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Population characteristics of submicrometer-sized craters on regolith particles from asteroid Itokawa


Icarus303 22–33.pdf3.75 MBPDF見る/開く

タイトル: Population characteristics of submicrometer-sized craters on regolith particles from asteroid Itokawa
著者: Matsumoto, Toru 著作を一覧する
Hasegawa, S. 著作を一覧する
Nakao, S. 著作を一覧する
Sakai, M. 著作を一覧する
Yurimoto, H. 著作を一覧する
発行日: 2018年 3月15日
出版者: Elsevier
誌名: Icarus
巻: 303
開始ページ: 22
終了ページ: 33
出版社 DOI: 10.1016/j.icarus.2017.12.017
抄録: We investigated impact crater structures on regolith particles from asteroid Itokawa using scanning electron microscopy. We observed the surfaces of 51 Itokawa particles, ranging from 15 mu m to 240 pm in size. Craters with average diameters ranging from 10 nm to 2.8 mu m were identified on 13 Itokawa particles larger than 80 mu m. We examined the abundance, spatial distribution, and morphology of approximately 900 craters on six Itokawa particles. Craters with sizes in excess of 200 nm are widely dispersed, with spatial densities from 2.6 mu m(2) to 4.5 mu m(2); a fraction of the craters was locally concentrated with a density of 0.1 mu m(2). The fractal dimension of the cumulative crater diameters ranges from 1.3 to 2.3. Craters of several tens of nanometers in diameter exhibit pit and surrounding rim structures. Craters of more than 100 nm in diameter commonly have melted residue at their bottom. These morphologies are similar to those of submicrometer-sized craters on lunar regolith. We estimated the impactor flux on Itokawa regolith-forming craters, assuming that the craters were accumulated during direct exposure to the space environment for 10(2) to 10(4) yr. The range of impactor flux onto Itokawa particles is estimated to be at least one order of magnitude higher than the interplanetary dust flux and comparable to the secondary impact flux on the Moon. This indicates that secondary ejecta impacts are probably the dominant cratering process in the submicrometer range on Itokawa regolith particles, as well as on the lunar surface. We demonstrate that secondary submicrometer craters can be produced anywhere in centimeter- to meter-sized depressions on ltokawa's surface through primary interplanetary dust impacts. If the surface unevenness on centimeter to meter scales is a significant factor determining the abundance of submicrometer secondary cratering, the secondary impact flux could be independent of the overall shapes or sizes of celestial bodies, and the secondary impact flux could have similar values on Itokawa and the Moon. (C) 2017 The Authors. Published by Elsevier Inc.
資料タイプ: article
出現コレクション:雑誌発表論文等 (Peer-reviewed Journal Articles, etc)

提供者: 圦本 尚義


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