Early fluid activity on Ryugu: perspectives from oxygen, carbon, and 53Mn-53Cr isotopes

Abstract Samples from asteroid Ryugu returned by the Hayabusa2 mission contain evidence of extensive alteration by aqueous fluids and appear related to the CI chondrites. To understand the sources of the fluid and the timing of chemical reactions occurring during the alteration processes, we investigated the oxygen, carbon, and 53Mn-53Cr systematics of carbonate and magnetite in two Ryugu particles. We find that the fluid was initially between 0 − 20°C and enriched in 13C, and 17O and 18O, and subsequently evolved towards lighter carbon and oxygen isotopic compositions as alteration proceeded. Carbonate ages show that this fluid-rock interaction took place within the first ~ 1.4 million years of solar system history requiring early accretion and preservation of carbonaceous material, either in a planetesimal less than ~ 17 km in diameter or a larger body which was disrupted and reassembled.