The results were “very important,” said Victoria Hamilton, a scientist at the Southwest Research Institute in Boulder, Colo., who was not involved with the research. “Even though we’ve learned a lot about the early solar system from meteorites here on Earth, they lack any kind of context.”
In this case, planetary scientists know exactly where the samples came from.
The match of Ryugu with CI meteorites was unexpected because CI meteorites contain a lot of water, and Hayabusa2’s remote measurements while at Ryugu indicated the presence of some water but that the surface was mostly dry. The laboratory measurements, however, revealed about 7 percent water, said Dr. Tachibana, a co-author of the new Science study. That is a significant amount for such a mineral.
Dr. Tachibana said scientists were working on understanding the discrepancy.
The scientists also found some differences between the Ryugu samples and the Ivuna meteorite. The Ivuna meteorite included even higher amounts of water and contained minerals known as sulfates that were absent from Ryugu.
The differences could indicate how the mineralogy of the meteorite changed over decades sitting on Earth, absorbing water from the atmosphere and undergoing chemical reactions. That, in turn, could help scientists figure out what formed as part of the solar system 4.6 billion years ago and what changed recently in CI meteorites over a few decades on Earth.
“This shows why it’s important to go and have space missions, to go out and explore and bring back material in a really controlled way,” Dr. Russell said.
This also raises expectations for OSIRIS-REX’s Bennu samples, which will land in the Utah desert on Sept. 24, 2023. Dante Lauretta, the principal investigator of that mission, chose that asteroid in large part because it looked like it could be similar to CI meteorites, and OSIRIS-REX’s measurements at Bennu indicated more water than what Hayabusa2 observed at Ryugu. But if Ryugu is already a match for a CI meteorite, that suggests Bennu might be made of something different.
“So now I’m wondering, ‘What are we bringing back?’” said Dr. Lauretta, who was also an author on the Science paper. “It’s kind of exciting, but it’s also intellectually challenging.”