Formation and topographic relaxation of spinning top-shaped asteroids

• Project/Area Number: 19H01951
• Research Category: Grant-in-Aid for Scientific Research (B)
• Allocation Type: Single-year Grants
• Section: 一般
• Review Section: Basic Section 17010:Space and planetary sciences-related
• Research Institution: Nagoya University
• Principal Investigator: Watanabe Sei-ichiro 名古屋大学, 環境学研究科, 教授 (50230967)
• Co-Investigator(Kenkyū-buntansha): 桂木 洋光 大阪大学, 大学院理学研究科, 教授 (30346853) ; 諸田 智克 東京大学, 大学院理学系研究科(理学部), 准教授 (30415898)
• Project Period (FY): 2019-04-01 – 2022-03-31
• Project Status: Completed (Fiscal Year 2022)
• Budget Amount: ¥10,790,000 (Direct Cost: ¥8,300,000、Indirect Cost: ¥2,490,000); Fiscal Year 2021: ¥2,730,000 (Direct Cost: ¥2,100,000、Indirect Cost: ¥630,000); Fiscal Year 2020: ¥3,120,000 (Direct Cost: ¥2,400,000、Indirect Cost: ¥720,000); Fiscal Year 2019: ¥4,940,000 (Direct Cost: ¥3,800,000、Indirect Cost: ¥1,140,000)
• Keywords: 小惑星 / 微惑星 / 粉体 / 回転変形 / 惑星探査 / 高速回転装置 / 遠心力 / コマ型形状 / 小惑星探査 / 小惑星リュウグウ / ラブルパイル天体 / 高速自転天体 / 太陽系形成論 / 高速度回転装置

Outline of Research at the Start

惑星の材料となった微惑星の力学的性質を知るには、小惑星探査の情報が非常に重要で
ある。特徴的なコマ型形状をした小惑星リュウグウおよびBennuのはやぶさ2およびOSIRIS-RExによる表面画像から、形状・地形の形成・進化過程と岩塊（boulders）の分布・移動を可能な限り読み出す。かつての天体の高速自転によって、このコマ型形状と岩塊の一様かつ高密度な分布が作られるかを室内粉体実験と計算機シミュレーションから明らかにする。また、自転周期が長くなった後のコマ型形状の天体衝突による変化過程が、衝撃波の減衰率への依存性も調べる。これらの結果から微小重力天体の形状形成とその後の変化を明らかにする。

Outline of Final Research Achievements

In small celestial bodies with gravity, we have clarified that a spinning top-shaped form can be produced by landslides during high-speed rotation if an effective frictional force operates due to the cohesion of several Pa or more between constituent particles. It was shown from our laboratory experiments and analysis of the size dependence of flow rock masses on Ryugu that landslides are limited to the surface layer. Additionally, it was experimentally demonstrated that the final shape can be accurately described by the balance among gravity, centrifugal force, and friction. Moreover, we revealed the existence of relaxation of small craters and surface flow due to vibrations induced by meteorite collision. We estimate that Ryugu, after becoming a top-shaped form due to landslides during high-speed rotation about 10 million years ago, spun down due to the YORP effect, and in recent years, surface flow excited by vibrations has been occurring from the equator to the polar direction.

Academic Significance and Societal Importance of the Research Achievements

本研究成果の学術的意義は次の点である。(1)高速自転小天体の物理を明らかにするための実験的手法を確立したこと、(2)数値シミュレーション、室内実験、探査データ解析を総合して、太陽系小天体の1つの典型的な形状であるコマ型形状の成因について、蓋然性の高いモデルを提唱したこと、(3)重力・遠心力・摩擦力のつりあいという単純なモデルで瓦礫集積天体の形状が表現できることを明らかにしたこと。
本研究の社会的意義は、国民の高い関心を集めたはやぶさ2による小惑星リュウグウ探査に基づいて、天体形状や岩塊分布といった視覚的にも把握しやすい謎を提示して、高校生でも理解できる説明が可能な結果を得た点にある。

Research Products

• [Int'l Joint Research] DLR(ドイツ)
• [Int'l Joint Research] CNES(フランス)
• [Int'l Joint Research] Univesity of Arizona(米国)
• [Journal Article] Formation and evolution of carbonaceous asteroid Ryugu: Direct evidence from returned samples (2023)
  • Author(s): Nakamura T.、Matsumoto M.、Amano K.、Enokido Y.、Zolensky M. E.、Mikouchi T.、Genda H.、Tanaka S.、Zolotov M. Y.、Kurosawa K. .. Yabuta H. ... et al.
