters. Diffuse organic matter is finely distributed in and around phyllosilicates, forms coatings on other minerals, and is also preserved in vesicles in secondary minerals such as carbonate and pyrrhotite. The average elemental compositions determined by energy‐dispersive spectroscopy of extracted, demineralized insoluble organic matter samples A0107 and C0106 are C100N3O9S1 and C100N3O7S1, respectively, with the difference in O/C slightly outside the difference in the standard error of the mean. The functional chemistry of the nanoglobules varies from mostly aromatic C=C to mixtures of aromatic C=C, ketone C=O, aliphatic (CHn), and carboxyl (COOH) groups. Diffuse organic matter associated with phyllosilicates has variable aromatic C, ketone and carboxyl groups, and some localized aliphatics, but is dominated by molecular carbonate (CO3) absorption, comparable to prior observations of clay‐bound organic matter in CI meteorites.
  • Van T. H. Phan; Pierre Beck; Rolando Rebois; Eric Quirico; Takaaki Noguchi; Toru Matsumoto; Akira Miyake; Yohei Igami; Mitsutaka Haruta; Hikaru Saito; Satoshi Hata; Yusuke Seto; Masaaki Miyahara; Naotaka Tomioka; Hope A. Ishii; John P. Bradley; Kenta K. Ohtaki; Elena Dobrică; Hugues Leroux; Corentin Le Guillou; Damien Jacob; Francisco de la Peña; Sylvain Laforet; Maya Marinova; Falko Langenhorst; Dennis Harries; Neyda M. Abreu; Jennifer Gray; Thomas Zega; Pierre‐M. Zanetta; Michelle S. Thompson; Rhonda Stroud; Jérémie Mathurin; Alexandre Dazzi; Emmanuel Dartois; Cécile Engrand; Kate Burgess; Brittany A. Cymes; John C. Bridges; Leon Hicks; Martin R. Lee; Luke Daly; Phil A. Bland; Michael E. Zolensky; David R. Frank; James Martinez; Akira Tsuchiyama; Masahiro Yasutake; Junya Matsuno; Shota Okumura; Itaru Mitsukawa; Kentaro Uesugi; Masayuki Uesugi; Akihisa Takeuchi; Mingqi Sun; Satomi Enju; Aki Takigawa; Tatsuhiro Michikami; Tomoki Nakamura; Megumi Matsumoto; Yusuke Nakauchi; Masanao Abe; Satoru Nakazawa; Tatsuaki Okada; Takanao Saiki; Satoshi Tanaka; Fuyuto Terui; Makoto Yoshikawa; Akiko Miyazaki; Aiko Nakato; Masahiro Nishimura; Tomohiro Usui; Toru Yada; Hisayoshi Yurimoto; Kazuhide Nagashima; Noriyuki Kawasaki; Naoya Sakamotoa; Peter Hoppe; Ryuji Okazaki; Hikaru Yabuta; Hiroshi Naraoka; Kanako Sakamoto; Shogo Tachibana; Sei‐ichiro Watanabe; Yuichi Tsuda
    Meteoritics & Planetary Science Wiley 1086-9379 2024/01 [Refereed]
     
    Abstract The Hayabusa2 mission from the Japan Aerospace Exploration Agency (JAXA) returned to the Earth samples of carbonaceous asteroid (162173) Ryugu. This mission offers a unique opportunity to investigate in the laboratory samples from a C‐type asteroid, without physical or chemical alteration by the terrestrial atmosphere. Here, we report on an investigation of the mineralogy and the organo‐chemistry of Hayabusa2 samples using a combination of micro‐ and nano‐infrared spectroscopy. Particles investigated with conventional FTIR spectroscopy have spectra dominated by phyllosilicate‐related absorption, as observed for samples of CI‐chondrites, selected ungrouped carbonaceous chondrites, and selected hydrated micrometeorites. Ryugu samples show smaller sulfate‐related absorption than CI‐chondrites. Our samples that were only briefly exposed to the Earth atmosphere show absorptions related to molecular water, revealing fast terrestrial contamination of the spectral signature at 3 μm. Overall, our FTIR data are in agreement with other work done on Ryugu samples, revealing a low degree of mineralogical variability across Ryugu samples. AFM‐IR mapping of the grains shows the presence of a micrometer‐sized organic globule in one of our analyzed grains. The AFM‐IR spectra obtained on this globule are similar to IR spectra obtained on IOM suggesting that it is constituted of refractory organic matter. This globule may host silicate in its interior, with a different mineralogy than bulk Ryugu phyllosilicate. The shape, presence of peculiar silicate, and the nature of organic constituting the globule point toward a pre‐accretionary origin of this globule and that at least part of Ryugu organics were inherited from the protosolar nebulae or the interstellar media. Altogether, our results show the similarities between Ryugu samples and CI chondrites.
  • Bahae‐eddine Mouloud; Damien Jacob; Francisco de la Peña; Maya Marinova; Corentin Le Guillou; Jean‐Christophe Viennet; Sylvain Laforet; Hugues Leroux; Adrien Teurtrie; Takaaki Noguchi; Toru Matsumoto; Akira Miyake; Yohei Igami; Mitsutaka Haruta; Hikaru Saito; Satoshi Hata; Yusuke Seto; Masaaki Miyahara; Naotaka Tomioka; Hope A. Ishii; John P. Bradley; Kenta K. Ohtaki; Elena Dobrica; Falko Langenhorst; Dennis Harries; Pierre Beck; Thi H. V. Phan; Rolando Rebois; Neyda M. Abreu; Jennifer Gray; Thomas Zega; Pierre‐M. Zanetta; Michelle S. Thompson; Rhonda Stroud; Kate Burgess; Brittany A. Cymes; John C. Bridges; Leon Hicks; Martin R. Lee; Luke Daly; Phil A. Bland; Michael E. Zolensky; David R. Frank; James Martinez; Akira Tsuchiyama; Masahiro Yasutake; Junya Matsuno; Shota Okumura; Itaru Mitsukawa; Kentaro Uesugi; Masayuki Uesugi; Akihisa Takeuchi; Mingqi Sun; Satomi Enju; Aki Takigawa; Tatsuhiro Michikami; Tomoki Nakamura; Megumi Matsumoto; Yusuke Nakauchi; Masanao Abe; Satoru Nakazawa; Tatsuaki Okada; Takanao Saiki; Satoshi Tanaka; Fuyuto Terui; Makoto Yoshikawa; Akiko Miyazaki; Aiko Nakato; Masahiro Nishimura; Tomohiro Usui; Toru Yada; Hisayoshi Yurimoto; Kazuhide Nagashima; Noriyuki Kawasaki; Naoya Sakamotoa; Ryuji Okazaki; Hikaru Yabuta; Hiroshi Naraoka; Kanako Sakamoto; Shogo Tachibana; Sei‐ichiro Watanabe; Yuichi Tsuda
    Meteoritics & Planetary Science Wiley 1086-9379 2024/01 [Refereed]
     
    Abstract Ryugu asteroid grains brought back to the Earth by the Hayabusa2 space mission are pristine samples containing hydrated minerals and organic compounds. Here, we investigate the mineralogy of their phyllosilicate‐rich matrix with four‐dimensional scanning transmission electron microscopy (4D‐STEM). We have identified and mapped the mineral phases at the nanometer scale (serpentine, smectite, pyrrhotite), observed the presence of Ni‐bearing pyrrhotite, and identified the serpentine polymorph as lizardite, in agreement with the reported aqueous alteration history of Ryugu. Furthermore, we have mapped the d‐spacings of smectite and observed a broad distribution of values, ranging from 1 to 2 nm, with an average d‐spacing of 1.24 nm, indicating significant heterogeneity within the sample. Such d‐spacing variability could be the result of either the presence of organic matter trapped in the interlayers or the influence of various geochemical conditions at the submicrometer scale, suggestive of a range of organic compounds and/or changes in smectite crystal chemistry.
  • Toru Matsumoto; Takaaki Noguchi; Akira Miyake; Yohei Igami; Mitsutaka Haruta; Yusuke Seto; Masaaki Miyahara; Naotaka Tomioka; Hikaru Saito; Satoshi Hata; Dennis Harries; Aki Takigawa; Yusuke Nakauchi; Shogo Tachibana; Tomoki Nakamura; Megumi Matsumoto; Hope A. Ishii; John P. Bradley; Kenta Ohtaki; Elena Dobrică; Hugues Leroux; Corentin Le Guillou; Damien Jacob; Francisco de la Peña; Sylvain Laforet; Maya Marinova; Falko Langenhorst; Pierre Beck; Thi H. V. Phan; Rolando Rebois; Neyda M. Abreu; Jennifer Gray; Thomas Zega; Pierre-M. Zanetta; Michelle S. Thompson; Rhonda Stroud; Kate Burgess; Brittany A. Cymes; John C. Bridges; Leon Hicks; Martin R. Lee; Luke Daly; Phil A. Bland; Michael E. Zolensky; David R. Frank; James Martinez; Akira Tsuchiyama; Masahiro Yasutake; Junya Matsuno; Shota Okumura; Itaru Mitsukawa; Kentaro Uesugi; Masayuki Uesugi; Akihisa Takeuchi; Mingqi Sun; Satomi Enju; Tatsuhiro Michikami; Hisayoshi Yurimoto; Ryuji Okazaki; Hikaru Yabuta; Hiroshi Naraoka; Kanako Sakamoto; Toru Yada; Masahiro Nishimura; Aiko Nakato; Akiko Miyazaki; Kasumi Yogata; Masanao Abe; Tatsuaki Okada; Tomohiro Usui; Makoto Yoshikawa; Takanao Saiki; Satoshi Tanaka; Fuyuto Terui; Satoru Nakazawa; Sei-ichiro Watanabe; Yuichi Tsuda
    Nature Astronomy Springer Science and Business Media LLC 8 (2) 207 - 215 2023/11 [Refereed]
     
    Abstract Large amounts of nitrogen compounds, such as ammonium salts, may be stored in icy bodies and comets, but the transport of these nitrogen-bearing solids into the near-Earth region is not well understood. Here, we report the discovery of iron nitride on magnetite grains from the surface of the near-Earth C-type carbonaceous asteroid Ryugu, suggesting inorganic nitrogen fixation. Micrometeoroid impacts and solar wind irradiation may have caused the selective loss of volatile species from major iron-bearing minerals to form the metallic iron. Iron nitride is a product of nitridation of the iron metal by impacts of micrometeoroids that have higher nitrogen contents than the CI chondrites. The impactors are probably primitive materials with origins in the nitrogen-rich reservoirs in the outer Solar System. Our observation implies that the amount of nitrogen available for planetary formation and prebiotic reactions in the inner Solar System is greater than previously recognized.
  • Takaaki Noguchi; Toru Matsumoto; Akira Miyake; Yohei Igami; Mitsutaka Haruta; Hikaru Saito; Satoshi Hata; Yusuke Seto; Masaaki Miyahara; Naotaka Tomioka; Hope A. Ishii; John P. Bradley; Kenta K. Ohtaki; Elena Dobrică; Hugues Leroux; Corentin Le Guillou; Damien Jacob; Francisco de la Peña; Sylvain Laforet; Bahae‐Eddine Mouloud; Maya Marinova; Falko Langenhorst; Dennis Harries; Pierre Beck; Thi H. V. Phan; Rolando Rebois; Neyda M. Abreu; Jennifer Gray; Thomas Zega; Pierre‐M. Zanetta; Michelle S. Thompson; Rhonda Stroud; Kate Burgess; Brittany A. Cymes; John C. Bridges; Leon Hicks; Martin R. Lee; Luke Daly; Phil A. Bland; William A. Smith; Sam McFadzean; Pierre‐Etienne Martin; Paul A. J. Bagot; Dennis Fougerouse; David W. Saxey; Steven Reddy; William D. A. Rickard; Michael E. Zolensky; David R. Frank; James Martinez; Akira Tsuchiyama; Masahiro Yasutake; Junya Matsuno; Shota Okumura; Itaru Mitsukawa; Kentaro Uesugi; Masayuki Uesugi; Akihisa Takeuchi; Mingqi Sun; Satomi Enju; Aki Takigawa; Tatsuhiro Michikami; Tomoki Nakamura; Megumi Matsumoto; Yusuke Nakauchi; Masanao Abe; Satoru Nakazawa; Tatsuaki Okada; Takanao Saiki; Satoshi Tanaka; Fuyuto Terui; Makoto Yoshikawa; Akiko Miyazaki; Aiko Nakato; Masahiro Nishimura; Tomohiro Usui; Toru Yada; Hisayoshi Yurimoto; Kazuhide Nagashima; Noriyuki Kawasaki; Naoya Sakamotoa; Peter Hoppe; Ryuji Okazaki; Hikaru Yabuta; Hiroshi Naraoka; Kanako Sakamoto; Shogo Tachibana; Sei‐ichiro Watanabe; Yuichi Tsuda
    Meteoritics & Planetary Science Wiley 1086-9379 2023/11 [Refereed]
     
    Abstract Samples returned from the carbonaceous asteroid (162173) Ryugu by the Hayabusa2 mission revealed that Ryugu is composed of materials consistent with CI chondrites and some types of space weathering. We report detailed mineralogy of the fine‐grained Ryugu samples allocated to our “Sand” team and report additional space weathering features found on the grains. The dominant mineralogy is composed of a fine‐grained mixture of Mg‐rich saponite and serpentine, magnetite, pyrrhotite, pentlandite, dolomite, and Fe‐bearing magnesite. These grains have mineralogy comparable to that of CI chondrites, showing severe aqueous alteration but lacking ferrihydrite and sulfate. These results are similar to previous works on large Ryugu grains. In addition to the major minerals, we also find many minerals that are rare or have not been reported among CI chondrites. Accessory minerals identified are hydroxyapatite, Mg‐Na phosphate, olivine, low‐Ca pyroxene, Mg‐Al spinel, chromite, manganochromite, eskolaite, ilmenite, cubanite, polydymite, transjordanite, schreibersite, calcite, moissanite, and poorly crystalline phyllosilicate. We also show scanning transmission electron microscope and scanning electron microscope compositional maps and images of some space‐weathered grains and severely heated and melted grains. Although our mineralogical results are consistent with that of millimeter‐sized grains, the fine‐grained fraction is best suited to investigate impact‐induced space weathering.
  • Akiko Miyazaki; Toru Yada; Kasumi Yogata; Kentaro Hatakeda; Aiko Nakato; Masahiro Nishimura; Kana Nagashima; Kazuya Kumagai; Yuya Hitomi; Hiromichi Soejima; Rui Tahara; Rei Kanemaru; Arisa Nakano; Miwa Yoshitake; Ayako Iwamae; Shizuho Furuya; Akira Tsuchiyama; Shogo Tachibana; Tatsuhiro Michikami; Tatsuaki Okada; Masanao Abe; Tomohiro Usui
    Earth, Planets and Space Springer Science and Business Media LLC 75 (1) 2023/11 [Refereed]
     
    Abstract The bulk density of grains from a celestial body is a fundamental property related to its composition and structure, contributing to the understanding of its evolutionary history. In this study, we provide the bulk density of 637 grains returned from the C-type near-Earth asteroid 162173 Ryugu. This is the largest number of grains to date for the curation activity, corresponding to 38 wt.% of the total returned samples (approximately 5.4 g). Although several densities of the Ryugu grains were reported, the volume estimation of some samples showed uncertainties. Therefore, we applied a new volume estimation model calibrated by X-ray micro-computed tomography (XCT) to the Ryugu grains to more accurately estimate their bulk density. The obtained average bulk density of 637 Ryugu grains was 1.79 ± 0.31 g/cm3 (1σ variation) for weights of 0.5‒100 mg (sub-mm ‒to 10 mm) irrespective of their 3D shapes characterized by three axial length ratios, considered to be a representative of the returned samples. The bulk density distributions of the grains in Chambers A and C were statistically distinguishable, with mean values of 1.81 ± 0.30 and 1.76 ± 0.33 g/cm3 (1σ variations), respectively. Despite the small difference, bulk density may have differed by sampling site. The obtained average bulk density value of A + C samples was almost the same as that of 16 Ryugu grains estimated based on CT scanned data, and was consistent with the densities of CI chondrites (1.57–1.91 g/cm3). The axial ratios of the grains in Chambers A and C were similar and those of the 724 returned samples and the flying particles ejected during the sampling operations were also similar, suggesting that relatively small Ryugu materials (mm‒cm in size) are similar in shape. The minor difference between the Rygu grains and flying particles could be attributed to events such as scraping during sampling operations and transportation. Graphical Abstract
  • Hugues Leroux; Corentin Le Guillou; Maya Marinova; Sylvain Laforet; Jean‐Christophe Viennet; Bahae‐Eddine Mouloud; Adrien Teurtrie; Francisco de la Peña; Damien Jacob; Daniel Hallatt; Mario Pelaez Fernandez; David Troadec; Takaaki Noguchi; Toru Matsumoto; Akira Miyake; Yohei Igami; Mitsutaka Haruta; Hikaru Saito; Satoshi Hata; Yusuke Seto; Masaaki Miyahara; Naotaka Tomioka; Hope A. Ishii; John P. Bradley; Kenta K. Ohtaki; Elena Dobrică; Falko Langenhorst; Dennis Harries; Pierre Beck; Thi H. V. Phan; Rolando Rebois; Neyda M. Abreu; Jennifer Gray; Thomas Zega; Pierre‐M. Zanetta; Michelle S. Thompson; Rhonda Stroud; Kate Burgess; Brittany A. Cymes; John C. Bridges; Leon Hicks; Martin R. Lee; Luke Daly; Phil A. Bland; Michael E. Zolensky; David R. Frank; James Martinez; Akira Tsuchiyama; Masahiro Yasutake; Junya Matsuno; Shota Okumura; Itaru Mitsukawa; Kentaro Uesugi; Masayuki Uesugi; Akihisa Takeuchi; Mingqi Sun; Satomi Enju; Aki Takigawa; Tatsuhiro Michikami; Tomoki Nakamura; Megumi Matsumoto; Yusuke Nakauchi; Masanao Abe; Satoru Nakazawa; Tatsuaki Okada; Takanao Saiki; Satoshi Tanaka; Fuyuto Terui; Makoto Yoshikawa; Akiko Miyazaki; Aiko Nakato; Masahiro Nishimura; Tomohiro Usui; Toru Yada; Hisayoshi Yurimoto; Kazuhide Nagashima; Noriyuki Kawasaki; Naoya Sakamotoa; Ryuji Okazaki; Hikaru Yabuta; Hiroshi Naraoka; Kanako Sakamoto; Shogo Tachibana; Sei‐Ichiro Watanabe; Yuichi Tsuda
    Meteoritics & Planetary Science Wiley 1086-9379 2023/11 [Refereed]
     
