How did the solar system form? The Ryugu asteroid is helping us learn

Mineral samples collected from the Ryugu asteroid by the Japanese Hayabusa2 spacecraft are helping UCLA space scientists and colleagues 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 nature astronomyscientists who use isotope analysis he discovered that carbonate minerals from the asteroid crystallized through reactions with water, which originally accumulated on the asteroid as ice in the still-forming solar system, and then heated to a liquid. These carbonates, they say, formed very early, within 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 aqueous fluid as it existed at the time.

The rocky, carbon-rich Ryugu is the first C-type asteroid (C stands for “carbonaceous”) to have samples collected and studied, said study co-author Kevin McKeegan, distinguished professor of Earth, planetary and space sciences at the UCLA. What makes Ryugu special, he pointed out, is that, unlike meteorites, it hasn’t had potentially contaminating contact with Earth. By analyzing the chemical fingerprints in the samples, scientists can develop a picture of not only how Ryugu formed but also where.

“The Ryugu samples tell us that the asteroid and similar objects formed relatively quickly in the outer solar system, beyond the water ice and carbon dioxide condensation fronts, probably as small bodies,” McKeegan said.

The researchers’ analysis determined that the Ryugu carbonates formed several million years earlier than previously thought, and indicate that Ryugu, or a parent asteroid from which it may have broken off, accreted as a relatively small object, probably less than 20 kilometers (12.5 miles). ) in diameter.

This result is surprising, McKeegan said, because most asteroid accretion models would predict assembly over longer periods, resulting in the formation of bodies at least 50 kilometers (more than 30 miles) in diameter that could better survive collisional evolution throughout the long history of the solar system.

And although Ryugu is currently only about 1 kilometer in diameter as a result of collisions and reassembly throughout its history, it is highly unlikely that it was ever a large asteroid, the researchers said. They noted that any larger asteroid formed very early in the solar system would have been heated to high temperatures by the decay of large amounts of aluminum-26, a radioactive nuclide, resulting in melting of rock throughout the interior of the asteroid, along with chemicals. differentiation, such as the segregation of metal and silicate.

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.

McKeegan said that ongoing research on the Ryugu materials will continue to open a window into the formation of the planets in the solar system, including Earth.

“Improving our understanding of carbon-rich and volatile asteroids helps us address important questions in astrobiology, for example, the likelihood that rocky planets could access a source of prebiotic materials,” he said.

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

The study was co-led by Kaitlyn McCain, a UCLA doctoral student at the time of the research who now works at NASA Johnson Space Center in Houston, and postdoctoral researcher Nozomi Matsuda, who works in the Ion Microprobe Laboratory at NASA. UCLA Land Department. , Planetary and Space Sciences.

Other co-authors on the paper are scientists from the Kochi Phase 2 healing team in Japan, led by Motoo Ito. This team is responsible for curing particles from the regolith sample collected from the Ryugu asteroid and analyzing their chemical and petrological characteristics using coordinated microanalytical techniques.