Ryugu asteroid sheds light into the origins of the solar system
A study by a team of researchers at the University of California, Los Angeles (UCLA), using mineral samples collected from the Ryugu asteroid, has helped scientists understand the composition of our solar system. The samples analyzed were collected by Japan’s Hayabusa2 spacecraft, and the results have yielded information about the galaxy as it existed in its infancy, more than 4.5 billion years ago.
The research was recently published in the journal Nature Astronomy. The work was funded by Japan Aerospace Exploration Agency, NASA, and the National Science Foundation’s Instrumentation and Facilities program.
Results show the asteroid was formed early on
Researchers used isotopic analysis to find out how carbonate minerals from the asteroid were crystallized through reactions with water. According to the team, this is believed to have originally accreted to the asteroid as ice in the still-forming solar system, then warmed into liquid. These carbonates are likely to have developed very early on, "within the first 1.8 million years of the solar system’s existence — and they preserve a record of the temperature and composition of the asteroid’s aqueous fluid as it existed at that time," said a news release.
"The Ryugu samples tell us that the asteroid and similar objects formed relatively rapidly in the outer solar system, beyond the condensation fronts of water and carbon dioxide ices, probably as small bodies,” said Kevin McKeegan, co-author of the study and a professor of Earth, planetary and space sciences at UCLA.
Ryugu likely to be a small asteroid
The age of carbonates found, estimated to be formed several million years earlier than previously thought, indicates that Ryugu probably broke from a small asteroid or object, "probably less than 12.5 miles (20 kilometers) in diameter."
According to the team, the result is surprising as "most models of asteroid accretion would predict assembly over longer periods, resulting in the formation of bodies at least 30 miles (more than 50 kilometers) in diameter." This could in turn, help them to survive various collisions over the long history of the solar system.
As Ryugu is only about one kilometer in diameter due to collisions and reassembly throughout its history, researchers said it is very unlikely to have been a large asteroid.
The team said that any larger asteroid formed very early on in the solar system would have undergone intensive chemical differentiation due to high temperatures. "Ryugu shows no evidence of that, and its chemical and mineralogical compositions are equivalent to those found in the most chemically primitive meteorites, the so-called CI chondrites, which are also thought to have formed in the outer solar system."
The team hopes that the ongoing research on the Ryugu materials will help answer astrobiology questions by understanding volatile- and carbon-rich asteroids. Such efforts will "continue to open a window into the formation of the solar system’s planets, including Earth."
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 and 20 °C and enriched in 13C, 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 approximately the first 1.8 million years of Solar System history, requiring early accretion either in a planetesimal less than ∼20 km in diameter or within a larger body that was disrupted and reassembled.
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