    Abstract Samples were recently collected from the carbonaceous asteroid (162173) Ryugu, by the Japan Aerospace Exploration Agency (JAXA) Hayabusa2 mission. They resemble CI chondrites material, thus showing clear evidence of extensive aqueous alteration attested by the widespread presence of a mixture of serpentine and saponite. We present here a scanning transmission electron microscopy study of the Ryugu dominant lithology of the phyllosilicate matrix at the nanometer scale, which we compare with that of the Orgueil CI chondrite. In both objects, the phyllosilicates are of comparable nature and texture, consisting of a mixture of small‐sized crystallites of serpentine and saponite. At the micrometer scale or less, the texture is an alternation of fine and coarse domains. The fine‐grained regions are dominated by saponite. In Ryugu, they enclose numerous Fe,Ni nanosulfides, whereas in Orgueil, S‐ and Ni‐rich ferrihydrite is abundant. The coarse‐grained regions contain more serpentine and no or little Fe,Ni sulfides or ferrihydrite. Scanning transmission x‐ray microscopy at the Fe‐L3 edge also reveals that iron valency of phyllosilicates is higher and more homogeneous in Orgueil (~70% Fe3+) than in Ryugu (<50% Fe3+). We interpret the observed textures as being mostly a consequence of aqueous alteration, likely resulting from the replacement by phyllosilicates of submicrometric components, initially agglomerated by a primary accretion. The fine‐grained domains may result from the replacement of GEMS (GEMS—glass with embedded metal and sulfides) objects or from other types of nanometric assemblages of silicate and Fe‐based nanophases. On the other hand, the coarse‐grained regions may correspond to the replacement of anhydrous crystalline silicates of the olivine and pyroxene type. The major difference is the presence of Fe,Ni sulfides in Ryugu and of ferrihydrite and higher iron valency of phyllosilicates in Orgueil. This might be due to long‐term terrestrial weathering that would have destabilized the nanosulfides. We also explore an alternative scenario involving more oxidizing hydrothermal conditions on the Orgueil parent body.
  • Elena Dobrică; Hope A. Ishii; John P. Bradley; Kenta Ohtaki; Adrian J. Brearley; Takaaki Noguchi; Toru Matsumoto; Akira Miyake; Yohei Igami; Mitsutaka Haruta; Hikaru Saito; Satoshi Hata; Yusuke Seto; Masaaki Miyahara; Naotaka Tomioka; Hugues Leroux; Corentin Le Guillou; Damien Jacob; Francisco de la Peña; Sylvain Laforet; Maya Marinova; Falko Langenhorst; Dennis Harries; Pierre Beck; Thi H.V. Phan; Rolando Rebois; Neyda M. Abreu; Jennifer Gray; Thomas Zega; Pierre-M. Zanetta; Michelle S. Thompson; Rhonda Stroud; Kate Burgess; Brittany A. Cymes; John C. Bridges; Leon Hicks; Martin R. Lee; Luke Daly; Phil A. Bland; Michael E. Zolensky; David R. Frank; James Martinez; Akira Tsuchiyama; Masahiro Yasutake; Junya Matsuno; Shota Okumura; Itaru Mitsukawa; Kentaro Uesugi; Masayuki Uesugi; Akihisa Takeuchi; Mingqi Sun; Satomi Enju; Aki Takigawa; Tatsuhiro Michikami; Tomoki Nakamura; Megumi Matsumoto; Yusuke Nakauchi; Hisayoshi Yurimoto; Ryuji Okazaki; Hikaru Yabuta; Hiroshi Naraoka; Kanako Sakamoto; Shogo Tachibana; Toru Yada; Masahiro Nishimura; Aiko Nakato; Akiko Miyazaki; Kasumi Yogata; Masanao Abe; Tatsuaki Okada; Tomohiro Usui; Makoto Yoshikawa; Takanao Saiki; Satoshi Tanaka; Fuyuto Terui; Satoru Nakazawa; Sei-ichiro Watanabe; Yuichi Tsuda
    Geochimica et Cosmochimica Acta Elsevier BV 346 65 - 75 0016-7037 2023/04 [Refereed]
  • Tatsuhiro Michikami; Akira Tsuchiyama; Axel Hagermann; Akio Takeda; Katsuki Shishido; Yushi Otsuka; Osamu Sasaki; Michihiko Nakamura; Satoshi Okumura; Harumasa Kano; Sunao Hasegawa
    Icarus Elsevier BV 392 115371 - 115371 0019-1035 2023/03 [Refereed]
  • Hikaru Yabuta; George D. Cody; Cécile Engrand; Yoko Kebukawa; Bradley De Gregorio; Lydie Bonal; Laurent Remusat; Rhonda Stroud; Eric Quirico; Larry Nittler; Minako Hashiguchi; Mutsumi Komatsu; Taiga Okumura; Jérémie Mathurin; Emmanuel Dartois; Jean Duprat; Yoshio Takahashi; Yasuo Takeichi; David Kilcoyne; Shohei Yamashita; Alexandre Dazzi; Ariane Deniset-Besseau; Scott Sandford; Zita Martins; Yusuke Tamenori; Takuji Ohigashi; Hiroki Suga; Daisuke Wakabayashi; Maximilien Verdier-Paoletti; Smail Mostefaoui; Gilles Montagnac; Jens Barosch; Kanami Kamide; Miho Shigenaka; Laure Bejach; Megumi Matsumoto; Yuma Enokido; Takaaki Noguchi; Hisayoshi Yurimoto; Tomoki Nakamura; Ryuji Okazaki; Hiroshi Naraoka; Kanako Sakamoto; Harold C. Connolly; Dante S. Lauretta; Masanao Abe; Tatsuaki Okada; Toru Yada; Masahiro Nishimura; Kasumi Yogata; Aiko Nakato; Miwa Yoshitake; Ayako Iwamae; Shizuho Furuya; Kentaro Hatakeda; Akiko Miyazaki; Hiromichi Soejima; Yuya Hitomi; Kazuya Kumagai; Tomohiro Usui; Tasuku Hayashi; Daiki Yamamoto; Ryota Fukai; Seiji Sugita; Kohei Kitazato; Naru Hirata; Rie Honda; Tomokatsu Morota; Eri Tatsumi; Naoya Sakatani; Noriyuki Namiki; Koji Matsumoto; Rina Noguchi; Koji Wada; Hiroki Senshu; Kazunori Ogawa; Yasuhiro Yokota; Yoshiaki Ishihara; Yuri Shimaki; Manabu Yamada; Chikatoshi Honda; Tatsuhiro Michikami; Moe Matsuoka; Naoyuki Hirata; Masahiko Arakawa; Chisato Okamoto; Masateru Ishiguro; Ralf Jaumann; Jean-Pierre Bibring; Matthias Grott; Stefan Schröder; Katharina Otto; Cedric Pilorget; Nicole Schmitz; Jens Biele; Tra-Mi Ho; Aurélie Moussi-Soffys; Akira Miura; Hirotomo Noda; Tetsuya Yamada; Keisuke Yoshihara; Kosuke Kawahara; Hitoshi Ikeda; Yukio Yamamoto; Kei Shirai; Shota Kikuchi; Naoko Ogawa; Hiroshi Takeuchi; Go Ono; Yuya Mimasu; Kent Yoshikawa; Yuto Takei; Atsushi Fujii; Yu-ichi Iijima; Satoru Nakazawa; Satoshi Hosoda; Takahiro Iwata; Masahiko Hayakawa; Hirotaka Sawada; Hajime Yano; Ryudo Tsukizaki; Masanobu Ozaki; Fuyuto Terui; Satoshi Tanaka; Masaki Fujimoto; Makoto Yoshikawa; Takanao Saiki; Shogo Tachibana; Sei-ichiro Watanabe; Yuichi Tsuda
    Science American Association for the Advancement of Science (AAAS) 379 (6634) 0036-8075 2023/02 [Refereed]
     
    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.
  • Hiroshi Naraoka; Yoshinori Takano; Jason P. Dworkin; Yasuhiro Oba; Kenji Hamase; Aogu Furusho; Nanako O. Ogawa; Minako Hashiguchi; Kazuhiko Fukushima; Dan Aoki; Philippe Schmitt-Kopplin; José C. Aponte; Eric T. Parker; Daniel P. Glavin; Hannah L. McLain; Jamie E. Elsila; Heather V. Graham; John M. Eiler; Francois-Regis Orthous-Daunay; Cédric Wolters; Junko Isa; Véronique Vuitton; Roland Thissen; Saburo Sakai; Toshihiro Yoshimura; Toshiki Koga; Naohiko Ohkouchi; Yoshito Chikaraishi; Haruna Sugahara; Hajime Mita; Yoshihiro Furukawa; Norbert Hertkorn; Alexander Ruf; Hisayoshi Yurimoto; Tomoki Nakamura; Takaaki Noguchi; Ryuji Okazaki; Hikaru Yabuta; Kanako Sakamoto; Shogo Tachibana; Harold C. Connolly; Dante S. Lauretta; Masanao Abe; Toru Yada; Masahiro Nishimura; Kasumi Yogata; Aiko Nakato; Miwa Yoshitake; Ayako Suzuki; Akiko Miyazaki; Shizuho Furuya; Kentaro Hatakeda; Hiromichi Soejima; Yuya Hitomi; Kazuya Kumagai; Tomohiro Usui; Tasuku Hayashi; Daiki Yamamoto; Ryota Fukai; Kohei Kitazato; Seiji Sugita; Noriyuki Namiki; Masahiko Arakawa; Hitoshi Ikeda; Masateru Ishiguro; Naru Hirata; Koji Wada; Yoshiaki Ishihara; Rina Noguchi; Tomokatsu Morota; Naoya Sakatani; Koji Matsumoto; Hiroki Senshu; Rie Honda; Eri Tatsumi; Yasuhiro Yokota; Chikatoshi Honda; Tatsuhiro Michikami; Moe Matsuoka; Akira Miura; Hirotomo Noda; Tetsuya Yamada; Keisuke Yoshihara; Kosuke Kawahara; Masanobu Ozaki; Yu-ichi Iijima; Hajime Yano; Masahiko Hayakawa; Takahiro Iwata; Ryudo Tsukizaki; Hirotaka Sawada; Satoshi Hosoda; Kazunori Ogawa; Chisato Okamoto; Naoyuki Hirata; Kei Shirai; Yuri Shimaki; Manabu Yamada; Tatsuaki Okada; Yukio Yamamoto; Hiroshi Takeuchi; Atsushi Fujii; Yuto Takei; Kento Yoshikawa; Yuya Mimasu; Go Ono; Naoko Ogawa; Shota Kikuchi; Satoru Nakazawa; Fuyuto Terui; Satoshi Tanaka; Takanao Saiki; Makoto Yoshikawa; Sei-ichiro Watanabe; Yuichi Tsuda
    Science American Association for the Advancement of Science (AAAS) 379 (6634) 0036-8075 2023/02 [Refereed]
     
    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.
  • Takaaki Noguchi; Toru Matsumoto; Akira Miyake; Yohei Igami; Mitsutaka Haruta; Hikaru Saito; Satoshi Hata; Yusuke Seto; Masaaki Miyahara; Naotaka Tomioka; Hope A. Ishii; John P. Bradley; Kenta K. Ohtaki; Elena Dobrică; Hugues Leroux; Corentin Le Guillou; Damien Jacob; Francisco de la Peña; Sylvain Laforet; Maya Marinova; Falko Langenhorst; Dennis Harries; Pierre Beck; Thi H. V. Phan; Rolando Rebois; Neyda M. Abreu; Jennifer Gray; Thomas Zega; Pierre-M. Zanetta; Michelle S. Thompson; Rhonda Stroud; Kate Burgess; Brittany A. Cymes; John C. Bridges; Leon Hicks; Martin R. Lee; Luke Daly; Phil A. Bland; Michael E. Zolensky; David R. Frank; James Martinez; Akira Tsuchiyama; Masahiro Yasutake; Junya Matsuno; Shota Okumura; Itaru Mitsukawa; Kentaro Uesugi; Masayuki Uesugi; Akihisa Takeuchi; Mingqi Sun; Satomi Enju; Aki Takigawa; Tatsuhiro Michikami; Tomoki Nakamura; Megumi Matsumoto; Yusuke Nakauchi; Masanao Abe; Masahiko Arakawa; Atsushi Fujii; Masahiko Hayakawa; Naru Hirata; Naoyuki Hirata; Rie Honda; Chikatoshi Honda; Satoshi Hosoda; Yu-ichi Iijima; Hitoshi Ikeda; Masateru Ishiguro; Yoshiaki Ishihara; Takahiro Iwata; Kousuke Kawahara; Shota Kikuchi; Kohei Kitazato; Koji Matsumoto; Moe Matsuoka; Yuya Mimasu; Akira Miura; Tomokatsu Morota; Satoru Nakazawa; Noriyuki Namiki; Hirotomo Noda; Rina Noguchi; Naoko Ogawa; Kazunori Ogawa; Tatsuaki Okada; Chisato Okamoto; Go Ono; Masanobu Ozaki; Takanao Saiki; Naoya Sakatani; Hirotaka Sawada; Hiroki Senshu; Yuri Shimaki; Kei Shirai; Seiji Sugita; Yuto Takei; Hiroshi Takeuchi; Satoshi Tanaka; Eri Tatsumi; Fuyuto Terui; Ryudo Tsukizaki; Koji Wada; Manabu Yamada; Tetsuya Yamada; Yukio Yamamoto; Hajime Yano; Yasuhiro Yokota; Keisuke Yoshihara; Makoto Yoshikawa; Kent Yoshikawa; Ryohta Fukai; Shizuho Furuya; Kentaro Hatakeda; Tasuku Hayashi; Yuya Hitomi; Kazuya Kumagai; Akiko Miyazaki; Aiko Nakato; Masahiro Nishimura; Hiromichi Soejima; Ayako I. Suzuki; Tomohiro Usui; Toru Yada; Daiki Yamamoto; Kasumi Yogata; Miwa Yoshitake; Harold C. Connolly; Dante S. Lauretta; Hisayoshi Yurimoto; Kazuhide Nagashima; Noriyuki Kawasaki; Naoya Sakamoto; Ryuji Okazaki; Hikaru Yabuta; Hiroshi Naraoka; Kanako Sakamoto; Shogo Tachibana; Sei-ichiro Watanabe; Yuichi Tsuda
    Nature Astronomy Springer Science and Business Media LLC 2022/12 [Refereed]
     
