Space environment of an asteroid preserved on micro - grains returned by the

Hayabusa spacecraft. Eizo Nakamura, A. Makishima, T. Moriguti, K. Kobayashi, R. Tanaka, T. Kunihiro, T. Tsujimori, C. Sakaguchi, H. Kitagawa, T. Ota, Y. Yachi, T. Yada, M. Abe, A. Fujimura, M. Ueno, T. Mukai, M. Yoshikawa, and J. Kawaguchi, The Pheasant Memorial Laboratory, Okayama University, Misasa, Tottori 682-0193, Japan ([email protected]), Japan Aerospace Exploration Agency Introduction: The Japan Aerospace Exploration Agency (JAXA) conducted the Hayabusa mission with the goal of better understanding solar system evolution through direct sampling of an asteroid and return of the samples to Earth for detailed analytical work. A target was set to the near-Earth asteroid 25143 Itokawa, an example of a spectral type-S asteroid common in the inner part of the asteroid belt. As a part of the mission, initial analyses of returned grains were carried out by several teams of researchers (see http://www.jaxa.jp/ press/2011/01/20110117_hayabusa_e.html). One team reported on the general properties of the grains and concluded that the building blocks of the rubble pile were identical to those of equilibrated LL ordinary-chondrites (OC) with mild overprinting by “space weathering” [1, 2, 3, 4]. This conclusion is consistent with the spectroscopic observations made from Earth and by the Hayabusa spacecraft [5, 6]; however, some key questions remain. What record of the environment at the asteroid exterior exists on the surface of grains deposited there and, more broadly, what were the most important processes shaping the post-accretion appearance of this asteroid? Nanometerscale investigation of the surfaces of these micro-grains can help us characterize the space environment of this and other asteroids, an important step toward more general understanding of impact phenomena in the inner solar system. In this paper, we report highlights of our initial analysis.