How was the solar system formed? The Ryugu asteroid helps us learn


How was the solar system formed?  The Ryugu asteroid helps us learn

Credit: Japan Aerospace Exploration Agency (JAXA)

Mineral samples collected from asteroid Ryugu by the Japanese spacecraft Hayabusa2 are helping astronomers and their colleagues at UCLA better understand the chemical makeup of our solar system as it existed in its infancy, more than 4.5 billion years ago.

In research recently published in natural astronomyand scientists using Isotope analysis Explore this carbonate minerals From the asteroid through interactions with water, which originally accumulated on the asteroid as ice in the still-forming solar system, then warmed to a liquid. They say these carbonates formed very early — during the first 1.8 million years of the solar system’s existence — and they hold a record of the temperature and composition of the asteroid’s liquid-water as it existed at the time.

said study co-author Kevin McKeegan, Distinguished Professor of Earth, Planetary and Space Sciences at UCLA. He noted that what makes Ryugu special is that, unlike meteorites, it had no potential contact with Earth. By analyzing the chemical signatures in the samples, scientists can develop a picture of not only how but where Ryugu formed.

“The Ryugu samples tell us that the asteroid and similar objects formed relatively quickly in the outer solar system, outside fronts of water and carbon dioxide condensation, possibly as small bodies,” McKegan said.

The researchers’ analysis determined that the Ryugu carbonate formed several million years earlier than previously thought, and indicated that Ryugu — or the progenitor asteroid from which it may have broken away — accreted as a relatively small body, perhaps less than 20 kilometers (12.5 miles) in diameter.

This result is surprising, McKegan said, because most asteroid accretion models would predict aggregation at longer periods, creating bodies at least 50 kilometers (more than 30 miles) in diameter that could better survive collision evolution over the solar system’s long history. .

The Hayabusa2 spacecraft lands on Ryugu on July 1, 2019 to collect samples. Hayabusa2 flew over the Earth in December 2020 and dropped samples in the Australian outback. Researchers have spent the past year studying it. Credit: JAXA, University of Tokyo, Kochi University, Rikkyo University, Nagoya University, Chiba Institute of Technology, Meiji University, Aizu University, AIST

The researchers said that while Ryugu is currently only 1 km in diameter as a result of collisions and re-assemblies throughout its history, it is very unlikely that it will ever be a large asteroid. They noted that any larger asteroid that forms very early in the solar system might be heated to high temperatures due to the decay of large amounts of aluminum-26, a radionuclide, which leads to the melting of rocks throughout the interior of the asteroid, along with chemicals. Differentiation, such as separation of minerals and silicates.

Ryugu shows no evidence of this, and its chemical and mineralogical composition is equivalent to that of more chemically primitive meteorites, the so-called CI chondrites, which are also thought to have formed in the outer solar system.

Ongoing research on Ryugu’s materials will continue to open a window on the formation of the solar system’s planets, McKeegan said, including Earth.

“Improving our understanding of volatile, carbon-rich asteroids helps us address important questions in astrobiology – for example, the possibility that rocky planets such as rocky planets could access a source of vital raw materials,” he said.

To date the carbonates in the Ryugu samples, the team extended the methodology developed at UCLA for a different “short-lived” radioactive decay system involving the manganese isotope 53, which was present in Ryugu.

The study was co-led by Caitlin McCain, a UCLA doctoral student at the time of the research who is now working at NASA’s Johnson Space Center in Houston, and postdoctoral researcher Nozomi Matsuda, who works in the Ionic Microbe Laboratory in the UCLA Department of Earth. and planetary and space sciences.

Other co-authors of the paper are scientists from the Kochi Phase II team in Japan, led by Moto Ito. This team is responsible for curating particles from the regolith sample collected from the asteroid Ryugu and analyzing their petrochemical and chemical properties through coordinated microanalysis techniques.

more information:
Kaitlyn A. McCain et al, Early fluid activity on Ryugu inferred by isotopic analyzes of carbonates and magnetite, natural astronomy (2023). DOI: 10.1038/s41550-022-01863-0

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