地球に戻ってきた小惑星からのサンプルは、水の源と生命の構成要素の可能性を明らかにする

太陽系外縁部からの小惑星が生命の構成要素を地球にもたらした可能性があります。

新しい研究により、地球を含む太陽系内部がどのようにして水と豊富な有機成分 – すべての生命の構成要素 – を獲得したかについての重要な新しい手がかりが明らかになりました。

高知チーム² 彼は、小惑星「リュウグウ」から地球に戻ってきた8つの粒子の詳細な研究を行いました.[{” attribute=””>JAXA³ spacecraft Hayabusa2. They are supported by researchers at The Open University (OU) and the University of California, Los Angeles (UCLA), USA and led by Motoo Ito of JAMSTEC. It was published on August 15, 2022, in Nature Astronomy.

Most pristine solar system samples ever

Experts from the OU undertook oxygen isotope analysis on samples from Ryugu. They used data that was a critical component in establishing the links between the returned asteroid materials and the existing meteorite record.

Based on spacecraft data, it was previously thought that the Ryugu material had experienced high temperatures. Because of this, most of the water it contained was believed to have been driven off. This theory was discovered to be incorrect.

Asteroids from the outer Solar System may have brought the building blocks of life to Earth. Credit: Phase2 Kochi/JAXA

In fact, the material contains a lot of water and organic matter. OU experts were able to confirm that the Ryugu samples are very similar to meteorites of the CI (Ivuna-type) chondrite group. These are considered the most important single meteorite group because they have a composition that matches that of our Solar System. They were also able to show that CI chondrites have been contaminated by their interaction with the terrestrial environment.

Because the Ryugu samples were collected and returned to Earth in ultra-clean conditions, they are the most pristine, primitive Solar System samples that we have.

‘More precious than gold dust’

The OU team was comprised of Richard Greenwood, Ross Findlay, Ian Franchi, and James Malley.

Richard Greenwood is a Research Fellow at the OU and supported the study through isotope analysis. Dr. Greenwood explained the importance of the research:

“When Asteroid Ryugu was surveyed in space by the Haybusa2 spacecraft it looked as though the results from the mission might be a bit disappointing. It seemed that materials from which the asteroid was composed had been heated to a high temperature and much of the water stored in them had been lost to space.

“However, while working as part of the Japanese Kochi Team, OU scientists were able to demonstrate that the Ryugu samples were closely similar to the important and unheated CI (Ivuna-type) chondrites. These are materials that have a composition that closely matches that of the Solar System itself, including the Sun. For understanding the chemistry of the Solar System it turns out that the Ryugu materials are more precious gold dust.”

Despite the material from Ryugu being aqueous (of or containing water), low temperatures mean the primary relationships between its minerals and the organic component have been preserved. Isotopic evidence (hydrogen and nitrogen) indicates that the fine-grained minerals and organics seen in the Ryugu particles formed in the outer Solar System.

Because of this study, experts have been able to conclude that materials in primitive asteroids may have acted as ‘cradles’ for organic molecules. This would have helped to preserve them and so provides a potential mechanism for the coupled delivery of water and organics to the early Earth.

Reference: “A pristine record of outer Solar System materials from asteroid Ryugu’s returned sample” by Motoo Ito, Naotaka Tomioka, Masayuki Uesugi, Akira Yamaguchi, Naoki Shirai, Takuji Ohigashi, Ming-Chang Liu, Richard C. Greenwood, Makoto Kimura, Naoya Imae, Kentaro Uesugi, Aiko Nakato, Kasumi Yogata, Hayato Yuzawa, Yu Kodama, Akira Tsuchiyama, Masahiro Yasutake, Ross Findlay, Ian A. Franchi, James A. Malley, Kaitlyn A. McCain, Nozomi Matsuda, Kevin D. McKeegan, Kaori Hirahara, Akihisa Takeuchi, Shun Sekimoto, Ikuya Sakurai, Ikuo Okada, Yuzuru Karouji, Masahiko Arakawa, Atsushi Fujii, Masaki Fujimoto, Masahiko Hayakawa, Naoyuki Hirata, Naru Hirata, Rie Honda, Chikatoshi Honda, Satoshi Hosoda, Yu-ichi Iijima, Hitoshi Ikeda, Masateru Ishiguro, Yoshiaki Ishihara, Takahiro Iwata, Kosuke Kawahara, Shota Kikuchi, Kohei Kitazato, Koji Matsumoto, Moe Matsuoka, Tatsuhiro Michikami, Yuya Mimasu, Akira Miura, Osamu Mori, Tomokatsu Morota, Satoru Nakazawa, Noriyuki Namiki, Hirotomo Noda, Rina Noguchi, Naoko Ogawa, Kazunori Ogawa, Tatsuaki Okada, Chisato Okamoto, Go Ono, Masanobu Ozaki, Takanao Saiki, Naoya Sakatani, Hirotaka Sawada, Hiroki Senshu, Yuri Shimaki, Kei Shirai, Seiji Sugita, Yuto Takei, Hiroshi Takeuchi, Satoshi Tanaka, Eri Tatsumi, Fuyuto Terui, Ryudo Tsukizaki, Koji Wada, Manabu Yamada, Tetsuya Yamada, Yukio Yamamoto, Hajime Yano, Yasuhiro Yokota, Keisuke Yoshihara, Makoto Yoshikawa, Kent Yoshikawa, Ryota Fukai, Shizuho Furuya, Kentaro Hatakeda, Tasuku Hayashi, Yuya Hitomi, Kazuya Kumagai, Akiko Miyazaki, Masahiro Nishimura, Hiromichi Soejima, Ayako Iwamae, Daiki Yamamoto, Miwa Yoshitake, Toru Yada, Masanao Abe, Tomohiro Usui, Sei-ichiro Watanabe and Yuichi Tsuda, 15 August 2022, Nature Astronomy.
DOI: 10.1038/s41550-022-01745-5