    Abstract Without a protective atmosphere, space-exposed surfaces of airless Solar System bodies gradually experience an alteration in composition, structure and optical properties through a collective process called space weathering. The return of samples from near-Earth asteroid (162173) Ryugu by Hayabusa2 provides the first opportunity for laboratory study of space-weathering signatures on the most abundant type of inner solar system body: a C-type asteroid, composed of materials largely unchanged since the formation of the Solar System. Weathered Ryugu grains show areas of surface amorphization and partial melting of phyllosilicates, in which reduction from Fe3+ to Fe2+ and dehydration developed. Space weathering probably contributed to dehydration by dehydroxylation of Ryugu surface phyllosilicates that had already lost interlayer water molecules and to weakening of the 2.7 µm hydroxyl (–OH) band in reflectance spectra. For C-type asteroids in general, this indicates that a weak 2.7 µm band can signify space-weathering-induced surface dehydration, rather than bulk volatile loss.
  • Ryuji Okazaki; Yayoi N. Miura; Yoshinori Takano; Hirotaka Sawada; Kanako Sakamoto; Toru Yada; Keita Yamada; Shinsuke Kawagucci; Yohei Matsui; Ko Hashizume; Akizumi Ishida; Michael W. Broadley; Bernard Marty; David Byrne; Evelyn Füri; Alex Meshik; Olga Pravdivtseva; Henner Busemann; My E.I. Riebe; Jamie Gilmour; Jisun Park; Ken-ichi Bajo; Kevin Righter; Saburo Sakai; Shun Sekimoto; Fumio Kitajima; Sarah A. Crowther; Naoyoshi Iwata; Naoki Shirai; Mitsuru Ebihara; Reika Yokochi; Kunihiko Nishiizumi; Keisuke Nagao; Jong Ik Lee; Patricia Clay; Akihiro Kano; Marc W. Caffee; Ryu Uemura; Makoto Inagaki; Daniela Krietsch; Colin Maden; Mizuki Yamamoto; Lydia Fawcett; Thomas Lawton; Tomoki Nakamura; Hiroshi Naraoka; Takaaki Noguchi; Hikaru Yabuta; Hisayoshi Yurimoto; Yuichi Tsuda; Sei-ichiro Watanabe; Masanao Abe; Masahiko Arakawa; Atsushi Fujii; Masahiko Hayakawa; Naoyuki Hirata; Naru Hirata; Rie Honda; Chikatoshi Honda; Satoshi Hosoda; Yu-ichi Iijima; Hitoshi Ikeda; Masateru Ishiguro; Yoshiaki Ishihara; Takahiro Iwata; Kosuke Kawahara; Shota Kikuchi; Kohei Kitazato; Koji Matsumoto; Moe Matsuoka; Tatsuhiro Michikami; Yuya Mimasu; Akira Miura; Tomokatsu Morota; Satoru Nakazawa; Noriyuki Namiki; Hirotomo Noda; Rina Noguchi; Naoko Ogawa; Kazunori Ogawa; Tatsuaki Okada; Chisato Okamoto; Go Ono; Masanobu Ozaki; Takanao Saiki; Naoya Sakatani; Hiroki Senshu; Yuri Shimaki; Kei Shirai; Seiji Sugita; Yuto Takei; Hiroshi Takeuchi; Satoshi Tanaka; Eri Tatsumi; Fuyuto Terui; Ryudo Tsukizaki; Koji Wada; Manabu Yamada; Tetsuya Yamada; Yukio Yamamoto; Hajime Yano; Yasuhiro Yokota; Keisuke Yoshihara; Makoto Yoshikawa; Kent Yoshikawa; Shizuho Furuya; Kentaro Hatakeda; Tasuku Hayashi; Yuya Hitomi; Kazuya Kumagai; Akiko Miyazaki; Aiko Nakato; Masahiro Nishimura; Hiromichi Soejima; Ayako Iwamae; Daiki Yamamoto; Kasumi Yogata; Miwa Yoshitake; Ryota Fukai; Tomohiro Usui; Trevor Ireland; Harold C. Connolly; Dante S. Lauretta; Shogo Tachibana
    Science Advances American Association for the Advancement of Science (AAAS) 8 (46) 2022/11 [Refereed]
     
    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 3 He/ 4 He and 20 Ne/ 22 Ne 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.
  • Ryuji Okazaki; Bernard Marty; Henner Busemann; Ko Hashizume; Jamie D. Gilmour; Alex Meshik; Toru Yada; Fumio Kitajima; Michael W. Broadley; David Byrne; Evelyn Füri; My E. I. Riebe; Daniela Krietsch; Colin Maden; Akizumi Ishida; Patricia Clay; Sarah A. Crowther; Lydia Fawcett; Thomas Lawton; Olga Pravdivtseva; Yayoi N. Miura; Jisun Park; Ken-ichi Bajo; Yoshinori Takano; Keita Yamada; Shinsuke Kawagucci; Yohei Matsui; Mizuki Yamamoto; Kevin Righter; Saburo Sakai; Naoyoshi Iwata; Naoki Shirai; Shun Sekimoto; Makoto Inagaki; Mitsuru Ebihara; Reika Yokochi; Kunihiko Nishiizumi; Keisuke Nagao; Jong Ik Lee; Akihiro Kano; Marc W. Caffee; Ryu Uemura; Tomoki Nakamura; Hiroshi Naraoka; Takaaki Noguchi; Hikaru Yabuta; Hisayoshi Yurimoto; Shogo Tachibana; Hirotaka Sawada; Kanako Sakamoto; Masanao Abe; Masahiko Arakawa; Atsushi Fujii; Masahiko Hayakawa; Naoyuki Hirata; Naru Hirata; Rie Honda; Chikatoshi Honda; Satoshi Hosoda; Yu-ichi Iijima; Hitoshi Ikeda; Masateru Ishiguro; Yoshiaki Ishihara; Takahiro Iwata; Kosuke Kawahara; Shota Kikuchi; Kohei Kitazato; Koji Matsumoto; Moe Matsuoka; Tatsuhiro Michikami; Yuya Mimasu; Akira Miura; Tomokatsu Morota; Satoru Nakazawa; Noriyuki Namiki; Hirotomo Noda; Rina Noguchi; Naoko Ogawa; Kazunori Ogawa; Tatsuaki Okada; Chisato Okamoto; Go Ono; Masanobu Ozaki; Takanao Saiki; Naoya Sakatani; Hiroki Senshu; Yuri Shimaki; Kei Shirai; Seiji Sugita; Yuto Takei; Hiroshi Takeuchi; Satoshi Tanaka; Eri Tatsumi; Fuyuto Terui; Ryudo Tsukizaki; Koji Wada; Manabu Yamada; Tetsuya Yamada; Yukio Yamamoto; Hajime Yano; Yasuhiro Yokota; Keisuke Yoshihara; Makoto Yoshikawa; Kent Yoshikawa; Shizuho Furuya; Kentaro Hatakeda; Tasuku Hayashi; Yuya Hitomi; Kazuya Kumagai; Akiko Miyazaki; Aiko Nakato; Masahiro Nishimura; Hiromichi Soejima; Ayako Iwamae; Daiki Yamamoto; Kasumi Yogata; Miwa Yoshitake; Ryota Fukai; Tomohiro Usui; Harold C. Connolly; Dante Lauretta; Sei-ichiro Watanabe; Yuichi Tsuda
    Science American Association for the Advancement of Science (AAAS) 379 (6634) 0036-8075 2022/10 [Refereed]
     
    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 measure noble gas and nitrogen isotopes in Ryugu samples, finding they are dominated by pre-solar 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 heterogeneous abundances between the samples. Our measurements support a close relationship between Ryugu and CI chondrites. Noble gases produced by galactic cosmic rays, indicating ~5 Myr exposure, and from implanted solar wind, record the recent irradiation history of Ryugu after it migrated to its current orbit.
  • T. Nakamura; M. Matsumoto; K. Amano; Y. Enokido; M. E. Zolensky; T. Mikouchi; H. Genda; S. Tanaka; M. Y. Zolotov; K. Kurosawa; S. Wakita; R. Hyodo; H. Nagano; D. Nakashima; Y. Takahashi; Y. Fujioka; M. Kikuiri; E. Kagawa; M. Matsuoka; A. J. Brearley; A. Tsuchiyama; M. Uesugi; J. Matsuno; Y. Kimura; M. Sato; R. E. Milliken; E. Tatsumi; S. Sugita; T. Hiroi; K. Kitazato; D. Brownlee; D. J. Joswiak; M. Takahashi; K. Ninomiya; T. Takahashi; T. Osawa; K. Terada; F. E. Brenker; B. J. Tkalcec; L. Vincze; R. Brunetto; A. Aléon-Toppani; Q. H. S. Chan; M. Roskosz; J.-C. Viennet; P. Beck; E. E. Alp; T. Michikami; Y. Nagaashi; T. Tsuji; Y. Ino; J. Martinez; J. Han; A. Dolocan; R. J. Bodnar; M. Tanaka; H. Yoshida; K. Sugiyama; A. J. King; K. Fukushi; H. Suga; S. Yamashita; T. Kawai; K. Inoue; A. Nakato; T. Noguchi; F. Vilas; A. R. Hendrix; C. Jaramillo-Correa; D. L. Domingue; G. Dominguez; Z. Gainsforth; C. Engrand; J. Duprat; S. S. Russell; E. Bonato; C. Ma; T. Kawamoto; T. Wada; S. Watanabe; R. Endo; S. Enju; L. Riu; S. Rubino; P. Tack; S. Takeshita; Y. Takeichi; A. Takeuchi; A. Takigawa; D. Takir; T. Tanigaki; A. Taniguchi; K. Tsukamoto; T. Yagi; S. Yamada; K. Yamamoto; Y. Yamashita; M. Yasutake; K. Uesugi; I. Umegaki; I. Chiu; T. Ishizaki; S. Okumura; E. Palomba; C. Pilorget; S. M. Potin; A. Alasli; S. Anada; Y. Araki; N. Sakatani; C. Schultz; O. Sekizawa; S. D. Sitzman; K. Sugiura; M. Sun; E. Dartois; E. De Pauw; Z. Dionnet; Z. Djouadi; G. Falkenberg; R. Fujita; T. Fukuma; I. R. Gearba; K. Hagiya; M. Y. Hu; T. Kato; T. Kawamura; M. Kimura; M. K. Kubo; F. Langenhorst; C. Lantz; B. Lavina; M. Lindner; J. Zhao; B. Vekemans; D. Baklouti; B. Bazi; F. Borondics; S. Nagasawa; G. Nishiyama; K. Nitta; J. Mathurin; T. Matsumoto; I. Mitsukawa; H. Miura; A. Miyake; Y. Miyake; H. Yurimoto; R. Okazaki; H. Yabuta; H. Naraoka; K. Sakamoto; S. Tachibana; H. C. Connolly; D. S. Lauretta; M. Yoshitake; M. Yoshikawa; K. Yoshikawa; K. Yoshihara; Y. Yokota; K. Yogata; H. Yano; Y. Yamamoto; D. Yamamoto; M. Yamada; T. Yamada; T. Yada; K. Wada; T. Usui; R. Tsukizaki; F. Terui; H. Takeuchi; Y. Takei; A. Iwamae; H. Soejima; K. Shirai; Y. Shimaki; H. Senshu; H. Sawada; T. Saiki; M. Ozaki; G. Ono; T. Okada; N. Ogawa; K. Ogawa; R. Noguchi; H. Noda; M. Nishimura; N. Namiki; S. Nakazawa; T. Morota; A. Miyazaki; A. Miura; Y. Mimasu; K. Matsumoto; K. Kumagai; T. Kouyama; S. Kikuchi; K. Kawahara; S. Kameda; T. Iwata; Y. Ishihara; M. Ishiguro; H. Ikeda; S. Hosoda; R. Honda; C. Honda; Y. Hitomi; N. Hirata; N. Hirata; T. Hayashi; M. Hayakawa; K. Hatakeda; S. Furuya; R. Fukai; A. Fujii; Y. Cho; M. Arakawa; M. Abe; S. Watanabe; Y. Tsuda
    Science American Association for the Advancement of Science (AAAS) 379 (6634) 0036-8075 2022/09 [Refereed]
     
    Samples of the carbonaceous asteroid Ryugu were brought to Earth by the Hayabusa2 spacecraft. We analyzed seventeen Ryugu samples measuring 1-8 mm. CO 2 -bearing water inclusions are present within a pyrrhotite crystal, indicating that Ryugu’s parent asteroid formed in the outer Solar System. The samples contain low abundances of materials that formed at high temperatures, such as chondrules and Ca, Al-rich inclusions. The samples are rich in phyllosilicates and carbonates, which formed by aqueous alteration reactions at low temperature, high pH, and water/rock ratios < 1 (by mass). Less altered fragments contain olivine, pyroxene, amorphous silicates, calcite, and phosphide. Numerical simulations, based on the mineralogical and physical properties of the samples, indicate Ryugu’s parent body formed ~ 2 million years after the beginning of Solar System formation.
  • Motoo Ito; Naotaka Tomioka; Masayuki Uesugi; Akira Yamaguchi; Naoki Shirai; Takuji Ohigashi; Ming-Chang Liu; Richard C. Greenwood; Makoto Kimura; Naoya Imae; Kentaro Uesugi; Aiko Nakato; Kasumi Yogata; Hayato Yuzawa; Yu Kodama; Akira Tsuchiyama; Masahiro Yasutake; Ross Findlay; Ian A. Franchi; James A. Malley; Kaitlyn A. McCain; Nozomi Matsuda; Kevin D. McKeegan; Kaori Hirahara; Akihisa Takeuchi; Shun Sekimoto; Ikuya Sakurai; Ikuo Okada; Yuzuru Karouji; Masahiko Arakawa; Atsushi Fujii; Masaki Fujimoto; Masahiko Hayakawa; Naoyuki Hirata; Naru Hirata; Rie Honda; Chikatoshi Honda; Satoshi Hosoda; Yu-ichi Iijima; Hitoshi Ikeda; Masateru Ishiguro; Yoshiaki Ishihara; Takahiro Iwata; Kosuke Kawahara; Shota Kikuchi; Kohei Kitazato; Koji Matsumoto; Moe Matsuoka; Tatsuhiro Michikami; Yuya Mimasu; Akira Miura; Osamu Mori; Tomokatsu Morota; Satoru Nakazawa; Noriyuki Namiki; Hirotomo Noda; Rina Noguchi; Naoko Ogawa; Kazunori Ogawa; Tatsuaki Okada; Chisato Okamoto; Go Ono; Masanobu Ozaki; Takanao Saiki; Naoya Sakatani; Hirotaka Sawada; Hiroki Senshu; Yuri Shimaki; Kei Shirai; Seiji Sugita; Yuto Takei; Hiroshi Takeuchi; Satoshi Tanaka; Eri Tatsumi; Fuyuto Terui; Ryudo Tsukizaki; Koji Wada; Manabu Yamada; Tetsuya Yamada; Yukio Yamamoto; Hajime Yano; Yasuhiro Yokota; Keisuke Yoshihara; Makoto Yoshikawa; Kent Yoshikawa; Ryota Fukai; Shizuho Furuya; Kentaro Hatakeda; Tasuku Hayashi; Yuya Hitomi; Kazuya Kumagai; Akiko Miyazaki; Masahiro Nishimura; Hiromichi Soejima; Ayako Iwamae; Daiki Yamamoto; Miwa Yoshitake; Toru Yada; Masanao Abe; Tomohiro Usui; Sei-ichiro Watanabe; Yuichi Tsuda
    Nature Astronomy Springer Science and Business Media LLC 6 (10) 1163 - 1171 2022/08 [Refereed]
     
