Space environment of an asteroid preserved on micrograins returned by the Hayabusa spacecraft

作者：Nakamura Eizo^*; Makishima Akio; Moriguti Takuya; Kobayashi Katsura; Tanaka Ryoji; Kunihiro Tak; Tsujimori Tatsuki; Sakaguchi Chie; Kitagawa Hiroshi; Ota Tsutomu; Yachi Yusuke; Yada Toru; Abe Masanao; Fujimura Akio; Ueno Munetaka; Mukai Toshifumi; Yoshikawa Makoto; Kawaguchi Jun' ichiro

来源：Proceedings of the National Academy of Sciences, 2012, 109(11): E624-E629.

DOI：10.1073/pnas.1116236109

• impacts
• sample-return mission
• interplanetary dust
• space weathering
• comprehensive analysis

Records of micrometeorite collisions at down to submicron scales were discovered on dust grains recovered from near-Earth asteroid 25143 (Itokawa). Because the grains were sampled from very near the surface of the asteroid, by the Hayabusa spacecraft, their surfaces reflect the low-gravity space environment influencing the physical nature of the asteroid exterior. The space environment was examined by description of grain surfaces and asteroidal scenes were reconstructed. Chemical and O isotope compositions of five lithic grains, with diameters near 50 mu m, indicate that the uppermost layer of the rubble-pile-textured Itokawa is largely composed of equilibrated LL-ordinary-chondrite-like material with superimposed effects of collisions. The surfaces of the grains are dominated by fractures, and the fracture planes contain not only sub-mu m-sized craters but also a large number of sub-mu m-to several-mu m-sized adhered particles, some of the latter composed of glass. The size distribution and chemical compositions of the adhered particles, together with the occurrences of the sub-mu m-sized craters, suggest formation by hypervelocity collisions of micrometeorites at down to nm scales, a process expected in the physically hostile environment at an asteroid%26apos;s surface. We describe impact-related phenomena, ranging in scale from 10(-9) to 10(4) meters, demonstrating the central role played by impact processes in the long-term evolution of planetary bodies. Impact appears to be an important process shaping the exteriors of not only large planetary bodies, such as the moon, but also low-gravity bodies such as asteroids.

• 出版日期2012-3-13