Ryugu Samples Reveal Asteroid’s Origin Story

An analysis of grains sampled from the asteroid Ryugu finds that the parent body likely formed about two million years after the formation of the solar system.

IMAGE: Sample catcher chamber A from the first touchdown of the Hayabusa2 spacecraft, captured by an optical microscope. Many particles larger than 1 millimeter were found in both chambers A and C. The particles in chamber C are typically bigger than those in chamber A. Chamber C material was gathered during the second touchdown, which is expected to contain subsurface material ejected from the creation of the artificial crater created during the first touchdown. CREDIT: JAXA

Didymos and Dimorphos may have all the current media attention, but let’s not forget that Hayabusa2 collected two samples from the asteroid Ryugu, which arrived back on Earth at the end of 2020. Wait… 2020 is over? When did that happen?

Anyway, the samples were divided up among several space agencies, with the majority staying with JAXA since the mission was theirs. NASA received a mere 23 grains about one millimeter in diameter as well as four containers of finer material. 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. Domingue notes: The mineralogy of the Ryugu samples is shown in this article to be…