    Abstract Volatile and organic-rich C-type asteroids may have been one of the main sources of Earth’s water. Our best insight into their chemistry is currently provided by carbonaceous chondritic meteorites, but the meteorite record is biased: only the strongest types survive atmospheric entry and are then modified by interaction with the terrestrial environment. Here we present the results of a detailed bulk and microanalytical study of pristine Ryugu particles, brought to Earth by the Hayabusa2 spacecraft. Ryugu particles display a close compositional match with the chemically unfractionated, but aqueously altered, CI (Ivuna-type) chondrites, which are widely used as a proxy for the bulk Solar System composition. The sample shows an intricate spatial relationship between aliphatic-rich organics and phyllosilicates and indicates maximum temperatures of ~30 °C during aqueous alteration. We find that heavy hydrogen and nitrogen abundances are consistent with an outer Solar System origin. Ryugu particles are the most uncontaminated and unfractionated extraterrestrial materials studied so far, and provide the best available match to the bulk Solar System composition.
  • Eizo NAKAMURA; Katsura KOBAYASHI; Ryoji TANAKA; Tak KUNIHIRO; Hiroshi KITAGAWA; Christian POTISZIL; Tsutomu OTA; Chie SAKAGUCHI; Masahiro YAMANAKA; Dilan M. RATNAYAKE; Havishk TRIPATHI; Rahul KUMAR; Maya-Liliana AVRAMESCU; Hidehisa TSUCHIDA; Yusuke YACHI; Hitoshi MIURA; Masanao ABE; Ryota FUKAI; Shizuho FURUYA; Kentaro HATAKEDA; Tasuku HAYASHI; Yuya HITOMI; Kazuya KUMAGAI; Akiko MIYAZAKI; Aiko NAKATO; Masahiro NISHIMURA; Tatsuaki OKADA; Hiromichi SOEJIMA; Seiji SUGITA; Ayako SUZUKI; Tomohiro USUI; Toru YADA; Daiki YAMAMOTO; Kasumi YOGATA; Miwa YOSHITAKE; Masahiko ARAKAWA; Atsushi FUJII; Masahiko HAYAKAWA; Naoyuki HIRATA; Naru HIRATA; Rie HONDA; Chikatoshi HONDA; Satoshi HOSODA; Yu-ichi IIJIMA; Hitoshi IKEDA; Masateru ISHIGURO; Yoshiaki ISHIHARA; Takahiro IWATA; Kosuke KAWAHARA; Shota KIKUCHI; Kohei KITAZATO; Koji MATSUMOTO; Moe MATSUOKA; Tatsuhiro MICHIKAMI; Yuya MIMASU; Akira MIURA; Tomokatsu MOROTA; Satoru NAKAZAWA; Noriyuki NAMIKI; Hirotomo NODA; Rina NOGUCHI; Naoko OGAWA; Kazunori OGAWA; Chisato OKAMOTO; Go ONO; Masanobu OZAKI; Takanao SAIKI; Naoya SAKATANI; Hirotaka SAWADA; Hiroki SENSHU; Yuri SHIMAKI; Kei SHIRAI; Yuto TAKEI; Hiroshi TAKEUCHI; Satoshi TANAKA; Eri TATSUMI; Fuyuto TERUI; Ryudo TSUKIZAKI; Koji WADA; Manabu YAMADA; Tetsuya YAMADA; Yukio YAMAMOTO; Hajime YANO; Yasuhiro YOKOTA; Keisuke YOSHIHARA; Makoto YOSHIKAWA; Kent YOSHIKAWA; Masaki FUJIMOTO; Sei-ichiro WATANABE; Yuichi TSUDA
    Proceedings of the Japan Academy, Series B Japan Academy 98 (6) 227 - 282 0386-2208 2022/06 [Refereed]
  • Tetsuya Yokoyama; Kazuhide Nagashima; Izumi Nakai; Edward D. Young; Yoshinari Abe; Jérôme Aléon; Conel M. O’D. Alexander; Sachiko Amari; Yuri Amelin; Ken-ichi Bajo; Martin Bizzarro; Audrey Bouvier; Richard W. Carlson; Marc Chaussidon; Byeon-Gak Choi; Nicolas Dauphas; Andrew M. Davis; Tommaso Di Rocco; Wataru Fujiya; Ryota Fukai; Ikshu Gautam; Makiko K. Haba; Yuki Hibiya; Hiroshi Hidaka; Hisashi Homma; Peter Hoppe; Gary R. Huss; Kiyohiro Ichida; Tsuyoshi Iizuka; Trevor R. Ireland; Akira Ishikawa; Motoo Ito; Shoichi Itoh; Noriyuki Kawasaki; Noriko T. Kita; Kouki Kitajima; Thorsten Kleine; Shintaro Komatani; Alexander N. Krot; Ming-Chang Liu; Yuki Masuda; Kevin D. McKeegan; Mayu Morita; Kazuko Motomura; Frédéric Moynier; Ann Nguyen; Larry Nittler; Morihiko Onose; Andreas Pack; Changkun Park; Laurette Piani; Liping Qin; Sara S. Russell; Naoya Sakamoto; Maria Schönbächler; Lauren Tafla; Haolan Tang; Kentaro Terada; Yasuko Terada; Tomohiro Usui; Sohei Wada; Meenakshi Wadhwa; Richard J. Walker; Katsuyuki Yamashita; Qing-Zhu Yin; Shigekazu Yoneda; Hiroharu Yui; Ai-Cheng Zhang; Harold C. Connolly; Dante S. Lauretta; Tomoki Nakamura; Hiroshi Naraoka; Takaaki Noguchi; Ryuji Okazaki; Kanako Sakamoto; Hikaru Yabuta; Masanao Abe; Masahiko Arakawa; Atsushi Fujii; Masahiko Hayakawa; Naoyuki Hirata; Naru Hirata; Rie Honda; Chikatoshi Honda; Satoshi Hosoda; Yu-ichi Iijima; Hitoshi Ikeda; Masateru Ishiguro; Yoshiaki Ishihara; Takahiro Iwata; Kosuke Kawahara; Shota Kikuchi; Kohei Kitazato; Koji Matsumoto; Moe Matsuoka; Tatsuhiro Michikami; Yuya Mimasu; Akira Miura; Tomokatsu Morota; Satoru Nakazawa; Noriyuki Namiki; Hirotomo Noda; Rina Noguchi; Naoko Ogawa; Kazunori Ogawa; Tatsuaki Okada; Chisato Okamoto; Go Ono; Masanobu Ozaki; Takanao Saiki; Naoya Sakatani; Hirotaka Sawada; Hiroki Senshu; Yuri Shimaki; Kei Shirai; Seiji Sugita; Yuto Takei; Hiroshi Takeuchi; Satoshi Tanaka; Eri Tatsumi; Fuyuto Terui; Yuichi Tsuda; Ryudo Tsukizaki; Koji Wada; Sei-ichiro Watanabe; Manabu Yamada; Tetsuya Yamada; Yukio Yamamoto; Hajime Yano; Yasuhiro Yokota; Keisuke Yoshihara; Makoto Yoshikawa; Kent Yoshikawa; Shizuho Furuya; Kentaro Hatakeda; Tasuku Hayashi; Yuya Hitomi; Kazuya Kumagai; Akiko Miyazaki; Aiko Nakato; Masahiro Nishimura; Hiromichi Soejima; Ayako Suzuki; Toru Yada; Daiki Yamamoto; Kasumi Yogata; Miwa Yoshitake; Shogo Tachibana; Hisayoshi Yurimoto
    Science American Association for the Advancement of Science (AAAS) 379 (6634) 0036-8075 2022/06 [Refereed]
     
    Carbonaceous meteorites are thought to be fragments of C-type (carbonaceous) asteroids. Samples of the C-type asteroid (162173) Ryugu were retrieved by the Hayabusa2 spacecraft. We measure the mineralogy, bulk chemical and isotopic compositions of Ryugu samples. They are mainly composed of materials similar to carbonaceous chondrite meteorites, particularly the CI (Ivuna-type) group. The samples consist predominantly of minerals formed in aqueous fluid on a parent planetesimal. The primary minerals were altered by fluids at a temperature of 37 ± 10°C, (Stat.) (Syst.) million years after formation of the first solids in the Solar System. After aqueous alteration, the Ryugu samples were likely never heated above ~100°C. The samples have a chemical composition that more closely resembles the Sun’s photosphere than other natural samples do.
  • Shota Kikuchi; Sei-ichiro Watanabe; Koji Wada; Takanao Saiki; Hikaru Yabuta; Seiji Sugita; Masanao Abe; Masahiko Arakawa; Yuichiro Cho; Masahiko Hayakawa; Naoyuki Hirata; Naru Hirata; Chikatoshi Honda; Rie Honda; Ko Ishibashi; Yoshiaki Ishihara; Takahiro Iwata; Toshihiko Kadono; Shingo Kameda; Kohei Kitazato; Toru Kouyama; Koji Matsumoto; Moe Matsuoka; Tatsuhiro Michikami; Yuya Mimasu; Akira Miura; Tomokatsu Morota; Tomoki Nakamura; Satoru Nakazawa; Noriyuki Namiki; Rina Noguchi; Kazunori Ogawa; Naoko Ogawa; Tatsuaki Okada; Go Ono; Naoya Sakatani; Hirotaka Sawada; Hiroki Senshu; Yuri Shimaki; Kei Shirai; Shogo Tachibana; Yuto Takei; Satoshi Tanaka; Eri Tatsumi; Fuyuto Terui; Manabu Yamada; Yukio Yamamoto; Yasuhiro Yokota; Kent Yoshikawa; Makoto Yoshikawa; Yuichi Tsuda
    Planetary and Space Science Elsevier BV 219 105519 - 105519 0032-0633 2022/06 [Refereed]
  • S. Tachibana; H. Sawada; R. Okazaki; Y. Takano; K. Sakamoto; Y. N. Miura; C. Okamoto; H. Yano; S. Yamanouchi; P. Michel; Y. Zhang; S. Schwartz; F. Thuillet; H. Yurimoto; T. Nakamura; T. Noguchi; H. Yabuta; H. Naraoka; A. Tsuchiyama; N. Imae; K. Kurosawa; A. M. Nakamura; K. Ogawa; S. Sugita; T. Morota; R. Honda; S. Kameda; E. Tatsumi; Y. Cho; K. Yoshioka; Y. Yokota; M. Hayakawa; M. Matsuoka; N. Sakatani; M. Yamada; T. Kouyama; H. Suzuki; C. Honda; T. Yoshimitsu; T. Kubota; H. Demura; T. Yada; M. Nishimura; K. Yogata; A. Nakato; M. Yoshitake; A. I. Suzuki; S. Furuya; K. Hatakeda; A. Miyazaki; K. Kumagai; T. Okada; M. Abe; T. Usui; T. R. Ireland; M. Fujimoto; T. Yamada; M. Arakawa; H. C. Connolly; A. Fujii; S. Hasegawa; N. Hirata; N. Hirata; C. Hirose; S. Hosoda; Y. Iijima; H. Ikeda; M. Ishiguro; Y. Ishihara; T. Iwata; S. Kikuchi; K. Kitazato; D. S. Lauretta; G. Libourel; B. Marty; K. Matsumoto; T. Michikami; Y. Mimasu; A. Miura; O. Mori; K. Nakamura-Messenger; N. Namiki; A. N. Nguyen; L. R. Nittler; H. Noda; R. Noguchi; N. Ogawa; G. Ono; M. Ozaki; H. Senshu; T. Shimada; Y. Shimaki; K. Shirai; S. Soldini; T. Takahashi; Y. Takei; H. Takeuchi; R. Tsukizaki; K. Wada; Y. Yamamoto; K. Yoshikawa; K. Yumoto; M. E. Zolensky; S. Nakazawa; F. Terui; S. Tanaka; T. Saiki; M. Yoshikawa; S. Watanabe; Y. Tsuda
    Science American Association for the Advancement of Science (AAAS) 375 (6584) 1011 - 1016 0036-8075 2022/03 [Refereed]
     
    The Hayabusa2 spacecraft investigated the C-type (carbonaceous) asteroid (162173) Ryugu. The mission performed two landing operations to collect samples of surface and subsurface material, the latter exposed by an artificial impact. We present images of the second touchdown site, finding that ejecta from the impact crater was present at the sample location. Surface pebbles at both landing sites show morphological variations ranging from rugged to smooth, similar to Ryugu’s boulders, and shapes from quasi-spherical to flattened. The samples were returned to Earth on 6 December 2020. We describe the morphology of >5 grams of returned pebbles and sand. Their diverse color, shape, and structure are consistent with the observed materials of Ryugu; we conclude that they are a representative sample of the asteroid.
  • Tatsuhiro Michikami; Axel Hagermann; Tomokatsu Morota; Yasuhiro Yokota; Seitaro Urakawa; Hiroyuki Okamura; Naoya Tanabe; Koki Yumoto; Tatsuki Ebihara; Yuichiro Cho; Carolyn M. Ernst; Masahiko Hayakawa; Masatoshi Hirabayashi; Naru Hirata; Chikatoshi Honda; Rie Honda; Shingo Kameda; Masanori Kanamaru; Hiroshi Kikuchi; Shota Kikuchi; Toru Kouyama; Moe Matsuoka; Hideaki Miyamoto; Takaaki Noguchi; Rina Noguchi; Kazunori Ogawa; Tatsuaki Okada; Naoya Sakatani; Sho Sasaki; Hirotaka Sawada; Chiho Sugimoto; Hidehiko Suzuki; Satoshi Tanaka; Eri Tatsumi; Akira Tsuchiyama; Yuichi Tsuda; Sei-ichiro Watanabe; Manabu Yamada; Makoto Yoshikawa; Kazuo Yoshioka; Seiji Sugita
    Icarus Elsevier BV 115007 - 115007 0019-1035 2022/03 [Refereed]
  • Toru Yada; Masanao Abe; Tatsuaki Okada; Aiko Nakato; Kasumi Yogata; Akiko Miyazaki; Kentaro Hatakeda; Kazuya Kumagai; Masahiro Nishimura; Yuya Hitomi; Hiromichi Soejima; Miwa Yoshitake; Ayako Iwamae; Shizuho Furuya; Masayuki Uesugi; Yuzuru Karouji; Tomohiro Usui; Tasuku Hayashi; Daiki Yamamoto; Ryota Fukai; Seiji Sugita; Yuichiro Cho; Koki Yumoto; Yuna Yabe; Jean-Pierre Bibring; Cedric Pilorget; Vincent Hamm; Rosario Brunetto; Lucie Riu; Lionel Lourit; Damien Loizeau; Guillaume Lequertier; Aurelie Moussi-Soffys; Shogo Tachibana; Hirotaka Sawada; Ryuji Okazaki; Yoshinori Takano; Kanako Sakamoto; Yayoi N. Miura; Hajime Yano; Trevor R. Ireland; Tetsuya Yamada; Masaki Fujimoto; Kohei Kitazato; Noriyuki Namiki; Masahiko Arakawa; Naru Hirata; Hisayoshi Yurimoto; Tomoki Nakamura; Takaaki Noguchi; Hikaru Yabuta; Hiroshi Naraoka; Motoo Ito; Eizo Nakamura; Kentaro Uesugi; Katsura Kobayashi; Tatsuhiro Michikami; Hiroshi Kikuchi; Naoyuki Hirata; Yoshiaki Ishihara; Koji Matsumoto; Hirotomo Noda; Rina Noguchi; Yuri Shimaki; Kei Shirai; Kazunori Ogawa; Koji Wada; Hiroki Senshu; Yukio Yamamoto; Tomokatsu Morota; Rie Honda; Chikatoshi Honda; Yasuhiro Yokota; Moe Matsuoka; Naoya Sakatani; Eri Tatsumi; Akira Miura; Manabu Yamada; Atsushi Fujii; Chikako Hirose; Satoshi Hosoda; Hitoshi Ikeda; Takahiro Iwata; Shota Kikuchi; Yuya Mimasu; Osamu Mori; Naoko Ogawa; Go Ono; Takanobu Shimada; Stefania Soldini; Tadateru Takahashi; Yuto Takei; Hiroshi Takeuchi; Ryudo Tsukizaki; Kent Yoshikawa; Fuyuto Terui; Satoru Nakazawa; Satoshi Tanaka; Takanao Saiki; Makoto Yoshikawa; Sei-ichiro Watanabe; Yuichi Tsuda
    Nature Astronomy Springer Science and Business Media LLC 6 (2) 214 - 220 2397-3366 2022/02 [Refereed]
     
    Abstract C-type asteroids1 are considered to be primitive small Solar System bodies enriched in water and organics, providing clues to the origin and evolution of the Solar System and the building blocks of life. C-type asteroid 162173 Ryugu has been characterized by remote sensing2–7 and on-asteroid measurements8,9 with Hayabusa2 (ref. 10). However, the ground truth provided by laboratory analysis of returned samples is invaluable to determine the fine properties of asteroids and other planetary bodies. We report preliminary results of analyses on returned samples from Ryugu of the particle size distribution, density and porosity, spectral properties and textural properties, and the results of a search for Ca–Al-rich inclusions (CAIs) and chondrules. The bulk sample mainly consists of rugged and smooth particles of millimetre to submillimetre size, confirming that the physical and chemical properties were not altered during the return from the asteroid. The power index of its size distribution is shallower than that of the surface boulder observed on Ryugu11, indicating differences in the returned Ryugu samples. The average of the estimated bulk densities of Ryugu sample particles is 1,282 ± 231 kg m−3, which is lower than that of meteorites12, suggesting a high microporosity down to the millimetre scale, extending centimetre-scale estimates from thermal measurements5,9. The extremely dark optical to near-infrared reflectance and spectral profile with weak absorptions at 2.7 and 3.4 μm imply a carbonaceous composition with indigenous aqueous alteration, matching the global average of Ryugu3,4 and confirming that the sample is representative of the asteroid. Together with the absence of submillimetre CAIs and chondrules, these features indicate that Ryugu is most similar to CI chondrites but has lower albedo, higher porosity and more fragile characteristics.
  • Yasuhiro Yokota; Rie Honda; Eri Tatsumi; Deborah Domingue; Stefan Schröder; Moe Matsuoka; Tomokatsu Morota; Naoya Sakatani; Shingo Kameda; Toru Kouyama; Manabu Yamada; Chikatoshi Honda; Masahiko Hayakawa; Yuichiro Cho; Tatsuhiro Michikami; Hidehiko Suzuki; Kazuo Yoshioka; Hirotaka Sawada; Kazunori Ogawa; Kouki Yumoto; Seiji Sugita
    Planetary Science Journal 2 (5) 2021/10 [Refereed]
     
    On 2019 January 8, the Telescopic Optical Navigation Camera (ONC-T) on board the Hayabusa2 spacecraft observed the Cb-type asteroid 162173 Ryugu under near-opposition illumination and viewing conditions from approximately 20 km in distance. Although opposition observations have never been used for mapping purposes of a planetary body, we found three advantages for mapping under these conditions: (1) images are free of topographic shadows, (2) the reflectance is nearly independent of the orientation of the surface, and (3) spurious color artifacts that may appear near shadowed terrain are avoided. We present normal albedo maps, one for each of the seven filters (0.40–0.95 μm), using an empirical photometric correction. Global coverage of Ryugu is 99.4%. The 0.55 μm band average normal albedo is 4.06% ± 0.10%. Various spectral variations are derived from these maps. Spectral features of regions and boulders are quantified by examining the normal albedo-derived spectral slope and UV index (spectral slope from visible to ultraviolet wavelength) value. In terms of space weathering, three spectral characteristics are observed over the majority of Ryugu: (1) reddening, (2) increases in reflectance at ultraviolet wavelengths compared to visible, and (3) darkening. By contrast, the bright boulders (“type 3”) show a different trend, with wide variations in the 0.95 μm albedo and UV index. Finally, principal component analysis (PCA) comparisons with other asteroids strongly suggest that the main components of Ryugu belong to the B-Cb-type populations. The PCA feature of the fresh material on Ryugu is close to the Eulalia family.
  • Naoya Tanabe; Yuichiro Cho; Eri Tatsumi; Tatsuki Ebihara; Koki Yumoto; Tatsuhiro Michikami; Hideaki Miyamoto; Tomokatsu Morota; Chikatoshi Honda; Patrick Michel; Katharina Otto; Olivier Barnouin; Kazuo Yoshioka; Hirotaka Sawada; Yasuhiro Yokota; Naoya Sakatani; Masahiro Hayakawa; Rie Honda; Shingo Kameda; Moe Matsuoka; Manabu Yamada; Toru Kouyama; Hidehiko Suzuki; Kazunori Ogawa; Seiji Sugita
    Planetary and Space Science Elsevier BV 204 105249 - 105249 0032-0633 2021/09 [Refereed]
     
