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Trace of Itokawa's Four Billion Years of History Found on Particles

June 22, 2016 (JST)

National Research and Development Agency
Japan Aerospace Exploration Agency (JAXA)

A research team led by Aerospace Project Research Associate Toru Matsumoto of the Japan Aerospace Exploration Agency (JAXA) found that traces of more than four billion years of history up until now of the Asteroid "Itokawa" were recoded on the surface of particles that were recovered from Itokawa by the Asteroid Explorer “Hayabusa” to bring back to the Earth, and their surface patterns and marks were analyzed by the research team.

The particles analyzed this time were just over 10 micrometers in size, and their surface patterns and marks were merely in nanometers (one millionth of one micrometer). The research team observed the faint structure of the particle surface in details through X-ray microtomography (X-ray CT) and by scanning electron microscopes. As a result, the surface pattern that had been believed to be just one type was found to be at least four variations.

One of them was found to stem from Itokawa's parent body. Asteroid Itokawa was not in its current shape from the beginning. When it was born over four billion years ago, it was a parent body about 40 times bigger (than current Itokawawa). The parent body was destroyed in fragments once, and it is believed that those fragments were assembled again to form Itokawa because some particles analyzed this time retain the pattern that was thought to be made over four billion years ago.

In addition to the above, we also found some patterns that were formed due to long-time exposure to solar wind or caused by friction between particles. Those patterns are shaped in a time scale of one million to thousand years. In other words, we can track the asteroid history by observing the particle surface.

The research method this time can acquire a lot of information without hurting the precious particles. Therefore, this method will become an imperative first-step analysis skill when studying extraterrestrial objects.

Magazine: Geochimica et Cosmochimica Acta (dated August 15, 2016)
Thesis title: Nanomorphology of Itokawa regolith particles: Application to space-weathering processes affecting the Itokawa asteroid
Authors: Toru Matsumoto, Akira Tsuchiyama, Kentaro Uesugi, Tsukasa Nakano, Masayuki Uesugi, Junya Matsuno, Takashi Nagano, Akira Shimada, Akihisa Takeuchi, Yoshio Suzuki, Tomoki Nakamura, Michihiko Nakamura, Arnold Gucsik, Keita Nagaki, Tatsuhiro Sakaiya, Tadashi Kondo
DOI No.: 10.1016/j.gca.2016.05.011