2022 Fiscal Year Final Research Report
Formation and topographic relaxation of spinning top-shaped asteroids
| Project/Area Number |
19H01951
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| Research Category |
Grant-in-Aid for Scientific Research (B)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Review Section |
Basic Section 17010:Space and planetary sciences-related
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| Research Institution | Nagoya University |
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Principal Investigator |
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| 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)
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| Project Period (FY) |
2019-04-01 – 2022-03-31
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| 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 |
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| 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.
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| Free Research Field |
惑星科学
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| 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。
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