Back at the end of 2020, two samples collected by the Hayabusa2 spacecraft of the asteroid Ryugu arrived here on Earth. The samples were divided up among several space agencies, with the majority staying with JAXA since the mission was theirs. In exchange for sharing with NASA, JAXA will receive a percentage of the sample returning from asteroid Bennu and the OSIRIS-REx mission, which should arrive in 2023.
Now, in a new paper published in Science and led by Tomoki Nakamura, an analysis of seventeen grains finds that the parent body of Ryugu likely formed about two million years after the formation of the solar system. Co-author Deborah Domingue explains: The goal of these initial studies is to understand and characterize Ryugu’s formation history. While the orbital data identified the presence of phyllosilicates, it was an analysis of the samples that gave us information on the detailed mineral composition and the physical properties of the regolith grains.
The region where Ryugu’s parent body formed was extremely cold, contained both water and carbon dioxide as solids, and likely was as far away from the Sun as Jupiter is now, if not somewhat farther. That parent body was then broken apart by a massive impact, resulting in the formation of one of two known asteroid families. Ryugu was a part of one of those families and then migrated inward to what is now the asteroid belt.
Furthermore, Ryugu was far from the initial impact site, as none of the minerals found showed signs of shock features. And Ryugu was made from assorted fragments that came from different depths of the parent body, resulting in its intriguing mineral and chemical makeup… and rubble pile consistency.
All of that was learned by sampling tiny rock fragments and doing some numerical modeling. Science is awesome.
JAXA press release
PSI press release
“Formation and evolution of carbonaceous asteroid Ryugu: Direct evidence from returned samples,” T. Nakamura et al., 2022 September 22, Science