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Surface morphological features of boulders on Asteroid 25143 Itokawa |
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| Authors: | Takaaki Noguchi Akira Tsuchiyama Hirohide Demura Hideaki Miyamoto Tomoki Nakamura Sho Sasaki Takashi Kubota Michael E Zolensky |
| Institution: | a College of Science, Ibaraki University, 2-1-1 Bunkyo, Mito, Ibaraki 310-8512, Japan b Department of Earth and Space Science, Osaka University, 1-1 Machikaneyama-cho, Toyonaka 560-0043, Japan c School of Computer Science and Engineering, University of Aizu, Fukushima 965-8580, Japan d National Institute of Advanced Industrial Science and Technology, Tsukuba 305-8568, Japan e University Museum, The University of Tokyo, Tokyo 113-0033, Japan f Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency, 3-1-1 Yoshinodai, Sagamihara, Kanagawa 229-8510, Japan g Department of Earth and Planetary Sciences, Faculty of Science, Kyushu University, Hakozaki, Fukuoka 812-8581, Japan h School of Engineering, Tokai University, Hiratsuka, Kanagawa 259-1292, Japan i Mizusawa Astrogeodynamics Observatory, National Astronomical Observatory of Japan, Iwate 023-0861, Japan j School of Earth Environmental Sciences, College of Natural Sciences, Seoul National University, Seoul 151-742, Republic of Korea k NASA Johnson Space Center, Houston, TX 77058, USA |
| Abstract: | On the sub-kilometer S-type asteroid, 25143 Itokawa, some boulders on rough terrains seem to be exposed without any powdery material covering. Based on surface morphological features, there are two major types of boulders: one has rounded edges and corners (rounded boulders), while the other has angular edges and corners (angular boulders). The surface features of the rounded boulders suggest that they have hardness heterogeneity and that some may be breccias. The angular boulders appear to be more resistant to impact disruption than the rounded ones, which may be due to a difference in lithology. The major constituents of Itokawa may be LL chondrite-like brecciated lithology (rounded boulders) along with a remarkable number of boulders suggesting that lithology is atypical among LL chondrites (angular boulders). Some of both types of boulders contain intersecting and stepped planar foliations. Comparison with meteorite ALH76009 suggests that the planar foliations may be marks where rocks were torn apart. As lithified breccias cannot be formed on present-day sub-kilometer-sized Itokawa, it is reasonable that boulders with various lithologies on Itokawa were formed on its large ancestor(s). The rubble-pile structure of Itokawa suggested by its low density (∼1.9 g/cm3) indicates that boulders on Itokawa are reassembled fragments formed by catastrophic disruption of large ancestor(s). |
| Keywords: | Asteroid Itokawa Regoliths Asteroids Surfaces |
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