Earth Planets Space, Vol. 60 (No. 1), pp. 7-12, 2008
A. M. Nakamura1, T. Michikami2, N. Hirata3, A. Fujiwara4, R. Nakamura5, M. Ishiguro6, H. Miyamoto7,8, H. Demura3, K. Hiraoka1, T. Honda1, C. Honda4, J. Saito9, T. Hashimoto4, and T. Kubota4
1Graduate School of Science, Kobe University, Kobe, 657-8501, Japan
2Fukushima National College of Technology, Iwaki, Fukushima 970-8034, Japan
3School of Computer Science and Engineering, University of Aizu, Aizuwakamatsu, Fukushima 965-8580, Japan
4Institute of Space and Astronautical Sciences (ISAS), Japan Aerospace Exploration Agency (JAXA), Sagamihara, Kanagawa 229-8510, Japan
5National Institute of Advanced Industrial Science and Technology, Tsukuba 306-8568, Japan
6Astronomy Department, Seoul National University, Seoul 151-747, Korea
7The University Museum, University of Tokyo, Tokyo 113-0033, Japan
8Planetary Science Institute, Tucson, AZ 85719, USA
9School of Engineering, Tokai University, Hiratsuka, Kanagawa 259-1292, Japan
(Received November 3, 2006; Revised March 29, 2007; Accepted April 11, 2007; Online published February 12, 2008)
The subkilometer-size asteroid 25143 Itokawa is considered to have a gravitationally bounded rubble-pile structure. Boulders appearing in high-resolution images retrieved by the Hayabusa mission revealed the genuine outcome of the collisional event involving the asteroid's parent body. Here we report that the boulders' shapes and structures are strikingly similar to laboratory rock impact fragments despite differences of orders of magnitude in scale and complexities of the physical processes. These similarities suggest the universal character of the process throughout the range of these scales, and the brittle and structurally continuous nature regarding the parent body of the boulders. The similarity was likely preserved because of relatively lesser comminuting processes acting on individual boulders; the close assemblages of similar appearing boulders (a boulder family) represent the impact destruction of boulders on the surface.
Key words: Asteroid, boulder, impact, fragmentation.