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Originally published in Science Express on 19 April 2007
Science 18 May 2007:
Vol. 316. no. 5827, pp. 1011 - 1014
DOI: 10.1126/science.1134390
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Reports

Regolith Migration and Sorting on Asteroid Itokawa

Hideaki Miyamoto,1,2,3,4* Hajime Yano,5 Daniel J. Scheeres,6 Shinsuke Abe,7 Olivier Barnouin-Jha,8 Andrew F. Cheng,8 Hirohide Demura,9 Robert W. Gaskell,10 Naru Hirata,9 Masateru Ishiguro,11 Tatsuhiro Michikami,12 Akiko M. Nakamura,7 Ryosuke Nakamura,13 Jun Saito,5,14 Sho Sasaki15

High-resolution images of the surface of asteroid Itokawa from the Hayabusa mission reveal it to be covered with unconsolidated millimeter-sized and larger gravels. Locations and morphologic characteristics of this gravel indicate that Itokawa has experienced considerable vibrations, which have triggered global-scale granular processes in its dry, vacuum, microgravity environment. These processes likely include granular convection, landslide-like granular migrations, and particle sorting, resulting in the segregation of the fine gravels into areas of potential lows. Granular processes become major resurfacing processes because of Itokawa's small size, implying that they can occur on other small asteroids should those have regolith.

1 Department of Museum Collection Utilization Studies, The University Museum, University of Tokyo, Hongo 7-3-1, Bunkyoku, Tokyo 113-0033, Japan.
2 Department of Earth and Planetary Science, University of Tokyo, Hongo 7-3-1, Bunkyoku, Tokyo 113-0033, Japan.
3 Department of Geosystem Engineering, University of Tokyo, Hongo 7-3-1, Bunkyo-ku, Tokyo 113-8656, Japan.
4 Planetary Science Institute, 1700 East Fort Lowell Road, Suite 106, Tucson, AZ 85719, USA.
5 Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency, 3-1-1 Yoshinodai, Sagamihara, Kanagawa 229-8510, Japan.
6 Department of Aerospace Engineering, University of Michigan, Ann Arbor, MI 48109, USA.
7 Graduate School of Science and Technology, Kobe University, 1-1 Rokkodai-cho, Nada-ku, Kobe 657-8501, Japan.
8 Johns Hopkins University Applied Physics Laboratory, Laurel, MD 20723, USA.
9 Department of Computer Software, University of Aizu, Ikki-machi, Aizu-Wakamatsu City, Fukushima 965-8580, Japan.
10 Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109, USA.
11 Astronomy Department, Seoul National University, Seoul 151-747, Korea.
12 Fukushima National College of Technology, Iwaki 970-8034, Japan.
13 National Institute of Advanced Industrial Science and Technology, Tsukuba 306-8568, Japan.
14 School of Engineering, Tokai University, Hiratsuka, Kanagawa 259-1292, Japan.
15 Research in Selenodesy Project Office, National Astronomical Observatory of Japan, 2-12 Hoshigaoka, Mizusawa, Oshu 023-0861, Japan.

* To whom correspondence should be addressed. E-mail: hm{at}um.u-tokyo.ac.jp

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Science. ISSN 0036-8075 (print), 1095-9203 (online)