  • Journal Title: Science Volume: 379 Issue: 6634 Pages: 8671-8671
  • DOI: 10.1126/science.abn8671
  • Peer Reviewed / Open Access / Int'l Joint Research
• [Journal Article] History-dependent growth and reduction of the ripples formed on a swept granular track (2022)
  • Author(s): Hata Shunto、Katsura Makoto、Katsuragi Hiroaki
  • Journal Title: The European Physical Journal E Volume: 45 Issue: 1 Pages: 8-8
  • DOI: 10.1140/epje/s10189-022-00165-7
  • Peer Reviewed
• [Journal Article] History-dependent deformation of a rotated granular pile governed by granular friction (2022)
  • Author(s): Irie Terunori、Yamaguchi Ryusei、Watanabe Sei-ichiro、Katsuragi Hiroaki
  • Journal Title: Advanced Powder Technology Volume: 33 Issue: 8 Pages: 103629-103629
  • DOI: 10.1016/j.apt.2022.103629
  • Peer Reviewed
• [Journal Article] Resurfacing processes constrained by crater distribution on Ryugu (2022)
  • Author(s): Takaki Naofumi、Cho Yuichiro、Morota Tomokatsu、Tatsumi Eri、Honda Rie、Kameda Shingo、Yokota Yasuhiro、Sakatani Naoya、Kouyama Toru、Hayakawa Masahiko、Matsuoka Moe、Yamada Manabu、Honda Chikatoshi、Suzuki Hidehiko、Yoshioka Kazuo、Ogawa Kazunori、Sawada Hirotaka、Michel Patrick、Sugita Seiji
  • Journal Title: Icarus Volume: 377 Pages: 114911-114911
  • DOI: 10.1016/j.icarus.2022.114911
  • Peer Reviewed / Int'l Joint Research
• [Journal Article] Particle size distributions inside and around the artificial crater produced by the Hayabusa2 impact experiment on Ryugu (2022)
  • Author(s): Ogawa K.、Sakatani N.、Kadono T.、Arakawa M.、Honda R.、Wada K.、et al.
  • Journal Title: Earth, Planets and Space Volume: 74 Issue: 1 Pages: 153-153
  • DOI: 10.1186/s40623-022-01713-3
  • Peer Reviewed / Open Access / Int'l Joint Research
• [Journal Article] Pebbles and sand on asteroid (162173) Ryugu: In situ observation and particles returned to Earth (2022)
  • Author(s): Tachibana S.、Abe M. et al.
  • Journal Title: Science Volume: 375 Issue: 6584 Pages: 1011-1016
  • DOI: 10.1126/science.abj8624
  • Peer Reviewed / Open Access / Int'l Joint Research
• [Journal Article] Measurement of surface deformation and cohesion of a granular pile under the effect of centrifugal force (2021)
  • Author(s): Irie Terunori、Yamaguchi Ryusei、Watanabe Sei-ichiro、Katsuragi Hiroaki
  • Journal Title: Measurement Science and Technology Volume: 32 Issue: 12 Pages: 125301-125301
  • DOI: 10.1088/1361-6501/ac1b25
  • Peer Reviewed
• [Journal Article] Deformation of a rotated granular pile governed by body-force-dependent friction (2021)
  • Author(s): Irie Terunori、Yamaguchi Ryusei、Watanabe Sei-ichiro、Katsuragi Hiroaki
  • Journal Title: Physical Review E Volume: 104 Issue: 6 Pages: 064902-064902
  • DOI: 10.1103/physreve.104.064902
  • Peer Reviewed
• [Journal Article] Geologic History and Crater Morphology of Asteroid (162173) Ryugu (2021)
  • Author(s): Cho Y.、Morota T.、Kanamaru M.、Takaki N.、Yumoto K.、Ernst C. M.、et al.
