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

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Title: Population characteristics of submicrometer-sized craters on regolith particles from asteroid Itokawa
Authors: Matsumoto, Toru Browse this author
Hasegawa, S. Browse this author
Nakao, S. Browse this author
Sakai, M. Browse this author
Yurimoto, H. Browse this author →KAKEN DB
Issue Date: 15-Mar-2018
Publisher: Elsevier
Journal Title: Icarus
Volume: 303
Start Page: 22
End Page: 33
Publisher DOI: 10.1016/j.icarus.2017.12.017
Abstract: 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.
Type: article
Appears in Collections:理学院・理学研究院 (Graduate School of Science / Faculty of Science) > 雑誌発表論文等 (Peer-reviewed Journal Articles, etc)

Submitter: 圦本 尚義

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