    Recent asteroid missions have revealed that many sub-kilometer asteroids are rubble piles. Large parts of their surfaces are covered with boulders larger than tens of centimeters. An evaluation of the abundance and size distribution of boulders provides clues to understand surface processes on boulder-covered asteroids. Here we report a new method that automatically measures the abundance of small boulders (sub-pixel to a few pixels), whose boundaries cannot be recognized with visual inspection, by quantifying the surface radiance variation that occurs during the spinning of the asteroid. After validating our approach with previous boulder counting data, we apply this method to images of the asteroids Ryugu and Itokawa, which were visited by JAXA's Hayabusa and Hayabusa2, and obtain a global distribution of the boulders larger than 0.75–3 ​m, which corresponds to 1.5–6 pixels. We find that the boulder number density of this size range is smaller (1) on the western bulge than on the eastern hemisphere and (2) on the equatorial ridge than on the higher latitudes, both of which exceed the number density of boulders ​> ​5 ​m by an order of magnitude. The boulder size distribution at 1.25–20 ​m shows that the boulders smaller than 1 ​m are more abundant at the equator than at mid-latitudes, while those larger than 1 ​m in diameter are more abundant at mid-latitudes than at the equator. This contrast suggests size-dependent migration of boulders in the latitudinal direction. We also find that the typical boulder size (the size reaching the cumulative areal coverage of 50%) is 1.9 ​m at the equatorial region (10°S-10°N) while it is 2.6 ​m at mid-latitudes (40°S-50°S, 40°N-50°N). The typical boulder size is also smaller in the western bulge (2.0–2.2 ​m). We construct global maps of the power-law index of the size frequency distribution of boulders and find minor variations over the entire surface of Ryugu (−2.53 ​± ​0.03) for boulders larger than 1.25 ​m. This small variation suggests homogeneous size sorting processes on Ryugu. Surface roughness does not show a significant correlation with the v-band albedo but shows a high anti-correlation (R ​= ​−0.73) with the current geological slope on the eastern hemisphere. Our method is useful enhancement of smooth area detection and boulder distribution characterization that will be applicable to other planetary explorations in the future, including those of Phobos and other asteroids.
  • Chiho Sugimoto; Eri Tatsumi; Yuichiro Cho; Tomokatsu Morota; Rie Honda; Shingo Kameda; Yosuhiro Yokota; Koki Yumoto; Minami Aoki; Daniella N. DellaGiustina; Tatsuhiro Michikami; Takahiro Hiroi; Deborah L. Domingue; Patrick Michel; Stefan E. Schröder; Tomoki Nakamura; Manabu Yamada; Naoya Sakatani; Toru Kouyama; Chikatoshi Honda; Masahiko Hayakawa; Moe Matsuoka; Hidehiko Suzuki; Kazuo Yoshioka; Kazunori Ogawa; Hirotaka Sawada; Masahiko Arakawa; Takanao Saiki; Hiroshi Imamura; Yasuhiko Takagi; Hajime Yano; Kei Shirai; Chisato Okamoto; Yuichi Tsuda; Satoru Nakazawa; Yuichi Iijima; Seiji Sugita
    Icarus Elsevier BV 369 114591 - 114591 0019-1035 2021/06 [Refereed]
     
    Many small boulders with reflectance values higher than 1.5 times the average reflectance have been found on the near-Earth asteroid 162,173 Ryugu. Based on their visible wavelength spectral differences, Tatsumi et al. (2021, Nature Astronomy, 5, doi:10.1038/s41550-020-1179-z) defined two bright boulder classes: C-type and S- type. These two classifications of bright boulders have different size distributions and spectral trends. In this study, we measured the spectra of 79 bright boulders and investigated their detailed spectral properties. Analyses obtained a number of important results. First, S-type bright boulders on Ryugu have spectra that are similar to those found for two different ordinary chondrites with different initial spectra that have been experimentally space weathered the same way. This suggests that there may be two populations of S-type bright boulders on Ryugu, perhaps originating from two different impactors that hit Ryugu's parent body. Second, the model space-weathering ages of meter-size S-type bright boulders, based on spectral change rates derived in previous experimentally irradiated ordinary chondrites, are 10(6)-10(6) years, which is consistent with the crater retention age (<10(6) years) of the similar to 1-m deep surface layer on Ryugu. This agreement strongly suggests that Ryugu's surface is extremely young, implying that the samples acquired from Ryugu's surface should be fresh. Third, the lack of a serpentine absorption in the S-type clast embedded in one of the large brecciated boulders indicates that fragmentation and cementation that created the breccias occurred after the termination of aqueous alteration. Fourth, C-type bright boulders exhibit a continuous spectral trend similar to the heating track of low-albedo carbonaceous chondrites, such as CM and CI. Other processes, such as space weathering and grain size effects, cannot primarily account for their spectral variation. Furthermore, the distribution of the spectra of general dark boulders, which constitute >99.9% of Ryugu's volume, is located along the trend line in slope/UV-index diagram that is occupied by C-type bright boulders. These results indicate that thermal metamorphism might be the dominant cause for the spectral variety among the C-type bright boulders on Ryugu and that general boulders on Ryugu may have experienced thermal metamorphism under a much narrower range of conditions than the C-type bright boulders. This supports the hypothesis that Ryugu's parent body experienced uniform heating due to radiogenic energy rather than impact heating.
  • Chiho Sugimoto; Eri Tatsumi; Yuichiro Cho; Tomokatsu Morota; Rie Honda; Shingo Kameda; Yosuhiro Yokota; Koki Yumoto; Minami Aoki; Daniella N. DellaGiustina; Tatsuhiro Michikami; Takahiro Hiroi; Deborah L. Domingue; Patrick Michel; Stefan E. Schröder; Tomoki Nakamura; Manabu Yamada; Naoya Sakatani; Toru Kouyama; Chikatoshi Honda; Masahiko Hayakawa; Moe Matsuoka; Hidehiko Suzuki; Kazuo Yoshioka; Kazunori Ogawa; Hirotaka Sawada; Masahiko Arakawa; Takanao Saiki; Hiroshi Imamura; Yasuhiko Takagi; Hajime Yano; Kei Shirai; Chisato Okamoto; Yuichi Tsuda; Satoru Nakazawa; Yuichi Iijima; Seiji Sugita
    Icarus Elsevier BV 369 114529 - 114529 0019-1035 2021/05 [Refereed]
     
    The near-Earth asteroid (162173) Ryugu displays a Cb-type average spectrum and a very low average normal albedo of 0.04. Although the majority of boulders on Ryugu have reflectance spectra and albedo similar to the Ryugu average, a small fraction of boulders exhibit anomalously high albedo and distinctively different spectra. A previous study (Tatsumi et al., 2021Nature Astronomy, 5, doi:https://doi.org/10.1038/s41550-020-1179-z) based on the 2.7-km observations and a series of low-altitude (down to 68 m) descent observations conducted prior to the first touchdown have shown that the spectra of these anomalous boulders can be classified into two distinct groups corresponding to S and C type asteroids. The former originate most likely from an impactor that collided with Ryugu's parent body, whereas the latter may be from portions of Ryugu's parent body that experienced a different temperature history than experienced by the majority of boulder materials. In this study, we analyzed images captured after the first touchdown to determine the quantitative properties of these bright boulders on Ryugu. We measured the sizes of more than a thousand bright boulders and characterized the morphologic properties of the largest ones. Analyses revealed many properties of bright boulders important for the evolution of Ryugu and its parent body. First, the size-frequency distributions of S-type and C-type bright boulders follow a power law with exponents of 1.6 +/- 1.3 and 3.0 +/- 0.7, respectively. Based on these size-frequency distributions, we obtained the ratios of the total volume and surface area of S-type bright boulders to those of average dark boulders on the Ryugu's surface, that is, 7.1(-5.0)(+6.3) x 10(-6) and 1.5(-1.2)(+3.2) x 10(-6), respectively, over the diameter range of 0.3 to 3 m. Similarly, the ratio of the total volume and surface area of C-type bright boulders to those of average dark boulders are 4.4(-2.2)(+14.0) x 10(-5) and 1.3(-1.1)(+9.8) x 10(-3), respectively, at a diameter range of 2 cm to 2 m. Second, the number density of bright boulders inside the artificial crater newly made by the Small Carry-on Impactor (SCI) experiment agrees with the outside number density within a factor of two. Third, many of the bright boulders are embedded in a larger substrate boulder, suggesting that they have experienced mixing and conglomeration with darker fragments on Ryugu's parent body, rather than gently landing on Ryugu during or after its formation by reaccumulation. This observation is consistent with the hypothesis that S-type bright boulders were likely mixed during and/or before a catastrophic disruption. C-type bright boulders embedded in substrate boulders suggests a brecciation process after thermal metamorphism. Furthermore, the embedding of S-type clasts in substrate boulders suggests that brecciation did indeed occur even after a large-scale impact on the parent body. If the brecciation on the Ryugu's parent body occurred over such a long period or over many stages of its evolution, breccias may end up being the dominant constituent materials on Ryugu's parent body. Moreover, the preponderance of breccias may contribute to the globally low thermal inertia of Ryugu.
  • Yuichiro Cho; Tomokatsu Morota; Masanori Kanamaru; Naofumi Takaki; Koki Yumoto; Carolyn M. Ernst; Masatoshi Hirabayashi; Olivier S. Barnouin; Eri Tatsumi; Katharina A. Otto; Nicole Schmitz; Roland J Wagner; Ralf Jaumann; Hideaki Miyamoto; Hiroshi Kikuchi; Ryodo Hemmi; Rie Honda; Shingo Kameda; Yasuhiro Yokota; Toru Kouyama; Hidehiko Suzuki; Manabu Yamada; Naoya Sakatani; Chikatoshi Honda; Masahiko Hayakawa; Kazuo Yoshioka; Moe Matsuoka; Tatsuhiro Michikami; Naru Hirata; Hirotaka Sawada; Kazunori Ogawa; Seiji Sugita
    Wiley 2021/04 [Refereed]
  • Tatsuhiro Michikami; Axel Hagermann
    Icarus Elsevier BV 357 114282 - 114282 0019-1035 2021/03 [Refereed]
  • Matthias Grott; Jens Biele; Patrick Michel; Seiji Sugita; Stefan Schröder; Naoya Sakatani; Wladimir Neumann; Shingo Kameda; Tatsuhiro Michikami; Chikatoshi Honda
    Journal of Geophysical Research: Planets American Geophysical Union ({AGU}) 125 (12) 2169-9097 2020/12 [Refereed]
     
    Rubble pile asteroids such as (162173) Ryugu have large bulk porosities, which are believed to result from void spaces in between the constituent boulders (macroporosity) as well as void spaces within the boulders themselves (microporosity). In general, both macroporosity and microporosity are estimated based on comparisons between the asteroid bulk density and both the bulk and grain density of meteorite analogs, and relatively large macroporosities are usually obtained. Here we use semiempirical models for the macroporosity of multicomponent mixtures to determine Ryugu's macroporosity based on the observed size-frequency distribution (SFD) of boulders on the surface. We find that Ryugu's macroporosity can be significantly smaller than usually assumed, as the observed SFD allows for an efficient packing of boulders, resulting in a macroporosity of 16% +/- 3%. Therefore, we confirm that Ryugu's high bulk porosity is a direct consequence of a very large boulder microporosity. Furthermore, using estimates of boulder microporosity of around 50% as derived from in situ measurements, the average grain density in boulders is 2,848 +/- 152 kg m(-3), similar to values obtained for CM and the Tagish lake meteorites. Ryugu's bulk porosity corresponding to the above values is 58%. Thus, the macroporosity of rubble pile asteroids may have been systematically overestimated in the past.
  • Shota Kikuchi; Sei-ichiro Watanabe; Takanao Saiki; Hikaru Yabuta; Seiji Sugita; Tomokatsu Morota; Naru Hirata; Naoyuki Hirata; Tatsuhiro Michikami; Chikatoshi Honda; Yashuhiro Yokota; Rie Honda; Naoya Sakatani; Tatsuaki Okada; Yuri Shimaki; Koji Matsumoto; Rina Noguchi; Yuto Takei; Fuyuto Terui; Naoko Ogawa; Kent Yoshikawa; Go Ono; Yuya Mimasu; Hirotaka Sawada; Hitoshi Ikeda; Chikako Hirose; Tadateru Takahashi; Atsushi Fujii; Tomohiro Yamaguchi; Yoshiaki Ishihara; Tomoki Nakamura; Kohei Kitazato; Koji Wada; Shogo Tachibana; Eri Tatsumi; Moe Matsuoka; Hiroki Senshu; Shingo Kameda; Toru Kouyama; Manabu Yamada; Kei Shirai; Yuichiro Cho; Kazunori Ogawa; Yukio Yamamoto; Akira Miura; Takahiro Iwata; Noriyuki Namiki; Masahiko Hayakawa; Masanao Abe; Satoshi Tanaka; Makoto Yoshikawa; Satoru Nakazawa; Yuichi Tsuda
    Space Science Reviews Springer Science and Business Media LLC 216 (7) 0038-6308 2020/10 [Refereed]
  • E. Tatsumi; C. Sugimoto; L. Riu; S. Sugita; T. Nakamura; T. Hiroi; T. Morota; M. Popescu; T. Michikami; K. Kitazato; M. Matsuoka; S. Kameda; R. Honda; M. Yamada; N. Sakatani; T. Kouyama; Y. Yokota; C. Honda; H. Suzuki; Y. Cho; K. Ogawa; M. Hayakawa; H. Sawada; K. Yoshioka; C. Pilorget; M. Ishida; D. Domingue; N. Hirata; S. Sasaki; J. de León; M. A. Barucci; P. Michel; M. Suemitsu; T. Saiki; S. Tanaka; F. Terui; S. Nakazawa; S. Kikuchi; T. Yamaguchi; N. Ogawa; G. Ono; Y. Mimasu; K. Yoshikawa; T. Takahashi; Y. Takei; A. Fujii; Y. Yamamoto; T. Okada; C. Hirose; S. Hosoda; O. Mori; T. Shimada; S. Soldini; R. Tsukizaki; T. Mizuno; T. Iwata; H. Yano; M. Ozaki; M. Abe; M. Ohtake; N. Namiki; S. Tachibana; M. Arakawa; H. Ikeda; M. Ishiguro; K. Wada; H. Yabuta; H. Takeuchi; Y. Shimaki; K. Shirai; N. Hirata; Y. Iijima; Y. Tsuda; S. Watanabe; M. Yoshikawa
    Nature Astronomy Springer Science and Business Media {LLC} 5 (1) 39 - 45 2020/09 [Refereed]
  • T. Morota; S. Sugita; Y. Cho; M. Kanamaru; E. Tatsumi; N. Sakatani; R. Honda; N. Hirata; H. Kikuchi; M. Yamada; Y. Yokota; S. Kameda; M. Matsuoka; H. Sawada; C. Honda; T. Kouyama; K. Ogawa; H. Suzuki; K. Yoshioka; M. Hayakawa; N. Hirata; M. Hirabayashi; H. Miyamoto; T. Michikami; T. Hiroi; R. Hemmi; O. S. Barnouin; C. M. Ernst; K. Kitazato; T. Nakamura; L. Riu; H. Senshu; H. Kobayashi; S. Sasaki; G. Komatsu; N. Tanabe; Y. Fujii; T. Irie; M. Suemitsu; N. Takaki; C. Sugimoto; K. Yumoto; M. Ishida; H. Kato; K. Moroi; D. Domingue; P. Michel; C. Pilorget; T. Iwata; M. Abe; M. Ohtake; Y. Nakauchi; K. Tsumura; H. Yabuta; Y. Ishihara; R. Noguchi; K. Matsumoto; A. Miura; N. Namiki; S. Tachibana; M. Arakawa; H. Ikeda; K. Wada; T. Mizuno; C. Hirose; S. Hosoda; O. Mori; T. Shimada; S. Soldini; R. Tsukizaki; H. Yano; M. Ozaki; H. Takeuchi; Y. Yamamoto; T. Okada; Y. Shimaki; K. Shirai; Y. Iijima; H. Noda; S. Kikuchi; T. Yamaguchi; N. Ogawa; G. Ono; Y. Mimasu; K. Yoshikawa; T. Takahashi; Y. Takei; A. Fujii; S. Nakazawa; F. Terui; S. Tanaka; M. Yoshikawa; T. Saiki; S. Watanabe; Y. Tsuda
    Science American Association for the Advancement of Science (AAAS) 368 (6491) 654 - 659 0036-8075 2020/05 [Refereed]
     
