Preliminary analysis of the Hayabusa2 samples returned from C-type asteroid Ryugu
Authors: Yada Toru , Abe Masanao , Okada Tatsuaki , Nakato Aiko , Yogata Kasumi , Miyazaki Akiko , Hatakeda Kentaro , Kumagai Kazuya , Nishimura Masahiro , Hitomi Yuya , Soejima Hiromichi , Yoshitake Miwa , Iwamae Ayako , Furuya Shizuho , Uesugi Masayuki , Karouji Yuzuru , Usui Tomohiro , Hayashi Tasuku , Yamamoto Daiki , Fukai Ryota , Sugita Seiji , Cho Yuichiro , Yumoto Koki , Yabe Yuna , Bibring Jean-Pierre , Pilorget Cedric , Hamm Vincent , Brunetto Rosario , Riu Lucie , Lourit Lionel , Loizeau Damien , Lequertier Guillaume , Moussi-Soffys Aurelie , Tachibana Shogo , Sawada Hirotaka , Okazaki Ryuji , Takano Yoshinori , Sakamoto Kanako , Miura Yayoi N. , Yano Hajime , Ireland Trevor R. , Yamada Tetsuya , Fujimoto Masaki , Kitazato Kohei , Namiki Noriyuki , Arakawa Masahiko , Hirata Naru , Yurimoto Hisayoshi , Nakamura Tomoki , Noguchi Takaaki , Yabuta Hikaru , Naraoka Hiroshi , Ito Motoo , Nakamura Eizo , Uesugi Kentaro , Kobayashi Katsura , Michikami Tatsuhiro , Kikuchi Hiroshi , Hirata Naoyuki , Ishihara Yoshiaki , Matsumoto Koji , Noda Hirotomo , Noguchi Rina , Shimaki Yuri , Shirai Kei , Ogawa Kazunori , Wada Koji , Senshu Hiroki , Yamamoto Yukio , Morota Tomokatsu , Honda Rie , Honda Chikatoshi , Yokota Yasuhiro , Matsuoka Moe , Sakatani Naoya , Tatsumi Eri , Miura Akira , Yamada Manabu , Fujii Atsushi , Hirose Chikako , Hosoda Satoshi , Ikeda Hitoshi , Iwata Takahiro , Kikuchi Shota , Mimasu Yuya , Mori Osamu , Ogawa Naoko , Ono Go , Shimada Takanobu , Soldini Stefania , Takahashi Tadateru , Takei Yuto , Takeuchi Hiroshi , Tsukizaki Ryudo , Yoshikawa Kent , Terui Fuyuto , Nakazawa Satoru , Tanaka Satoshi , Saiki Takanao , Yoshikawa Makoto , Watanabe Sei-ichiro , Tsuda Yuichi 
Published: December 2021

AbstractC-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 sensing2–7 and on-asteroid measurements8,9 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 measurements5,9. 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 Ryugu3,4 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.