  • Journal Title: Journal of Geophysical Research: Planets Volume: 126 Issue: 8
  • DOI: 10.1029/2020je006572
  • Peer Reviewed / Open Access / Int'l Joint Research
• [Journal Article] SPH simulations for shape deformation of rubble-pile asteroids through spinup: The challenge for making top-shaped asteroids Ryugu and Bennu (2021)
  • Author(s): Sugiura Keisuke、Kobayashi Hiroshi、Watanabe Sei-ichiro、Genda Hidenori、Hyodo Ryuki、Inutsuka Shu-ichiro
  • Journal Title: Icarus Volume: 365 Pages: 114505-114505
  • DOI: 10.1016/j.icarus.2021.114505
  • Peer Reviewed / Open Access
• [Journal Article] YORP Effect on Asteroid 162173 Ryugu: Implications for the Dynamical History (2021)
  • Author(s): Kanamaru Masanori、Sasaki Sho、Morota Tomokatsu、Cho Yuichiro、Tatsumi Eri、Hirabayashi Masatoshi、Hirata Naru、Senshu Hiroki、Shimaki Yuri、Sakatani Naoya、Tanaka Satoshi、Okada Tatsuaki、Usui Tomohiro、Sugita Seiji、Watanabe Sei‐ichiro
  • Journal Title: Journal of Geophysical Research: Planets Volume: 126 Issue: 12
  • DOI: 10.1029/2021je006863
  • Peer Reviewed / Open Access / Int'l Joint Research
• [Journal Article] Collisional history of Ryugu’s parent body from bright surface boulders (2021)
  • Author(s): Tatsumi E.、Sugimoto C.、Riu L.、... Yabuta, H. ... et al. (75人中67番目)
  • Journal Title: Nature Astronomy Volume: 5 Issue: 1 Pages: 39-45
  • DOI: 10.1038/s41550-020-1179-z
  • Peer Reviewed / Int'l Joint Research
• [Journal Article] Crater depth-to-diameter ratios on asteroid 162173 Ryugu (2021)
  • Author(s): Noguchi Rina、Hirata Naoyuki、Hirata Naru、Shimaki Yuri、Nishikawa Naoki、Tanaka Sayuri、Sugiyama Takaaki、Morota Tomokatsu、Sugita Seiji、Cho Yuichiro、Honda Rie、Kameda Shingo他
  • Journal Title: Icarus Volume: 354 Pages: 114016-114016
  • DOI: 10.1016/j.icarus.2020.114016
  • Peer Reviewed / Int'l Joint Research
• [Journal Article] Thermally altered subsurface material of asteroid (162173) Ryugu (2021)
  • Author(s): Kitazato K.、Milliken R. E.、Iwata T. .. Yabuta, H. ... et al. (101人中76番目)
  • Journal Title: Nature Astronomy Volume: 5 Issue: 3 Pages: 246-250
  • DOI: 10.1038/s41550-020-01271-2
  • Peer Reviewed / Int'l Joint Research
• [Journal Article] Sample collection from asteroid (162173) Ryugu by Hayabusa2: Implications for surface evolution (2020)
  • Author(s): Morota, T., Sugita, S., Cho, Y., Kanamaru, M., Tatsumi, E., Sakatani, N., Honda, R., Hirata, N. et al.