    The near-Earth asteroid (162173) Ryugu is thought to be a primitive carbonaceous object that contains hydrated minerals and organic molecules. We report sample collection from Ryugu’s surface by the Hayabusa2 spacecraft on 21 February 2019. Touchdown images and global observations of surface colors are used to investigate the stratigraphy of the surface around the sample location and across Ryugu. Latitudinal color variations suggest the reddening of exposed surface material by solar heating and/or space weathering. Immediately after touchdown, Hayabusa2’s thrusters disturbed dark, fine grains that originate from the redder materials. The stratigraphic relationship between identified craters and the redder material indicates that surface reddening occurred over a short period of time. We suggest that Ryugu previously experienced an orbital excursion near the Sun.
  • Tatsuaki Okada; Tetsuya Fukuhara; Satoshi Tanaka; Makoto Taguchi; Takehiko Arai; Hiroki Senshu; Naoya Sakatani; Yuri Shimaki; Hirohide Demura; Yoshiko Ogawa; Kentaro Suko; Tomohiko Sekiguchi; Toru Kouyama; Jun Takita; Tsuneo Matsunaga; Takeshi Imamura; Takehiko Wada; Sunao Hasegawa; Jörn Helbert; Thomas G. Müller; Axel Hagermann; Jens Biele; Matthias Grott; Maximilian Hamm; Marco Delbo; Naru Hirata; Naoyuki Hirata; Yukio Yamamoto; Seiji Sugita; Noriyuki Namiki; Kohei Kitazato; Masahiko Arakawa; Shogo Tachibana; Hitoshi Ikeda; Masateru Ishiguro; Koji Wada; Chikatoshi Honda; Rie Honda; Yoshiaki Ishihara; Koji Matsumoto; Moe Matsuoka; Tatsuhiro Michikami; Akira Miura; Tomokatsu Morota; Hirotomo Noda; Rina Noguchi; Kazunori Ogawa; Kei Shirai; Eri Tatsumi; Hikaru Yabuta; Yasuhiro Yokota; Manabu Yamada; Masanao Abe; Masahiko Hayakawa; Takahiro Iwata; Masanobu Ozaki; Hajime Yano; Satoshi Hosoda; Osamu Mori; Hirotaka Sawada; Takanobu Shimada; Hiroshi Takeuchi; Ryudo Tsukizaki; Atsushi Fujii; Chikako Hirose; Shota Kikuchi; Yuya Mimasu; Naoko Ogawa; Go Ono; Tadateru Takahashi; Yuto Takei; Tomohiro Yamaguchi; Kent Yoshikawa; Fuyuto Terui; Takanao Saiki; Satoru Nakazawa; Makoto Yoshikawa; Seiichiro Watanabe; Yuichi Tsuda
    Nature Springer Science and Business Media LLC 579 (7800) 518 - 522 0028-0836 2020/03 [Refereed]
     
    Carbonaceous (C-type) asteroids1 are relics of the early Solar System that have preserved primitive materials since their formation approximately 4.6 billion years ago. They are probably analogues of carbonaceous chondrites2,3 and are essential for understanding planetary formation processes. However, their physical properties remain poorly known because carbonaceous chondrite meteoroids tend not to survive entry to Earth's atmosphere. Here we report on global one-rotation thermographic images of the C-type asteroid 162173 Ryugu, taken by the thermal infrared imager (TIR)4 onboard the spacecraft Hayabusa25, indicating that the asteroid's boulders and their surroundings have similar temperatures, with a derived thermal inertia of about 300 J m-2 s-0.5 K-1 (300 tiu). Contrary to predictions that the surface consists of regolith and dense boulders, this low thermal inertia suggests that the boulders are more porous than typical carbonaceous chondrites6 and that their surroundings are covered with porous fragments more than 10 centimetres in diameter. Close-up thermal images confirm the presence of such porous fragments and the flat diurnal temperature profiles suggest a strong surface roughness effect7,8. We also observed in the close-up thermal images boulders that are colder during the day, with thermal inertia exceeding 600 tiu, corresponding to dense boulders similar to typical carbonaceous chondrites6. These results constrain the formation history of Ryugu: the asteroid must be a rubble pile formed from impact fragments of a parent body with microporosity9 of approximately 30 to 50 per cent that experienced a low degree of consolidation. The dense boulders might have originated from the consolidated innermost region or they may have an exogenic origin. This high-porosity asteroid may link cosmic fluffy dust to dense celestial bodies10.
  • Tatsuhiro Michikami; Axel Hagermann; Akira Tsuchiyama; Hirotaka Yamaguchi; Terunori Irie; Keita Nomura; Osamu Sasaki; Michihiko Nakamura; Satoshi Okumura; Sunao Hasegawa
    Planetary and Space Science Elsevier BV 177 (104690 (14pp.)) 104690 - 104690 0032-0633 2019/11 [Refereed]
  • Tatsuhiro Michikami; Chikatoshi Honda; Hideaki Miyamoto; Masatoshi Hirabayashi; Axel Hagermann; Terunori Irie; Keita Nomura; Carolyn M. Ernst; Masaki Kawamura; Kiichi Sugimoto; Eri Tatsumi; Tomokatsu Morota; Naru Hirata; Takaaki Noguchi; Yuichiro Cho; Shingo Kameda; Toru Kouyama; Yasuhiro Yokota; Rina Noguchi; Masahiko Hayakawa; Naoyuki Hirata; Rie Honda; Moe Matsuoka; Naoya Sakatani; Hidehiko Suzuki; Manabu Yamada; Kazuo Yoshioka; Hirotaka Sawada; Ryodo Hemmi; Hiroshi Kikuchi; Kazunori Ogawa; Sei ichiro Watanabe; Satoshi Tanaka; Makoto Yoshikawa; Yuichi Tsuda; Seiji Sugita
    Icarus 331 179 - 191 0019-1035 2019/10 [Refereed]
     
    © 2019 The Authors In 2018, the Japanese spacecraft Hayabusa2, arrived at the small asteroid Ryugu. The surface of this C-type asteroid is covered with numerous boulders whose size and shape distributions are investigated in this study. Using a few hundred Optical Navigation Camera (ONC) images with a pixel scale of approximately 0.65 m, we focus on boulders greater than 5 m in diameter. Smaller boulders are also considered using five arbitrarily chosen ONC close-up images with pixel scales ranging from 0.7 to 6 cm. Across the entire surface area (~2.7 km2) of Ryugu, nearly 4400 boulders larger than 5 m were identified. Boulders appear to be uniformly distributed across the entire surface, with some slight differences in latitude and longitude. At ~50 km−2, the number density of boulders larger than 20 m is twice as large as on asteroid Itokawa (or Bennu). The apparent shapes of Ryugu's boulders resemble laboratory impact fragments, with larger boulders being more elongated. The ratio of the total volume of boulders larger than 5 m to the total excavated volume of craters larger than 20 m on Ryugu can be estimated to be ~94%, which is comparatively high. These observations strongly support the hypothesis that most boulders found on Ryugu resulted from the catastrophic disruption of Ryugu's larger parent body, as described in previous papers (Watanabe et al., 2019; Sugita et al., 2019). The cumulative size distribution of boulders larger than 5 m has a power-index of −2.65 ± 0.05, which is comparatively shallow compared with other asteroids visited by spacecraft. For boulders smaller than 4 m, the power-index is even shallower and ranges from −1.65 ± 0.05 to −2.01 ± 0.06. This particularly shallow power-index implies that some boulders are buried in Ryugu's regolith. Based on our observations, we suggest that boulders near the equator might have been buried by the migration of finer material and, as a result, the number density of boulders larger than 5 m in the equatorial region is lower than at higher latitudes.
  • S Watanabe; M Hirabayashi; N Hirata; Na Hirata; R Noguchi; Y Shimaki; H Ikeda; E Tatsumi; M Yoshikawa; S Kikuchi; H Yabuta; T Nakamura; S Tachibana; Y Ishihara; T Morota; K Kitazato; N Sakatani; K Matsumoto; K Wada; H Senshu; C Honda; T Michikami; H Takeuchi; T Kouyama; R Honda; S Kameda; T Fuse; H Miyamoto; G Komatsu; S Sugita; T Okada; N Namiki; M Arakawa; M Ishiguro; M Abe; R Gaskell; E Palmer; O S Barnouin; P Michel; A S French; J W McMahon; D J Scheeres; P A Abell; Y Yamamoto; S Tanaka; K Shirai; M Matsuoka; M Yamada; Y Yokota; H Suzuki; K Yoshioka; Y Cho; S Tanaka; N Nishikawa; T Sugiyama; H Kikuchi; R Hemmi; T Yamaguchi; N Ogawa; G Ono; Y Mimasu; K Yoshikawa; T Takahashi; Y Takei; A Fujii; C Hirose; T Iwata; M Hayakawa; S Hosoda; O Mori; H Sawada; T Shimada; S Soldini; H Yano; R Tsukizaki; M Ozaki; Y Iijima; K Ogawa; M Fujimoto; T-M Ho; A Moussi; R Jaumann; J-P Bibring; C Krause; F Terui; T Saiki; S Nakazawa; Y Tsuda
    Science (New York, N.Y.) 364 (6437) 268 - 272 2019/04 [Refereed]
     
    The Hayabusa2 spacecraft arrived at the near-Earth carbonaceous asteroid 162173 Ryugu in 2018. We present Hayabusa2 observations of Ryugu's shape, mass, and geomorphology. Ryugu has an oblate "spinning top" shape, with a prominent circular equatorial ridge. Its bulk density, 1.19 ± 0.02 grams per cubic centimeter, indicates a high-porosity (>50%) interior. Large surface boulders suggest a rubble-pile structure. Surface slope analysis shows Ryugu's shape may have been produced from having once spun at twice the current rate. Coupled with the observed global material homogeneity, this suggests that Ryugu was reshaped by centrifugally induced deformation during a period of rapid rotation. From these remote-sensing investigations, we identified a suitable sample collection site on the equatorial ridge.
  • Seitaro Urakawa; Ryou Ohsawa; Shigeyuki Sako; Shin-ichiro Okumura; Yuri Sakurai; Jun Takahashi; Kazuyoshi Imamura; Hiroyuki Naito; Fumitake Watanabe; Ryoma Nagayoshi; Yasuhiko Murakami; Ryo Okazaki; Tomohiko Sekiguchi; Masateru Ishiguro; Tatsuhiro Michikami; Makoto Yoshikawa
    The Astronomical Journal IOP PUBLISHING LTD 157 (155) 0004-6256 2019/04 [Refereed]
     
    We present visible and near-infrared observations of a near-Earth object (NEO), 2012 TC4. The NEO 2012 TC4 approached close to Earth at a distance of about 50,000 km in 2017 October. This close approach provided a practical exercise for planetary defense. This apparition was also an appropriate opportunity to investigate 2012 TC4, which is a monolithic asteroid. We conducted the observation campaign of 2012 TC4 using six small- and medium-sized telescopes. The multiband photometry analysis showed the taxonomic class of 2012 TC4 to be an X type. In particular, we successfully obtained the high time resolution light curve of 2012 TC4 with the Tomo-e Gozen camera, which is the world's first wide-field CMOS camera, mounted on the 1.05 m Schmidt telescope at Kiso Observatory. The shape and rotational motion models of 2012 TC4 were derived from the light curve. When 2012 TC4 was assumed to be a triaxial ellipsoid, the rotational and precession periods were 8.47 +/- 0.01 minutes and 12.25 +/- 0.01 minutes, respectively, with the long-axis mode. This indicates that 2012 TC4 is a tumbling and monolithic asteroid. The shape models showed the plausible axial lengths to be 6.2 x 8.0 x 14.9 m or 3.3 x 8.0 x 14.3 m. The flattened and elongated shape indicates that 2012 TC4 is a fragment produced by an impact event. We also estimated the excitation timescale, which implied that the impact event happened within similar to 3 x 10(5) yr and 2012 TC4 has a fresh surface.
  • Masatoshi Hirabayashi; Eri Tatsumi; Hideaki Miyamoto; Goro Komatsu; Seiji Sugita; Sei Ichiro Watanabe; Daniel J. Scheeres; Olivier S. Barnouin; Patrick Michel; Chikatoshi Honda; Tatsuhiro Michikami; Yuichiro Cho; Tomokatsu Morota; Naru Hirata; Naoyuki Hirata; Naoya Sakatani; Stephen R. Schwartz; Rie Honda; Yasuhiro Yokota; Shingo Kameda; Hidehiko Suzuki; Toru Kouyama; Masahiko Hayakawa; Moe Matsuoka; Kazuo Yoshioka; Kazunori Ogawa; Hirotaka Sawada; Makoto Yoshikawa; Yuichi Tsuda
    Astrophysical Journal Letters 874 (1) 2041-8205 2019/03 [Refereed]
     
    © 2019. The American Astronomical Society. All rights reserved.. 162173 Ryugu, the target of Hayabusa2, has a round shape with an equatorial ridge, which is known as a spinning top shape. A strong centrifugal force is a likely contributor to Ryugu's top-shaped features. Observations by the Optical Navigation Camera on board Hayabusa2 show a unique longitudinal variation in geomorphology; the western side of this asteroid, later called the western bulge, has a smooth surface and a sharp equatorial ridge, compared to the other side. Here, we propose a structural deformation process that generated the western bulge. Applying the mission-derived shape model, we employ a finite element model technique to analyze the locations that experience structural failure within the present shape. Assuming that materials are uniformly distributed, our model shows the longitudinal variation in structurally failed regions when the spin period is shorter than ∼3.75 hr. Ryugu is structurally intact in the subsurface region of the western bulge while other regions are sensitive to structural failure. We infer that this variation is indicative of the deformation process that occurred in the past, and the western bulge is more relaxed structurally than the other region. Our analysis also shows that this deformation process might occur at a spin period between ∼3.5 and ∼3.0 hr, providing the cohesive strength ranging between ∼4 and ∼10 Pa.
  • Sugita, S.; Honda, R.; Morota, T.; Kameda, S.; Sawada, H.; Tatsumi, E.; Yamada, M.; Honda, C.; Yokota, Y.; Kouyama, T.; Sakatani, N.; Ogawa, K.; Suzuki, H.; Okada, T.; Namiki, N.; Tanaka, S.; Iijima, Y.; Yoshioka, K.; Hayakawa, M.; Cho, Y.; Matsuoka, M.; Hirata, N.; Hirata, N.; Miyamoto, H.; Domingue, D.; Hirabayashi, M.; Nakamura, T.; Hiroi, T.; Michikami, T.; Michel, P.; Ballouz, R.-L.; Barnouin, O. S.; Ernst, C. M.; Schr{\"o}der, S. E.; Kikuchi, H.; Hemmi, R.; Komatsu, G.; Fukuhara, T.; Taguchi, M.; Arai, T.; Senshu, H.; Demura, H.; Ogawa, Y.; Shimaki, Y.; Sekiguchi, T.; M{\"u}ller, T. G.; Hagermann, A.; Mizuno, T.; Noda, H.; Matsumoto, K.; Yamada, R.; Ishihara, Y.; Ikeda, H.; Araki, H.; Yamamoto, K.; Abe, S.; Yoshida, F.; Higuchi, A.; Sasaki, S.; Oshigami, S.; Tsuruta, S.; Asari, K.; Tazawa, S.; Shizugami, M.; Kimura, J.; Otsubo, T.; Yabuta, H.; Hasegawa, S.; Ishiguro, M.; Tachibana, S.; Palmer, E.; Gaskell, R.; Le Corre, L.; Jaumann, R.; Otto, K.; Schmitz, N.; Abell, P. A.; Barucci, M. A.; Zolensky, M. E.; Vilas, F.; Thuillet, F.; Sugimoto, C.; Takaki, N.; Suzuki, Y.; Kamiyoshihara, H.; Okada, M.; Nagata, K.; Fujimoto, M.; Yoshikawa, M.; Yamamoto, Y.; Shirai, K.; Noguchi, R.; Ogawa, N.; Terui, F.; Kikuchi, S.; Yamaguchi, T.; Oki, Y.; Takao, Y.; Takeuchi, H.; Ono, G.; Mimasu, Y.; Yoshikawa, K.; Takahashi, T.; Takei, Y.; Fujii, A.; Hirose, C.; Nakazawa, S.; Hosoda, S.; Mori, O.; Shimada, T.; Soldini, S.; Iwata, T.; Abe, M.; Yano, H.; Tsukizaki, R.; Ozaki, M.; Nishiyama, K.; Saiki, T.; Watanabe, S.; Tsuda, Y.
    Science American Association for the Advancement of Science 364 (6437) 2019 [Refereed]
  • Wada, K.; Grott, M.; Michel, P.; Walsh, K.J.; Barucci, A.M.; Biele, J.; Blum, J.; Ernst, C.M.; Grundmann, J.T.; Gundlach, B.; Hagermann, A.; Hamm, M.; Jutzi, M.; Kim, M.-J.; K{\"u}hrt, E.; Le Corre, L.; Libourel, G.; Lichtenheldt, R.; Maturilli, A.; Messenger, S.R.; Michikami, T.; Miyamoto, H.; Mottola, S.; M{\"u}ller, T.; Nakamura, A.M.; Nittler, L.R.; Ogawa, K.; Okada, T.; Palomba, E.; Sakatani, N.; Schr{\"o}der, S.E.; Senshu, H.; Takir, D.; Zolensky, M.E.
    Progress in Earth and Planetary Science 5 (1) 2018/11 [Refereed]
  • Tatsuhiro Michikami; Tokiyuki Kadokawa; Akira Tsuchiyama; Axel Hagermann; Tsukasa Nakano; Kentaro Uesugi; Sunao Hasegawa
    Icarus Academic Press Inc. 302 109 - 125 1090-2643 2018/03 [Refereed]
     
