Formation and evolution of carbonaceous asteroid Ryugu: Direct evidence from returned samples
Tomoki Nakamura, Megumi Matsumoto, Kana Amano, Yuma Enokido, M. E. Zolensky, T. Mikouchi, Hidenori Genda, Satoshi Tanaka, M. Yu. Zolotov, Kosuke Kurosawa, Shigeru Wakita, Ryuki Hyodo, Hosei Nagano, D. Nakashima, Yoshio Takahashi, Yuri Fujioka, Mizuha Kikuiri, Eiichi Kagawa, M. Matsuoka, A. J. Brearley, A. Tsuchiyama, Masayuki Uesugi, Junya Matsuno, Yuki Kimura, Masahiko Sato, R. E. Milliken, Eri Tatsumi, Seiji Sugita, T. Hiroi, K. Kitazato, D. E. Brownlee, D. J. Joswiak, Masaki Takahashi, Kazuhiko Ninomiya, Tadayuki Takahashi, Takahito Osawa, Kentaro Terada, Frank E. Brenker, B. J. Tkalcec, László Vincze, R. Brunetto, Alice Aléon‐Toppani, Q. H. S. Chan, Mathieu Roskosz, Jean‐Christophe Viennet, Pierre Beck, E. E. Alp, Tatsuhiro Michikami, Yuuya Nagaashi, Takeshi Tsuji, Yuta Ino, J. Martinez, J. Han, Andrei Dolocan, Robert J. Bodnar, M. Tanaka, Hideto Yoshida, K. Sugiyama, A. J. King, Keisuke Fukushi, Hiroki Suga, Shohei Yamashita, T. Kawai, Kumiko Inoue, Aiko Nakato, T. Noguchi, F. Vilas, Amanda Hendrix, Camilo Jaramillo, D. L. Domingue, G. Domínguez, Z. Gainsforth, C. Engrand, J. Duprat, S. S. Russell, Enrica Bonato, Chi Ma, Tatsuhiko Kawamoto, Takehiko Wada, Sei‐ichiro Watanabe, Rie Endo, Satomi Enju, Lucie Riu, Stefano Rubino, Pieter Tack, Soshi Takeshita, Yasuo Takeichi, Akihisa Takeuchi, Aki Takigawa, D. Takir, Toshiaki Tanigaki, Atsushi Taniguchi, Katsuo Tsukamoto, Takashi Yagi, S. Yamada, Kazuo Yamamoto, Yuichiro Yamashita, Masahiro Yasutake, Kentaro Uesugi, Izumi Umegaki
Abstract
Samples of the carbonaceous asteroid Ryugu were brought to Earth by the Hayabusa2 spacecraft. We analyzed 17 Ryugu samples measuring 1 to 8 millimeters. Carbon dioxide-bearing water inclusions are present within a pyrrhotite crystal, indicating that Ryugu's parent asteroid formed in the outer Solar System. The samples contain low abundances of materials that formed at high temperatures, such as chondrules and calcium- and aluminum-rich inclusions. The samples are rich in phyllosilicates and carbonates, which formed through aqueous alteration reactions at low temperature, high pH, and water/rock ratios of <1 (by mass). Less altered fragments contain olivine, pyroxene, amorphous silicates, calcite, and phosphide. Numerical simulations, based on the mineralogical and physical properties of the samples, indicate that Ryugu's parent body formed ~2 million years after the beginning of Solar System formation.