Preliminary analysis of the Hayabusa2 samples returned from C-type asteroid Ryugu

Toru Yada , Masanao Abe , Tatsuaki Okada , Aiko Nakato , Kasumi Yogata , Akiko Miyazaki , Kentaro Hatakeda , Kazuya Kumagai , Masahiro Nishimura , Yuya Hitomi , Hiromichi Soejima , Miwa Yoshitake , Ayako Iwamae , Shizuho Furuya , Masayuki Uesugi , Yuzuru Karouji , Tomohiro Usui , Tasuku Hayashi , Daiki Yamamoto , Ryota Fukai , Seiji Sugita , Yuichiro Cho , Koki Yumoto , Yuna Yabe , Jean-Pierre Bibring (1) , Cedric Pilorget (1) , Vincent Hamm (1) , Rosario Brunetto (1) , Lucie Riu (1) , Lionel Lourit (1) , Damien Loizeau (1) , Guillaume Lequertier (1) , Aurelie Moussi-Soffys (2) , Shogo Tachibana , Hirotaka Sawada , Ryuji Okazaki , Yoshinori Takano , Kanako Sakamoto , Yayoi N. Miura , Hajime Yano , Trevor R. Ireland , Tetsuya Yamada , Masaki Fujimoto , Kohei Kitazato , Noriyuki Namiki , Masahiko Arakawa , Naru Hirata , Hisayoshi Yurimoto , Tomoki Nakamura , Takaaki Noguchi , Hikaru Yabuta , Hiroshi Naraoka , Motoo Ito , Eizo Nakamura , Kentaro Uesugi , Katsura Kobayashi , Tatsuhiro Michikami , Hiroshi Kikuchi , Naoyuki Hirata , Yoshiaki Ishihara , Koji Matsumoto , Hirotomo Noda , Rina Noguchi , Yuri Shimaki , Kei Shirai , Kazunori Ogawa , Koji Wada , Hiroki Senshu , Yukio Yamamoto , Tomokatsu Morota , Rie Honda , Chikatoshi Honda , Yasuhiro Yokota , Moe Matsuoka (3) , Naoya Sakatani , Eri Tatsumi , Akira Miura , Manabu Yamada , Atsushi Fujii , Chikako Hirose , Satoshi Hosoda , Hitoshi Ikeda , Takahiro Iwata , Shota Kikuchi , Yuya Mimasu , Osamu Mori , Naoko Ogawa , Go Ono , Takanobu Shimada , Stefania Soldini , Tadateru Takahashi , Yuto Takei , Hiroshi Takeuchi , Ryudo Tsukizaki , Kent Yoshikawa , Fuyuto Terui , Satoru Nakazawa , Satoshi Tanaka , Takanao Saiki , Makoto Yoshikawa , Sei-Ichiro Watanabe , Yuichi Tsuda

1 IAS - Institut d'astrophysique spatiale
2 CNES - Centre National d'Études Spatiales [Toulouse]
3 Observatoire de Paris

C-type asteroids¹ are considered to be primitive small Solar System bodies enriched in water and organics, providing clues to the origin and evolution of the Solar System and the building blocks of life. C-type asteroid 162173 Ryugu has been characterized by remote sensing^2-7 and on-asteroid measurements^8,9 with Hayabusa2 (ref. ¹⁰). However, the ground truth provided by laboratory analysis of returned samples is invaluable to determine the fine properties of asteroids and other planetary bodies. We report preliminary results of analyses on returned samples from Ryugu of the particle size distribution, density and porosity, spectral properties and textural properties, and the results of a search for Ca-Al-rich inclusions (CAIs) and chondrules. The bulk sample mainly consists of rugged and smooth particles of millimetre to submillimetre size, confirming that the physical and chemical properties were not altered during the return from the asteroid. The power index of its size distribution is shallower than that of the surface boulder observed on Ryugu¹¹, indicating differences in the returned Ryugu samples. The average of the estimated bulk densities of Ryugu sample particles is 1,282 ± 231 kg m⁻³, which is lower than that of meteorites¹², suggesting a high microporosity down to the millimetre scale, extending centimetre-scale estimates from thermal measurements^5,9. The extremely dark optical to near-infrared reflectance and spectral profile with weak absorptions at 2.7 and 3.4 μm imply a carbonaceous composition with indigenous aqueous alteration, matching the global average of Ryugu^3,4 and confirming that the sample is representative of the asteroid. Together with the absence of submillimetre CAIs and chondrules, these features indicate that Ryugu is most similar to CI chondrites but has lower albedo, higher porosity and more fragile characteristics.

Domains: Sciences of the Universe [physics]

Toru Yada, Masanao Abe, Tatsuaki Okada, Aiko Nakato, Kasumi Yogata, et al.. Preliminary analysis of the Hayabusa2 samples returned from C-type asteroid Ryugu. Nature Astronomy, 2021, 6, pp.214-220. ⟨10.1038/s41550-021-01550-6⟩. ⟨insu-03744514⟩