  • Journal Title: Science Volume: 368 Issue: 6491 Pages: 654-659
  • DOI: 10.1126/science.aaz6306
  • Peer Reviewed / Open Access / Int'l Joint Research
• [Journal Article] Spin-driven evolution of asteroids' top-shapes at fast and slow spins seen from (101955) Bennu and (162173) Ryugu (2020)
  • Author(s): Hirabayashi Masatoshi、Nakano Ryota、Tatsumi Eri、Walsh Kevin J.、Barnouin Olivier S.、Michel Patrick、Hartzell Christine M.、Britt Daniel T.、Sugita Seiji、Watanabe Sei-ichiro、Bottke William F.、Scheeres Daniel J.、Ballouz Ronald-Louis、Cho Yuichiro、Morota Tomokatsu、Howell Ellen S.、Lauretta Dante S.
  • Journal Title: Icarus Volume: 352 Pages: 113946-113946
  • DOI: 10.1016/j.icarus.2020.113946
  • Peer Reviewed / Int'l Joint Research
• [Journal Article] Hayabusa2 Landing Site Selection: Surface Topography of Ryugu and Touchdown Safety (2020)
  • Author(s): Kikuchi Shota、Watanabe Sei-ichiro、Saiki Takanao、Yabuta Hikaru et al. (53人中4番目)
  • Journal Title: Space Science Reviews Volume: 216 Issue: 7 Pages: 116-116
  • DOI: 10.1007/s11214-020-00737-z
  • Peer Reviewed / Open Access / Int'l Joint Research
• [Journal Article] The spatial distribution of impact craters on Ryugu (2020)
  • Author(s): Hirata Naoyuki、Morota Tomokatsu、Cho Yuichiro、Kanamaru Masanori、Watanabe Sei-ichiro、Sugita Seiji、Hirata Naru、Yamamoto Yukio、Noguchi Rina、Shimaki Yuri、Tatsumi Eri、Yoshioka Kazuo、Sawada Hirotaka、Yokota Yasuhiro、Sakatani Naoya、Hayakawa Masahiko、Matsuoka Moe、Honda Rie、Kameda Shingo
  • Journal Title: Icarus Volume: 338 Pages: 113527-113527
  • DOI: 10.1016/j.icarus.2019.113527
  • NAID: 120006766134
  • Peer Reviewed / Int'l Joint Research
• [Journal Article] Highly porous nature of a primitive asteroid revealed by thermal imaging (2020)
  • Author(s): T.Okada, T.Fukuhara, S.Tanaka, M.Taguchi, T.Arai, H.Senshu, N.Sakatani, Y.Shimaki, H.Demura, Y.Ogawa, K.Suko, T.Sekiguchi, T.Kouyama, J.Takita, T.Matsunaga, T.Imamura, T.Wada, S.Hasegawa, J.Helbert, T.G.Muller, A.Hagermann, J.Biele, M.Grott, M.Hamm, M.Delbo, N.Hirata, N.Hirata, Y.Yamamoto, A.Miura, et al.
  • Journal Title: Nature Volume: 579 Issue: 7800 Pages: 518-522
  • DOI: 10.1038/s41586-020-2102-6
  • Peer Reviewed / Int'l Joint Research
• [Journal Article] Hayabusa2 arrives at the carbonaceous asteroid 162173 Ryugu?A spinning top?shaped rubble pile (2019)
  • Author(s): Watanabe S.、Hirabayashi M.、Hirata N. et al.
  • Journal Title: Science Volume: 364 Issue: 6437 Pages: 268-272
  • DOI: 10.1126/science.aav8032
  • Peer Reviewed / Open Access / Int'l Joint Research
• [Journal Article] The geomorphology, color, and thermal properties of Ryugu: Implications for parent-body processes (2019)
  • Author(s): Seiji Sugita, R. Honda, T. Morota, S. Kameda, H. Sawada, E. Tatsumi, M. Yamada, C. Honda, Y. Yokota, T. Kouyama, N. Sakatani, K. Ogawa, H. Suzuki, T. Okada, N. Namiki, S. Tanaka, Y. Iijima, K. Yoshioka, M. Hayakawa, Y. Cho, M. Matsuoka, N. Hirata, N. Hirata, H. Miyamoto, Jun Kimura
  • Journal Title: Science Volume: 17 Issue: 6437 Pages: 252-252
  • DOI: 10.1126/science.aaw0422
  • Peer Reviewed / Open Access / Int'l Joint Research
• [Journal Article] Images from the surface of asteroid Ryugu show rocks similar to carbonaceous chondrite meteorites (2019)
  • Author(s): Jaumann R., Schmitz N., Ho T.-M., Schrider S. E., Otto K. A., Stephan K., Elgner S., Krohn K., Preusker F., Scholten F., Biele J., Ulamec S., Krause C., Sugita S., Matz K.-D., Roatsch T., Parekh R., Mottola S., Grott M., Michel P., ..., Yabuta H., ... et al.