    In 2010, fine regolith particles on asteroid Itokawa were recovered by the Hayabusa mission. The three-dimensional microstructure of 48 Itokawa particles smaller than 120 µm was examined in previous studies. The shape distribution of Itokawa particles is distributed around the mean values of the axial ratio 2:√2:1, which is similar to laboratory impact fragments larger than several mm created in catastrophic disruptions. Thus, the Itokawa particles are considered to be impact fragments on the asteroid's surface. However, there have never been any laboratory impact experiments investigating the shapes of fine fragments smaller than 120 µm, and little is known about the relation between the shapes of fine fragments and the petrographic textures within those fragments. In this study, in order to investigate the relation between the petrographic textures and the shapes of fine fragments by impacts, the shapes of 2163 fine fragments smaller than 120 µm are examined by synchrotron radiation-based microtomography at SPring-8. Most samples are fine fragments from basalt targets, obtained in previous laboratory impact experiments by Michikami et al. (2016). Moreover, two impacts into L5 chondrite targets were carried out and the shapes of their fine fragments are examined for comparison. The results show that the shape distributions of fine fragments in basalt targets are similar regardless of impact energy per target mass (in contract to the shape distribution of relatively large fragments, which are affected by impact energy), and are similar to those in L5 chondrite targets and Itokawa regolith particles. The physical process producing these fine fragments would be due to multiple rarefaction waves in the target. Besides, the petrographic textures do not significantly affect the shapes of fine fragments in our experiments. On the other hand, according to Molaro et al. (2015), the shapes of the fragments produced by thermal fatigue by the day-night temperature cycles on the asteroid surface are influenced by the petrographic textures. Therefore, we conclude that the Itokawa particles are not the products of thermal fatigue but impact fragments on the asteroid surface.
  • T. Kaku; J. Haruyama; W. Miyake; A. Kumamoto; K. Ishiyama; T. Nishibori; K. Yamamoto; Sarah T. Crites; T. Michikami; Y. Yokota; R. Sood; H. J. Melosh; L. Chappaz; K. C. Howell
    GEOPHYSICAL RESEARCH LETTERS AMER GEOPHYSICAL UNION 44 (20) 10155 - 10161 0094-8276 2017/10 [Refereed]
     
    Intact lunar lava tubes offer a pristine environment to conduct scientific examination of the Moon's composition and potentially serve as secure shelters for humans and instruments. We investigated the SELENE Lunar Radar Sounder (LRS) data at locations close to the Marius Hills Hole (MHH), a skylight potentially leading to an intact lava tube, and found a distinctive echo pattern exhibiting a precipitous decrease in echo power, subsequently followed by a large second echo peak that may be evidence for the existence of a lava tube. The search area was further expanded to 13.00-15.00 degrees N, 301.85-304.01 degrees E around the MHH, and similar LRS echo patterns were observed at several locations. Most of the locations are in regions of underground mass deficit suggested by GRAIL gravity data analysis. Some of the observed echo patterns are along rille A, where the MHH was discovered, or on the southwest underground extension of the rille.
  • Kim, Y.; Ishiguro, M.; Michikami, T.; Nakamura, A.M.
    Astronomical Journal 153 (5) 228 - 238 2017/04 [Refereed]
  • Tatsuhiro Michikami; Axel Hagermann; Tomokatsu Morota; Junichi Haruyama; Sunao Hasegawa
    PLANETARY AND SPACE SCIENCE PERGAMON-ELSEVIER SCIENCE LTD 135 27 - 36 0032-0633 2017/01 [Refereed]
     
    Most impact craters observed on planetary bodies are the results of oblique impacts of meteoroids. To date, however, there have only been very few laboratory oblique impact experiments for analogue targets relevant to the surfaces of extraterrestrial bodies. In particular, there is a lack of laboratory oblique impact experiments into brittle targets with a material strength on the order of 1 MPa, with the exception of ice. A strength on the order of 1 MPa is considered to be the corresponding material strength for the formation of craters in the 100 m size range on the Moon. Impact craters are elliptical if the meteoroid's trajectory is below a certain threshold angle of incidence, and it is known that the threshold angle depends largely on the material strength. Therefore, we examined the threshold angle required to produce elliptical craters in laboratory impact experiments into brittle targets. This work aims to constrain current interpretations of lunar elliptical craters and pit craters with sizes below a hundred meters. We produced mortar targets with compressive strength of 3.2 MPa. A spherical nylon projectile (diameter 7.14 mm) was shot into the target surface at a nominal velocity of 2.3 km/s, with an impact angle of 5 degrees-90 degrees from horizontal. The threshold angle of this experiment ranges from 15 degrees to 20 degrees. We confirmed that our experimental data agree with previous empirical equations in terms of the cratering efficiency and the threshold impact angle. In addition, in order to simulate the relatively large lunar pit craters related to underground cavities, we conducted a second series of experiments under similar impact conditions using targets with an underground rectangular cavity. Size and outline of craters that created a hole are similar to those of craters without a hole. Moreover, when observed from an oblique angle, a crater with a hole has a topography that resembles the lunar pit craters. The relation between the impact velocity of meteoroids on the Moon and the probability of elliptical crater formation was investigated based on our experimental results and an existing empirical equation. The results suggest a distinct possibility that most craters in the 100 m size range on the Moon, given their elliptical shape, originated as secondary craters.
  • HARUYAMA Junichi; NAGAMATSU Aiko; SHIMADA Kazuhito; HASENAKA Toshiaki; MOROTA Tomokatsu; NISHINO Masaki N; HASHIZUME Ko; SAIKI Kazuto; SHIRA Motomaro; KOMATSU Goro; HASEBE Nobuyuki; KAWANO Isao; SHIMIZU Hisayoshi; MIYAMOTO Hideaki; KOBAYASHI Kensei; YOKOBORI Shinichi; MICHIKAMI Tatsuhiro; YAMAMOTO Satoru; YOKOTA Yasuhiro; ARISUMI Hitoshi; ISHIGAMI Genya; FURUTANI Katsushi; KUBOTA Takashi; MICHIKAWA Yuichi; OTSUKI Masatsugu; KATO Hiroki; NISHIBORI Toshihiko; IWATA Takahiro; YAMAMOTO Yukio; ISHIHARA Yoshiaki
    TRANSACTIONS OF THE JAPAN SOCIETY FOR AERONAUTICAL AND SPACE SCIENCES, AEROSPACE TECHNOLOGY JAPAN THE JAPAN SOCIETY FOR AERONAUTICAL AND SPACE SCIENCES 14 (30) Pk_147 - Pk_150 2016 
    <p>We are planning to explore the caverns through the skylight holes on the Moon and Mars. The holes and their associated subsurface caverns are among the most important future exploration targets. The importance of the lunar and Martian holes and their associated caverns is categorized from two aspects: (1) fresh materials are easily observed and sampled there, and (2) the subsurface caverns provide a safe, quiet environment. The expectation of lunar and Martian hole and cavern exploration is increasing in Japan. We name the project as UZUME (Unprecedented Zipangu (Japan) Underworld of the Moon Exploration) whose name is after a Japanese mythology. The ultimate purpose of the UZUME project is to investigate how to expand human activity and survival in space and on extraterrestrial bodies.<i><b> </b></i></p>
  • Tatsuhiro Michikami; Axel Hagermann; Tokiyuki Kadokawa; Akifumi Yoshida; Akira Shimada; Sunao Hasegawa; Akira Tsuchiyama
    ICARUS ACADEMIC PRESS INC ELSEVIER SCIENCE 264 316 - 330 0019-1035 2016/01 [Refereed]
     
    Laboratory impact experiments have found that impact fragments tend to be elongated. Their shapes, as defined by axes a, b and c, these being the maximum dimensions of the fragment in three mutually orthogonal planes (a >= b >= c), are distributed around mean values of the axial ratios b/a similar to 0.7 and c/a similar to 0.5. This corresponds to a:b:c in the simple proportion 2:root 2:1. The shape distributions of some boulders on Asteroid Eros, the small- and fast-rotating asteroids (diameter <200 m and rotation period <1 h), and asteroids in young families, are similar to those of laboratory fragments created in catastrophic disruptions. Catastrophic disruption is, however, a process that is different from impact cratering. In order to systematically investigate the shapes of fragments in the range from impact cratering to catastrophic disruption, impact experiments for basalt targets 5-15 cm in size were performed. A total of 28 impact experiments were carried out by firing a spherical nylon projectile (diameter 7.14 mm) perpendicularly into the target surface at velocities of 1.60-7.13 km/s. More than 12,700 fragments with b a 4 mm generated in the impact experiments were measured. We found that the mean value of c/a in each impact decreases with decreasing impact energy per unit target mass. For instance, the mean value of c/a in an impact cratering event is nearly 0.2, which is considerably smaller than c/a in a catastrophic disruption (similar to 0.5). The data presented here can provide important evidence to interpret the shapes of asteroids and boulders on asteroid surfaces, and can constrain current interpretations of asteroid formation. As an example, by applying our experimental results to the boulder shapes on Asteroid Itokawa's surface, we can infer that Itokawa's parent body must have experienced a catastrophic disruption. (C) 2015 The Authors. Published by Elsevier Inc.
  • Michikami T.; Hasegawa S.; Haruyama J.
    Planetary People The Japanese Society for Planetary Sciences 24 (3) 225 - 232 0918-273X 2015/09 [Refereed]
     
    月や火星には深さ・直径共に数10mから100mにおよぶ縦孔が近年,探査機によって多数観測されるようになった.また縦孔の中には,地下空洞に開いた「天窓」であることが確実なものもある.こうした縦孔は,科学的に多くの興味があるとともに将来的に人類が月や火星に進出したとき,長期滞在に適する基地として有望な場所でもある.月の大きな縦孔については,地下空洞の天井に隕石衝突が引き金となって形成された可能性が示唆されている.本研究では,月に見られる楕円形の大きな縦孔が,隕石の斜め衝突によって形成された可能性を,実験的研究によって明らかにした.
  • T. Michikami; A. Hagermann; H. Miyamoto; S. Miura; J. Haruyama; P. S. Lykawka
    PLANETARY AND SPACE SCIENCE PERGAMON-ELSEVIER SCIENCE LTD 96 71 - 80 0032-0633 2014/06 [Refereed]
     
    High-resolution images reveal that numerous pit craters exist on the surface of Mars. For some pit craters, the depth-to-diameter ratios are much greater than for ordinary craters. Such deep pit craters are generally considered to be the results of material drainage into a subsurface void space, which might be formed by a lava tube, dike injection, extensional fracturing, and dilational normal faulting. Morphological studies indicate that the formation of a pit crater might be triggered by the impact event, and followed by collapse of the ceiling. To test this hypothesis, we carried out laboratory experiments of impact cratering into brittle targets with variable roof thickness. In particular, the effect of the target thickness on the crater formation is studied to understand the penetration process by an impact. For this purpose, we produced mortar targets with roof thickness of 1-6 cm, and a bulk density of 1550 kg/m(3) by using a mixture of cement, water and sand (0.2 mm) in the ratio of 1:1:10, by weight. The compressive strength of the resulting targets is 3.2 +/- 0.9 MPa. A spherical nylon projectile (diameter 7 mm) is shot perpendicularly into the target surface at the nominal velocity of 1.2 km/s, using a two-stage light-gas gun. Craters are formed on the opposite side of the impact even when no target penetration occurs. Penetration of the target is achieved when craters on the opposite sides of the target connect with each other. In this case, the cross section of crater somehow attains a flat hourglass-like shape. We also find that the crater diameter on the opposite side is larger than that on the impact side, and more fragments are ejected from the crater on the opposite side than from the crater on the impact side. This result gives a qualitative explanation for the observation that the Martian deep pit craters lack a raised rim and have the ejecta deposit on their floor instead. (C) 2014 Published by Elsevier Ltd.
  • Akira Tsuchiyama; Masayuki Uesugi; Takashi Matsushima; Tatsuhiro Michikami; Toshihiko Kadono; Tomoki Nakamura; Kentaro Uesugi; Tsukasa Nakano; Scott A Sandford; Ryo Noguchi; Toru Matsumoto; Junya Matsuno; Takashi Nagano; Yuta Imai; Akihisa Takeuchi; Yoshio Suzuki; Toshihiro Ogami; Jun Katagiri; Mitsuru Ebihara; Trevor R Ireland; Fumio Kitajima; Keisuke Nagao; Hiroshi Naraoka; Takaaki Noguchi; Ryuji Okazaki; Hisayoshi Yurimoto; Michael E Zolensky; Toshifumi Mukai; Masanao Abe; Toru Yada; Akio Fujimura; Makoto Yoshikawa; Junichiro Kawaguchi
    Science (New York, N.Y.) 333 (6046) 1125 - 8 2011/08 [Refereed]
     
    Regolith particles on the asteroid Itokawa were recovered by the Hayabusa mission. Their three-dimensional (3D) structure and other properties, revealed by x-ray microtomography, provide information on regolith formation. Modal abundances of minerals, bulk density (3.4 grams per cubic centimeter), and the 3D textures indicate that the particles represent a mixture of equilibrated and less-equilibrated LL chondrite materials. Evidence for melting was not seen on any of the particles. Some particles have rounded edges. Overall, the particles' size and shape are different from those seen in particles from the lunar regolith. These features suggest that meteoroid impacts on the asteroid surface primarily form much of the regolith particle, and that seismic-induced grain motion in the smooth terrain abrades them over time.
  • Tatsuhiro Michikami; Akiko M. Nakamura; Naru Hirata
    ICARUS ACADEMIC PRESS INC ELSEVIER SCIENCE 207 (1) 277 - 284 0019-1035 2010/05 [Refereed]
     
    Laboratory impact experiments have found that the shape of fragments over a broad size range is distributed around the mean value of the axial ratio 2:root 2:1, which is independent of a wide range of experimental conditions. We report the shape statistics of boulders with size of 0.1-30 m on the surface of Asteroid 25143 Itokawa based on high-resolution images obtained by the Hayabusa spacecraft in order to investigate whether their shape distribution is similar to the distribution obtained for fragments (smaller than 0.1 m) in laboratory impact experiments. We also investigated the shapes of boulders with size of 0.1-150 m on Asteroid 433 Eros using a few arbitrary selected images by the NEAR spacecraft, in order to compare those with the shapes on Asteroid ltokawa. In addition, the shapes of small- and fast-rotating asteroids (diameter <200 m and rotation period <1 h), which are natural fragments from past impact events among asteroids, were inferred from archived light curve data taken by ground-based telescopes. The results show that the shape distributions of laboratory fragments are similar to those of the boulders on Eros and of the small- and fast-rotating asteroids, but are different from those on ltokawa. However, we propose that the apparent difference between the boulders of Itokawa and the laboratory fragments is due to the migration of boulders. Therefore, we suggest that the shape distributions of the boulders ranging from 0.1 to 150 m in size and the small- and fast-rotating asteroids are similar to those obtained for the fragments generated in laboratory impact experiments. (C) 2009 Elsevier Inc. All rights reserved.
  • Naru Hirata; Olivier S. Barnouin-Jha; Chikatoshi Honda; Ryosuke Nakamura; Hideaki Miyamoto; Sho Sasaki; Hirohide Demura; Akiko M. Nakamura; Tatsuhiro Michikami; Robert W. Gaskell; Jun Saito
    ICARUS ACADEMIC PRESS INC ELSEVIER SCIENCE 200 (2) 486 - 502 0019-1035 2009/04 [Refereed]
     
    We determined the morphologies and dimensions of possible impact craters on the surface of Asteroid 25143 Itokawa from images taken by the Hayabusa spacecraft. Circular depressions, circular features with flat floors or convex floors, and circular features with smooth surfaces were identified as possible craters. The survey identified 38 candidates with widely varying morphologies including rough, smooth and saddle-shaped floors, a lack of raised rims and fresh material exposures. The average depth/diameter ratio was 0.08 +/- 0.03: these craters are very shallow relative to craters observed on other asteroids. These shallow craters are a result of (1) target curvature influencing the cratering process, (2) raised rim not being generated by this process, and (3) fines infilling the craters. As many of the crater candidates have an unusual appearance, we used a classification scheme that reflects the likelihood of an observed candidate's formation by a hypervelocity impact. We considered a variety of alternative interpretations while developing this scheme, including inherited features from a proto-Itokawa, spall scars created by the disruption of the proto-Itokawa, spall scars following the formation of a large crater on Itokawa itself, and apparent depressions due to random arrangements of boulders. The size-frequency distribution of the crater candidates was close to the empirical saturation line at the largest diameter, and then decline with decreasing diameter. (C) 2009 Elsevier Inc. All rights reserved.
  • Hirata, N; Honda, C; Nakamura, R; Miyamoto, H; Sasaki, S; Demura, H; Nakamura, A. M; Michikami, T; Barnouin-Jha, O.S; Gaskell, R.W; Saito, J
    Icarus 200, 486-502 2009/04 [Refereed]
  • Tatsuhiro Michikami; Akiko M. Nakamura; Naru Hirata; Robert W. Gaskell; Ryosuke Nakamura; Takayuki Honda; Chikatoshi Honda; Kensuke Hiraoka; Jun Saito; Hirohide Demura; Masateru Ishiguro; Hideaki Miyamoto
    EARTH PLANETS AND SPACE TERRA SCIENTIFIC PUBL CO 60 (1) 13 - 20 1343-8832 2008 [Refereed]
     
