Journal Article

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

Nakazawa, Satoru, Nakamura, Eizo, Sawada, Hirotaka, Yabe, Yuna, Hirata, Naoyuki, Yoshitake, Miwa, Nakamura, Tomoki, Tsuda, Yuichi, Ogawa, Kazunori, Kobayashi, Katsura, Soejima, Hiromichi, Yogata, Kasumi, Namiki, Noriyuki, Okada, Tatsuaki, Kikuchi, Shota, Hirata, Naru, Shimada, Takanobu, Uesugi, Kentaro, Michikami, Tatsuhiro, Morota, Tomokatsu, Yamamoto, Yukio, Miura, Akira, Mimasu, Yuya, Yamamoto, Daiki, Ono, Go, Sugita, Seiji, Moussi-Soffys, Aurelie, Ireland, Trevor R., Saiki, Takanao, Kitazato, Kohei, Iwamae, Ayako, Takeuchi, Hiroshi, Noguchi, Rina, Yokota, Yasuhiro, Ogawa, Naoko, Senshu, Hiroki, Ikeda, Hitoshi, Lequertier, Guillaume, Ito, Motoo, Usui, Tomohiro, Kumagai, Kazuya, Tatsumi, Eri, Karouji, Yuzuru, Okazaki, Ryuji, Honda, Chikatoshi, Sakatani, Naoya, Kikuchi, Hiroshi, Yoshikawa, Makoto, Yumoto, Koki, Naraoka, Hiroshi, Pilorget, Cedric, Takano, Yoshinori, Loizeau, Damien, Miura, Yayoi N., Hirose, Chikako, Miyazaki, Akiko, Nishimura, Masahiro, Yano, Hajime, Noguchi, Takaaki, Mori, Osamu, Fujii, Atsushi, Takei, Yuto, Honda, Rie, Tsukizaki, Ryudo, Yabuta, Hikaru, Yamada, Tetsuya, Tanaka, Satoshi, Hosoda, Sato

2022

Overview

C-type asteroids 1 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 Ryugu 11 , 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 meteorites 12 , 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. The Hayabusa2 spacecraft returned 5.4 g of material from the asteroid Ryugu. A first analysis of the samples found an estimated density of 1,282 ± 231 kg m −3 , considerably lower than even the most porous meteorites. Together with preliminary spectral analysis, these results indicate that Ryugu is similar to CI chondrites, but darker, more porous and more brittle.

• Publisher: Nature Publishing Group UK,Nature Publishing Group
• Subject: 704/445/848 / 704/445/849 / Albedo / Asteroids / Astronomy / Astrophysics and Cosmology / Chemical properties / Letter / Meteors & meteorites / Physics / Physics and Astronomy / Porosity / Sciences of the Universe / Solar system / Spacecraft / Spectral analysis