  • Journal Title: Science Volume: 365 Issue: 6455 Pages: 817-820
  • DOI: 10.1126/science.aaw8627
  • Peer Reviewed / Open Access / Int'l Joint Research
• [Journal Article] Boulder size and shape distributions on asteroid Ryugu (2019)
  • Author(s): Michikami Tatsuhiro、Honda Chikatoshi、Miyamoto Hideaki、Hirabayashi Masatoshi、Hagermann Axel、Irie Terunori、Nomura Keita、Ernst Carolyn M.、et al.
  • Journal Title: Icarus Volume: 331 Pages: 179-191
  • DOI: 10.1016/j.icarus.2019.05.019
  • Peer Reviewed / Int'l Joint Research
• [Presentation] Construction of the local digital elevation models of the asteroid Ryugu by structure-from-motion method (2023)
  • Author(s): Y. Aikyo, T. Morota, S. Sugita, Y. Cho, N. Hirata, T. Michikami, R. Honda, E. Tatsumi, N. Sakatani, S. Kameda, M. Yamada, Y. Yokota, M. Matsuoka, C. Honda, T. Kouyama, H. Suzuki, M. Hayakawa, K. Yoshioka, K. Ogawa
  • Organizer: 54th Lunar and Planetary Science Conference
  • Int'l Joint Research
• [Presentation] Formation and evolution of planetesimals revealed from the Hayabusa2 mission (2023)
  • Author(s): Sei-ichiro Watanabe
  • Organizer: 82nd Fujihara Seminar
  • Int'l Joint Research / Invited
• [Presentation] 粉体ヒープの回転による付着力評価 (2022)
  • Author(s): 入江輝紀，山口隆正，渡邊誠一郎，桂木洋光
  • Organizer: 日本物理学会 第77回年次大会
• [Presentation] 2次元回転砂山の変形と摩擦角の体積力依存性 (2022)
  • Author(s): 桂木洋光, 入江輝紀, 渡邊誠一郎, 山口隆正
  • Organizer: 日本物理学会 2022年秋季大会
• [Presentation] はやぶさ2 ONC画像から構築したリュウグウ表面ローカル三次元地形モデルの精度評価と微小地形の計測 (2022)
  • Author(s): 愛敬雄太，諸田智克，杉田精司，長勇一郎，平田成，本田理恵，巽瑛理，坂谷尚哉，亀田真吾，山田学，横田康弘，松岡萌，本田親寿，神山徹，鈴木秀彦，早川雅彦，吉岡和夫，小川和律，澤田弘崇
  • Organizer: 日本惑星科学会2022年秋季講演会
• [Presentation] 自転変化に伴うリュウグウの表層進化 (2022)
  • Author(s): 渡邊誠一郎，山田理央奈，諸田智克
  • Organizer: 日本惑星科学会2022年秋季講演会
• [Presentation] Scientific discoveries of the Hayabusa2 mission, sample return from asteroid Ryugu (2022)
  • Author(s): Sei-ichiro Watanabe
  • Organizer: 31th General Assembly, Inrernational Astronomical Union
  • Int'l Joint Research / Invited
• [Presentation] Surface age of Ryugu's boulders based on small crater statistics (2021)
  • Author(s): Y. Takai, T. Morota
  • Organizer: Japan Geoscience Union Meeting 2021
  • Int'l Joint Research
• [Presentation] Orientaions of boulders and relationship with gravitational slope on asteroid Ryugu: implications for surface evolution (2021)
  • Author(s): T. Ebihara, T. Morota
  • Organizer: Japan Geoscience Union Meeting 2021
  • Int'l Joint Research
