Evolving planets get a bumpy ride
Asteroids are considered to comprise intermediate products in the evolution of solar bodies. The Japan Aerospace Exploration Agency (JAXA) sent a probe to investigate the near-Earth asteroid 25143 Itokawa with the aim of learning more about the evolution of the solar system. Eizo Nakamura and colleagues at Okayama University and the Japan Aerospace Exploration Agency (JAXA) have now studied samples retrieved by the probe — the first reported analysis of grains taken directly from a solar body in space.
Using scanning electron microscopy, the researchers identified craters 100-200 nm in size as well as particles adhered to the asteroid surface. They suggest that a combination of disaggregation, cratering, melting, adhesion, agglutination, and implantation/sputtering affect the asteroid surface as a result of bombardment by submicrometre sized particles in space.
Among the other features observed in the grains a type of feldspar occurrence would have formed during slow cooling from temperatures of 860 °C. These temperatures and cooling dynamics could not have been achieved in a rock with a radius of only 300m. As a result it is likely that the asteroid Itokawa originated from a larger asteroid.
"We suggest that the chemistry and textures of Itokawa's surface reflect long-term bombardment of equilibrated chondritic material, at scales of 10−9 to 104 meters," conclude the authors. They add that impact processes in general play a central role in the evolution of planetary bodies.
・ Authors: Eizo Nakamura1, Akio Makishima1, Takuya Moriguti1, Katsura Kobayashi1, Ryoji Tanaka1, Tak Kunihiro1, Tatsuki Tsujimori1, Chie Sakaguchi1, Hiroshi Kitagawa1, Tsutomu Ota1, Yusuke Yachi1, Toru Yada2, Masanao Abe2, Akio Fujimura2, Munetaka Ueno2, Toshifumi Mukai2, Makoto Yoshikawa2, and Jun'ichiro Kawaguchi2
・ Title of original paper: Space environment of an asteroid preserved on micrograins returned by the Hayabusa spacecraft
・ Journal, volume, pages and year: Proceedings of the National Academy of Science 109, E624-E629 (2012).
・ Digital Object Identifier (DOI): 10.1073/pnas.1116236109
1 The Pheasant Memorial Laboratory for Geochemistry and Cosmochemistry, Institute for Study of the Earth's Interior, Okayama University, Misasa, Tottori 682-0193, Japan.
2 Japan Aerospace Exploration Agency, Yoshinodai 3-1-1, Chuo, Sagamihara, Kanagawa 252-5210, Japan.