    The surface of asteroid 25143 Itokawa is covered with numerous boulders although gravity is very small compared with that of other asteroids previously observed from spacecraft. Here we report the size-frequency statistics of boulders on the entire surface of Itokawa based on high-resolution images (1 pixel similar to 0.4 m) obtained by the Hayabusa spacecraft. There are 373 boulders larger than 5 m in mean horizontal dimension on the entire surface-0.393 km(2)-and the number density is nearly 10(3)/km(2). The cumulative boulder size distribution on the entire surface has a power-index of -3.1 +/- 0.1. For the east and west sides and the head and body portions of Itokawa, the power-index of the size distributions and the number densities of boulders of these areas are thought to be similar from the statistical point of view. A global mapping of boulders shows that there is no apparent correlation in the locations of boulders and craters. The ratio of the total volume of the boulders to the total excavated volume of the craters on Itokawa is similar to 25% when only craters larger than 50 m in mean diameter are considered, and this ratio is extremely larger than that on Eros and the Moon, respectively. The origin of boulders on the surface of Itokawa was examined quantitatively by calculating the number of boulders and the size of the largest boulder using a model based on impact cratering experiments. The result indicated that the boulders on the surface of Itokawa cannot solely be the product of craters. Our results suggest that the boulders originated from the disruption of the larger parent body of Itokawa, as has been described in previous papers (Fujiwata et al., Science, 312, 1330-1334, 2006; Saito et al., Science, 312, 1341-1344, 2006).
  • A. M. Nakamura; T. Michikami; N. Hirata; A. Fujiwara; R. Nakamura; M. Ishiguro; H. Miyamoto; H. Demura; K. Hiraoka; T. Honda; C. Honda; J. Saito; T. Hashimoto; T. Kubota
    EARTH PLANETS AND SPACE TERRA SCIENTIFIC PUBL CO 60 (1) 7 - 12 1343-8832 2008 [Refereed]
     
    The subkilometer-size asteroid 25143 Itokawa is considered to have a gravitationally bounded rubble-pile structure. Boulders appearing in high-resolution images retrieved by the Hayabusa mission revealed the genuine outcome of the collisional event involving the asteroid's parent body. Here we report that the boulders' shapes and structures are strikingly similar to laboratory rock impact fragments despite differences of orders of magnitude in scale and complexities of the physical processes. These similarities suggest the universal character of the process throughout the range of these scales, and the brittle and structurally continuous nature regarding the parent body of the boulders. The similarity was likely preserved because of relatively lesser comminuting processes acting on individual boulders; the close assemblages of similar appearing boulders (a boulder family) represent the impact destruction of boulders on the surface.
  • Hideaki Miyamoto; Hajime Yano; Daniel J. Scheeres; Shinsuke Abe; Olivier Barnouin-Jha; Andrew F. Cheng; Hirohide Demura; Robert W. Gaskell; Naru Hirata; Masateru Ishiguro; Tatsuhiro Michikami; Akiko M. Nakamura; Ryosuke Nakamura; Jun Saito; Sho Sasaki
    SCIENCE AMER ASSOC ADVANCEMENT SCIENCE 316 (5827) 1011 - 1014 0036-8075 2007/05 [Refereed]
     
    High-resolution images of the surface of asteroid Itokawa from the Hayabusa mission reveal it to be covered with unconsolidated millimeter-sized and larger gravels. Locations and morphologic characteristics of this gravel indicate that Itokawa has experienced considerable vibrations, which have triggered global-scale granular processes in its dry, vacuum, microgravity environment. These processes likely include granular convection, landslide-like granular migrations, and particle sorting, resulting in the segregation of the fine gravels into areas of potential lows. Granular processes become major resurfacing processes because of Itokawa's small size, implying that they can occur on other small asteroids should those have regolith.
  • Tatsuhiro Michikami; Kouichi Moriguchi; Sunao Hasegawa; Akira Fujiwara
    PLANETARY AND SPACE SCIENCE PERGAMON-ELSEVIER SCIENCE LTD 55 (1-2) 70 - 88 0032-0633 2007/01 [Refereed]
     
    Impact cratering experiments on porous targets with various compressive strength ranging from similar to 0.5 to similar to 250 MPa were carried out in order to investigate the relationship between the ejecta velocity, and material strength or porosity of the target. A spherical alumina projectile (diameter similar to 1 mm) was shot perpendicularly into the target surface with velocity ranging from 1.2 to 4.5 km/s (nominal 4 km/s), using a two-stage light-gas gun. The ejecta velocity was estimated from the fall point distance of ejecta. The results show that there are in fact a large fraction of ejecta with very low velocities when the material strength of the target is small and the porosity is high. As an example, in the case of one specific target (compressive strength similar to 0.5 MPa and porosity 43%), the amount of ejecta with velocities lower than 1 m/s is about 40% of the total mass. The average velocity of the ejecta decreases with decreasing material strength or increasing the porosity of the target. Moreover, in our experiments, the ejecta velocity distributions normalized to total ejecta, mass seem to be mainly dependent on the material strength of the target, and not so greatly on the porosity. We also compare our experimental results with those of Gault et al. [1963. Spray ejected from the lunar surface by meteoroid impact. NASA Technical Note D-1767] and Housen [1992. Crater ejecta velocities for impacts on rocky bodies. LPSC XXIII, 555-556] for the ejecta velocity distribution using Housen's nondimensional scaling parameter. The ejecta velocity distributions of our experiments are lower than those of Gault et al. [1963. Spray ejected from the lunar surface by meteoroid impact. NASA Technical Note D-1767] and Housen [1992. Crater ejecta velocities for impacts on rocky bodies. LPSC XIII, 555-556]. (c) 2006 Elsevier Ltd. All rights reserved.
  • J Saito; H Miyamoto; R Nakamura; M Ishiguro; T Michikami; AM Nakamura; H Demura; S Sasaki; N Hirata; C Honda; A Yamamoto; Y Yokota; T Fuse; F Yoshida; DJ Tholen; RW Gaskell; T Hashimoto; T Kubota; Y Higuchi; T Nakamura; P Smith; K Hiraoka; T Honda; S Kobayashi; M Furuya; N Matsumoto; E Nemoto; A Yukishita; K Kitazato; B Dermawan; A Sogame; J Terazono; C Shinohara; H Akiyama
    SCIENCE AMER ASSOC ADVANCEMENT SCIENCE 312 (5778) 1341 - 1344 0036-8075 2006/06 [Refereed]
     
    Rendezvous of the Japanese spacecraft Hayabusa with the near-Earth asteroid 25143 Itokawa took place during the interval September through November 2005. The onboard camera imaged the solid surface of this tiny asteroid ( 535 meters by 294 meters by 209 meters) with a spatial resolution of 70 centimeters per pixel, revealing diverse surface morphologies. Unlike previously explored asteroids, the surface of Itokawa reveals both rough and smooth terrains. Craters generally show unclear morphologies. Numerous boulders on Itokawa's surface suggest a rubble-pile structure.
  • 福島高専物理教育におけるビデオオンデマンドを利用したeランニング教材の開発
    布施雅彦; 鈴木三男; 根本信行; 道上達広; 小澤哲
    高専教育 29 439 - 444 2006/03 [Refereed]
  • Y Hirase; AM Nakamura; T Michikami
    PLANETARY AND SPACE SCIENCE PERGAMON-ELSEVIER SCIENCE LTD 52 (12) 1103 - 1108 0032-0633 2004/10 [Refereed]
     
    The relation between the size and velocity of impact crater ejecta has been studied by both laboratory experiments and numerical modeling. An alternative method, used here, is to analyze the record of past impact events, such as the distribution of secondary craters on planetary surfaces, as described by Vickery (Icarus 67 (1986) 224; Geophys. Res. Lett. 14 (1987) 726). We first applied the method to lunar images taken by the CLEMENTINE mission, which revealed that the size-velocity relations of ejecta from craters 32 and 40 km in diameter were similar to those derived by Vickery for a crater 39 km in diameter. Next, we studied the distribution of small craters in the vicinity of kilometer-sized craters on three images from the Mars Orbiter Camera (MOC) on board the Mars Global Surveyor (MGS). If these small craters are assumed to be secondaries ejected from the kilometer-sized crater in each image, the ejection velocities are of hundreds of meters per second. These data fill a gap between the previous results of Vickery and those of laboratory studies. (C) 2004 Elsevier Ltd. All rights reserved.
  • 小惑星25143イトカワのレゴリス厚さと岩塊（ブロック）の数密度の推定
    道上達広
    日本惑星科学会誌 遊星人 13 (2) 71 - 79 2004 [Refereed]
  • T. Takano; M. Yoshikawa; Y. Ishibashi; T. Michikami; J. Watanabe; T. Nakamura; T. Tajima; M. Toda; B. Suzuki
    Science and Technology Series 100 75 - 84 0278-4017 2001 
    Leonids meteoroids raised attention in space organizations in the world due to probable collision hazards to artificial satellites. This paper describes the plan of the Leonids measurement campaign in Japan and the results. The correlation between optical and radiowave observations was especially focused on. The countermeasures to lessen the Leonids hazards to satellites will also be presented.
  • 小惑星レゴリス衝突進化
    道上達広; 山本聡; 長沢真樹子; 中澤暁
    日本惑星科学会誌 遊星人 9 (4) 186 - 196 2000 [Refereed]

Books etc

MISC

  • Kikuchi Shota; Watanabe Sei-ichiro; Watanabe Sei-ichiro; Saiki Takanao; Yabuta Hikaru; Sugita Seiji; Sugita Seiji; Sugita Seiji; Morota Tomokatsu; Morota Tomokatsu; Hirata Naru; Hirata Naoyuki; Michikami Tatsuhiro; Honda Chikatoshi; Yokota Yashuhiro; Honda Rie; Sakatani Naoya; Sakatani Naoya; Okada Tatsuaki; Shimaki Yuri; Matsumoto Koji; Noguchi Rina; Takei Yuto; Terui Fuyuto; Ogawa Naoko; Yoshikawa Kent; Ono Go; Mimasu Yuya; Sawada Hirotaka; Ikeda Hitoshi; Hirose Chikako; Takahashi Tadateru; Takahashi Tadateru; Fujii Atsushi; Yamaguchi Tomohiro; Yamaguchi Tomohiro; Ishihara Yoshiaki; Ishihara Yoshiaki; Nakamura Tomoki; Kitazato Kohei; Wada Koji; Tachibana Shogo; Tachibana Shogo; Tatsumi Eri; Tatsumi Eri; Matsuoka Moe; Senshu Hiroki; Kameda Shingo; Kouyama Toru; Yamada Manabu; Shirai Kei; Shirai Kei; Cho Yuichiro; Ogawa Kazunori; Ogawa Kazunori; Yamamoto Yukio; Miura Akira; Iwata Takahiro; Namiki Noriyuki; Hayakawa Masahiko; Abe Masanao; Tanaka Satoshi; Yoshikawa Makoto; Nakazawa Satoru; Tsuda Yuichi  Space Science Reviews  216-  (7)  2020
  • TSUCHIYAMA Akira; MATSUSHIMA Takashi; NAKANO Tsukasa; MICHIKAMI Tatsuhiro; UESUGI Kentaro; TAKEUCHI Akihisa; SUZUKI Yoshio; MATSUMOTO Toru; MATSUNO Junya; SHIMADA Akira; MATSUNO Junya; KADONO Toshihiko  日本鉱物科学会年会講演要旨集  2013-  156  -156  2013/09
  • Tsuchiyama Akira; Noguchi Ryo; Matsumoto Toru; Matsuno Junya; Nagano Takashi; Imai Yuta; Takeuchi Akihisa; Suzuki Yoshio; Ogami Toshihiro; Katagiri Jun; Ebihara Mitsuru; Uesugi Masayuki; Ireland Trevor; Kitajima Fumio; Nagao Keisuke; Naraoka Hiroshi; Noguchi Takaaki; Okazaki Ryuji; Yurimoto Hisayoshi; Zolensky Michael; Mukai Toshifumi; Abe Masanao; Matsushima Takashi; Yada Toru; Fujimura Akio; Yoshikawa Makoto; Kawaguchi Jun'ichiro; Michikami Tatsuhiro; Kadono Toshihiko; Nakamura Tomoki; Uesugi Kentaro; Nakano Tsukasa; Sandford Scott  Annual Meeting of the Geological Society of Japan  2011-  (0)  1  -1  2011
  • Tsuchiyama Akira; Noguchi Ryo; Matsumoto Toru; Matsuno Junya; Nagano Takashi; Imai Yuta; Takeuchi Akihisa; Yoshio Suzuki; Ogami Toshihiro; Katagiri Jun; Ebihar Mitsuru; Uesugi Masayuki; Ireland Trevor; Kitajima Fumio; Nagao Keisuke; Naraoka Hiroshi; Noguchi Takaaki; Okazaki Ryuji; Yurimoto Hisayoshi; Zolensky Michael; Hayabusa Curation Team; Matsushima Takashi; Michikami Tatsuhiro; kadono Toshihiko; Nakamura Tomoki; Uesugi Kentaro; Nakano Tsukasa; Sandford Scott A  Abstracts of Annual Meeting of the Geochemical Society of Japan  58-  (0)  169  -169  2011
  • Michikami Tatsuhiro; Nakamura Akiko; Hirata Naru  Abstracts for fall meeting of the Japanese Society for Planetary Science  2007-  (0)  79  -79  2007
  • Hirata Naru; Demura Hirohide; Nakamura Ryosuke; Abe Shinsuke; Nakamura Akiko; Michikami Tatsuhiro; Noguchi Takaaki; Sasaki Akira  Abstracts for fall meeting of the Japanese Society for Planetary Science  2007-  (0)  78  -78  2007
  • Hirata Naru; Nakamura Ryosuke; Honda Chikatoshi; Nakamura Akiko; Demura Hirohide; Michikami Tatsuhiro; Miyamoto Hideaki; Saito Jun  Abstracts for fall meeting of the Japanese Society for Planetary Science  2006-  (0)  73  -73  2006

Awards & Honors

  • 2010/12 小惑星探査機「はやぶさ」功労者感謝状 宇宙開発担当大臣
  • 2010/12 小惑星探査機「はやぶさ」功労者感謝状 文部科学大臣
  • 国際天文学連合から 小惑星 23169 Michikami 命名

Research Grants & Projects

  • 日本学術振興会：科学研究費助成事業
    Date (from‐to) : 2020/04 -2023/03 
    Author : 道上 達広
     
    最近の研究で、小惑星リュウグウに含水鉱物の形で水が存在することが発見された。近年、地球の水は小惑星リュウグウのような炭素質小惑星から供給された可能性が大きいと考えられている。その供給形態の１つとして、小惑星表層のレゴリス層と呼ばれる細粒の粒子が、宇宙空間に放出され、惑星間塵として地球にもたらされることが挙げられる。しかしながら、小惑星リュウグウのような微小重力下で、どのようにレゴリス層が形成されたかよく分かっていない。 レゴリス層の主要な形成要因として、小惑星の昼夜の温度差がもたらす熱疲労による表面物質の細粒化、隕石衝突による破片の再集積の２つが考えられる。表面物質が細粒化された場合、太陽風や微小隕石による宇宙風化作用で、小惑星表面のスペクトルが変化する。また、隕石衝突によるクレーター形成やそれに伴う表層のガーデニングなど、小惑星表面は当初あった状態から変化する。 本研究では、レゴリス層は隕石衝突によって形成されたとの立場で、炭素質小惑星と同じ炭素質隕石に対して衝突実験を行い、衝突破片を調べることにした。具体的には、衝突前後の炭素質隕石の内部構造をX線CT撮像することで、クラックの空間分布、特にコンドリュール中のクラックの進展を調べた。学術的な問いは、「炭素質小惑星のレゴリス層形成は、衝突破片の再集積か？」である。 2020年度は、CV隕石であるアエンデ隕石に対して、2021年度は、CM隕石であるマーチソン隕石、アグアス・ザルカス隕石に対して実験を行った。その結果、コンドリュール中のクラック進展はCV隕石とCM隕石で異なることが分かった。これはCM隕石が水質変成作用を受けていることが原因であることが本研究によって初めて分かった。2023年度に小惑星ベンヌ（CM隕石と同じ物質）からサンプル粒子が地球に持ち帰られることから、比較研究で地球の水の起源に迫ることが期待される。
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research
    Date (from‐to) : 2010 -2011 
    Author : MICHIKAMI Tatsuhiro
     
    The surface of asteroid 25143 Itokawa is covered with numerous boulders although gravity is very small compared with that of other asteroids previously observed from spacecraft. The bulk porosiy of Itokawa is～ 40%, which is larger than that of asteroid Eros. Impact experiments on porous targets were carried out, in order to investigate the relationship between the ejecta velocity and the porosity of the target on catastrophic disruption. The result shows that antipodal velocity is mainly dependent on the shock pressure attenuation of the target, and not so greatly on the porosity.
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research
    Date (from‐to) : 2006 -2008 
    Author : MIURA Seiichiro; WATANABE Hiroshi; KASUGA Takeshi; IKAWA Osamu; MICHIKAMI Tatsuhiro; FUSE Masahiko
     
    青少年の科学技術への興味関心を高めるために,ものづくりの要素を取り入れた初心者向け工学教育教材の開発を行った.教材は,科学技術の各分野を横断的に取り扱えるモデルロケットを通して組み立て,学習教材付きモデルロケット設計支援ソフト,論理回路の基礎を含んだ発射台・発射装置の作り方,積載用電気電子装置の作り方などを作成した.公開講座の実習状況や調査結果等より,初心者用教材としての一定の効果を確認した.
  • Formation and Evolution of Asteroid
    The Other Research Programs
    Date (from‐to) : 1998 -2008
  • 小惑星（惑星）の起源、進化に関する研究
    共同研究

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