• [Presentation] Impact Strength of Ryugu's Boulder Inferred from Meter-Sized Crater Statistics (2021)
  • Author(s): T. Morota、S. Sugita、Y. Cho、E. Tatsumi、N. Sakatani、R. Honda、S. Kameda、M. Yamada、Y. Yokota、C. Honda、t. Kouyama、M. Matsuoka、M. Hayakawa、H. Sawada、K. Ogawa、H. Suzuki、K. Yoshioka、M. Kanamaru、M. Hirabayashi、T. Michikawa
  • Organizer: Lunar and Planetary Science Conference 2021
  • Int'l Joint Research
• [Presentation] Statistics of Small Craters Observed on Boulder Surface of Asteroid Ryugu (2021)
  • Author(s): Y. Takai, T. Morota、K. Yumoto、R. Honda、S. Kameda、E. Tatsumi、Y. Cho、K. Yoshioka、H. Sawada、Y. Yokota、N. Sakatani、M. Hayakawa、M. Matsuoka、M. Yamada、T. Kouyama、H. Suzuki、C. Honda、K. Ogawa、S. Sugita
  • Organizer: Lunar and Planetary Science Conference 2021
  • Int'l Joint Research
• [Presentation] 遠心力による砂山の形状変化および流動特性 (2020)
  • Author(s): 入江輝紀, 山口隆正, 渡邊誠一郎, 桂木洋光
  • Organizer: 日本惑星科学会 2020年秋季講演会
• [Presentation] 回転実験による砂山形状変化のヒステリシスと自転コマ型小惑星の形状安定性 (2020)
  • Author(s): 入江輝紀, 山口隆正, 渡邊誠一郎, 桂木洋光
  • Organizer: 混相流シンポジウム2020
• [Presentation] はやぶさ２のタッチダウンによって明らかとなった小惑星リュウグウの表層の進化 (2020)
  • Author(s): 諸田智克ほか
  • Organizer: JpGU-AGU Joint Meeting 2020
  • Int'l Joint Research
• [Presentation] Paucity of boulders in shallow craters on asteroid 162173 Ryugu (2020)
  • Author(s): Sei-ichiro Watanabe et al.
  • Organizer: 51th Lunar and Planetary Science Conference
  • Int'l Joint Research
• [Presentation] Color and albedo changes of Ryugu's surface observed in the touchdown operation of Hayabusa2 (2020)
  • Author(s): Tomokatsu Morota et al.
  • Organizer: 51th Lunar and Planetary Science Conference
  • Int'l Joint Research
• [Presentation] The shape and origin of the rubble-pile asteroid Ryugu (2019)
  • Author(s): Sei-ichiro Watanabe et al.
  • Organizer: Japan Geoscience Union Meeting 2019
  • Int'l Joint Research / Invited
• [Presentation] 探査機はやぶさ 2 のリュウグウ近傍探査の総括 (2019)
  • Author(s): 渡邊誠一郎ほか
  • Organizer: 日本惑星科学会秋季講演会 2019
• [Presentation] 小惑星リュウグウのクレーターと周辺ボルダーの関係に着目した表層の層構造の推定 (2019)
  • Author(s): 赤羽大貴、渡邊誠一郎、諸田智克ほか
  • Organizer: 日本惑星科学会秋季講演会 2019
• [Presentation] 小惑星 Ryugu の表面の色変化と層序 (2019)
  • Author(s): 諸田智克ほか
  • Organizer: 日本惑星科学会秋季講演会 2019
• [Presentation] An overview of Hayabusa2 mission and asteroid 162173 Ryugu (2019)
  • Author(s): Sei-ichiro Watanabe et al.
  • Organizer: Asteroid Science in the Age of Hayabusa20 and OSIRIS-Rex
  • Int'l Joint Research