Spectrally blue hydrated parent body of asteroid (162173) Ryugu

Ryugu is a carbonaceous rubble-pile asteroid visited by the Hayabusa2 spacecraft. Small rubble pile asteroids record the thermal evolution of their much larger parent bodies. However, recent space weathering and/or solar heating create ambiguities between the uppermost layer observable by remote-sensing and the pristine material from the parent body. Hayabusa2 remote-sensing observations find that on the asteroid (162173) Ryugu both north and south pole regions preserve the material least processed by space weathering, which is spectrally blue carbonaceous chondritic material with a 0–3% deep 0.7-µm band absorption, indicative of Fe-bearing phyllosilicates. Here we report that spectrally blue Ryugu's parent body experienced intensive aqueous alteration and subsequent thermal metamorphism at 570–670 K (300–400 °C), suggesting that Ryugu's parent body was heated by radioactive decay of short-lived radionuclides possibly because of its early formation 2–2.5 Ma. The samples being brought to Earth by Hayabusa2 will give us our first insights into this epoch in solar system history.

Eri Tatsumi, Naoya Sakatani, Lucie Riu, Moe Matsuoka, Rie Honda, Tomokatsu Morota, Shingo Kameda, Tomoki Nakamura, Michael Zolensky, Rosario Brunetto, Takahiro Hiroi, Sho Sasaki, Sei'ichiro Watanabe, Satoshi Tanaka, Jun Takita, Cédric Pilorget, Julia de León, Marcel Popescu, Juan Luis Rizos, Javier Licandro, Ernesto Palomba, Deborah Domingue, Faith Vilas, Humberto Campins, Yuichiro Cho, Kazuo Yoshioka, Hidehiko Suzuki, Chikatoshi Honda, Kazunori Ogawa, Kohei Kitazato, Naru Hirata, Naoyuki Hirata, Yuichi Tsuda, Makoto Yoshikawa, Takanao Saiki, Fuyuto Terui, Satoru Nakazawa, Yuto Takei, Hiroshi Takeuchi, Yukio Yamamoto, Tatsuaki Okada, Yuri Shimaki, Kei Shirai, Seiji Sugita