Development of a crater scale law on a small body regolith by microgravity experiments

2021 Fiscal Year Final Research Report

• Project/Area Number: 18K03723
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Multi-year Fund
• Section: 一般
• Review Section: Basic Section 17010:Space and planetary sciences-related
• Research Institution: Kobe University
• Principal Investigator: Nakamura Akiko 神戸大学, 理学研究科, 准教授 (40260012)
• Co-Investigator(Kenkyū-buntansha): 和田 浩二 千葉工業大学, 惑星探査研究センター, 主席研究員 (10396856) ; 長谷川 直 国立研究開発法人宇宙航空研究開発機構, 宇宙科学研究所, 主任研究開発員 (10399553)
• Project Period (FY): 2018-04-01 – 2022-03-31
• Keywords: 低重力 / クレーター / レゴリス

Outline of Final Research Achievements

We develop a drop tower for the target container of cratering experiment and performed impact cratering experiments under simulated low-gravity conditions. The crater diameters of silica sand targets of several hundred microns in size were larger under low gravity than under 1 G, indicating that the dependence on the gravitational acceleration is consistent with the values shown in previous studies. For the strongly adherent, several tens of microns size particle targets, there was no significant difference in crater diameters under 1 G and under low gravity, i.e., the "inter-particle force dominated regime" in crater formation was confirmed. On the other hand, we measured microscopic particle shape and inter-particle cohesive forces of meteorite powder, which is considered to be equivalent to asteroid regolith, and showed that it is coarser and has smaller cohesive forces than silica sand and other materials used in cratering experiments as simulated regolith.

Free Research Field

惑星科学

Academic Significance and Societal Importance of the Research Achievements

はやぶさ２が探査した小惑星リュウグウや、これからMMXによって探査される火星衛星フォボスは、岩塊や砂状のレゴリスで表面が覆われている。これらの天体表層は、地上に比べて数桁も重力加速度が小さい。しかし、微小重力の天体表面ではレゴリス粒子同士の付着性が無視できない可能性がある。本研究は、模擬低重力下でクレーター実験を行うシステムを開発し、クレーターの大きさについてレゴリスの付着性がどのように影響するかを実験的に示した。