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Thursday, June 13, 2024 | Back issues
Courthouse News Service Courthouse News Service

Astronomers detect evidence of possible asteroid collisions in ‘teenage’ solar system

The findings could help scientists better understand how rocky planets form, and how common solar systems with rocky planets may or may not be.

(CN) — Astronomers with John Hopkins University announced Monday that they had detected what could be asteroid collisions in a nearby young star system.

The lead scientist on the study, John Hopkins astronomer Christine Chen, said she and her team made the discovery "serendipitously." Chen first studied dust clouds in the Beta Pictoris star system, some 63 light years away, using the Spitzer Space Telescope in 2004 and 2005. When she and her team took another look at the system last year using the James Webb Space Telescope's infrared cameras, what stood out was what wasn't there.

"One of the big surprises that we had when our data came down in January 2023 was that two of the dust components that we had seen in the Spitzer data from 2004 to 2005, had disappeared," Chen said Monday while presenting her team's findings at a meeting of the American Astronomical Society in Madison, Wisconsin.

The disappearance of the previously-observed dust clouds, Chen said, led researchers to believe they were witnessing the aftermath of a large collision. The Beta Pictoris solar system is young, the astronomer explained, but not so young that its protoplanetary disc — the material from which planets and other bodies form — was still only composed of loose gas and dust. She instead described it as a "teenage" solar system that was home to larger bodies, including at least two giant planets several times larger than Jupiter.

"It's partially formed its planetary system but it's not done yet," Chen said. "There's... exocomets and asteroids and they're banging into each other and by those processes forming terrestrial planets and also creating dust debris," she added.

As material from the protoplanetary disc clumps together to form comets, asteroids and planets, violent collisions between these objects could become more common. The researchers believe such a collision created the dust clouds — largely composed of a mineral called forsterite — Chen observed in 2004 and 2005. Stellar radiation could then have blown away many of the smaller dust grains, perhaps finer than powdered sugar, explaining their absence in 2023.

The differences in dust clouds in the Beta Pictoris star system, observed with two different telescopes 20 years apart, suggest we're looking at the aftermath of a violent asteroid collision. (Roberto Molar Candanosa / Johns Hopkins University, Beta Pictoris concept art by Lynette Cook/NASA)

The findings suggest that Beta Pictoris is a chaotic place at the moment. Other evidence also exists to support this hypothesis, such as the 2014 discovery of carbon monoxide gas in the system.

Carbon monoxide is a relatively fragile gas that can only last about a century in space before starlight destroys it. As Beta Pictoris is about 20 million years old already, any carbon monoxide in the system must be newly created.

"A plausible explanation is the collisions between icy planetesimals in the outer part of that planetary system liberating the carbon monoxide gas," Chen said.

Besides giving scientists greater insight into what Chen called the "collisionally active" nature of Beta Pictoris specifically, the findings announced Monday could help scientists better understand how rocky planets form in general. Another scientist who spoke in Madison on Monday, Lisa Prato of Arizona's Lowell Observatory, said there are still many unanswered questions regarding planet formation in general.

Prato explained that the "primordial" discs of gas and dust leftover from a star's birth only last for about the first 10 million years of a solar system's lifetime. But her own research suggested that large gas planets may form earlier within these discs — and closer to their parent star — than previously thought.

"That's exactly what I'm trying to get at ... is to understand how long it takes to form observable planets and are they already forming much earlier than we anticipated," Prato said.

Chen clarified that compared to the primordial discs Prato studied, the debris discs that form rocky planets have much less gas and are generally made of younger material; what she called "second generation." In our own solar system, for example, the rocky planets may have congealed when the system was around 200 million years old, whereas Jupiter may have formed when the solar system was only 5 to 10 million years old.

"That initial disc forms out of gas and dust from the interstellar medium. When you get to the debris disc stage, all that material inherited from the interstellar medium has been incorporated into larger bodies," Chen told Courthouse News in an interview.

This implies terrestrial planets are generally formed from a violent series of collisions, rather than the smooth accumulation of surrounding gas and dust. The inner planets of our own solar system bear evidence of this violent past, perhaps not so different from Beta Pictoris' own awkward teenage phase.

"If you look at the surface of Mercury, or the moon or Mars, they're full of craters," Chen said. "That implies there's lots of collisions going on.

“The question we are trying to contextualize is whether this whole process of terrestrial and giant planet formation is common or rare, and the even more basic question: Are planetary systems like the solar system that rare?” Kadin Worthen, a doctoral student in astrophysics at Johns Hopkins, and another co-author of Monday's study, said in a prepared statement.

“We’re basically trying to understand how weird or average we are," she said.

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