Absolutely enormous asteroid belt discovered around a nearby star

Astronomers used the James Webb Space Telescope to spot strange asteroid belts around the nearby star Fomalhaut, along with evidence for at least three planets.

Astronomers have discovered a new asteroid belt around the nearby star Fomalhaut, as well as a strange ring of debris that is tilted with respect to the rest of the system. Their observations may indicate that this well-studied star system is far more complex than we thought.

Fomalhaut, a star 25 light years away, hosts an extremely wide asteroid belt and another ring of debris
Adam Block

András Gáspár at the University of Arizona and his colleagues observed Fomalhaut using the James Webb Space Telescope (JWST) and the Hubble Space Telescope. We already knew that Fomalhaut had a huge outer disc of rocks and dust, similar to our solar system’s Kuiper belt, but the predicted inner asteroid belt had never been directly observed before.

“We thought that it would have a narrow asteroid belt like our own solar system, but it turns out it’s very different,” says Gáspár. Our asteroid belt is about 1.5 astronomical units across – 1 AU is the distance between Earth and the sun – while Fomalhaut’s inner asteroid belt stretches from about 7 AU from the star to about 80 AU out. That is about 10 times broader than expected.

There also appears to be a sort of intermediate asteroid belt between the inner belt and the outer disc, but it is tilted by about 23 degrees from the plane of the other two belts. This dense strip of debris solves a long-held mystery about Fomalhaut – the source of the material that makes up its famous dust cloud, Fomalhaut b. This was once thought to be a planet but is now considered most likely to be a remnant from two protoplanets smashing together.

“One of the critiques of the models of Fomalhaut b being the result of a big collision was the idea that there was no material inside of these Kuiper belt-like rings, and these new observations show that yes, there is, especially at the region where Fomalhaut b supposedly originated from,” says Gáspár. “These puzzle pieces all fit together very nicely.”

On top of solving the Fomalhaut b problem, the researchers also spotted what appears to be a second huge debris cloud, around 10 times bigger than Fomalhaut b, in the outer ring. They named it the Great Dust Cloud, and they think it may have originated from another protoplanetary smash-up.

The gaps between the discs hint that there may be three or more full-fledged planets, possibly around the size of Uranus or Neptune, orbiting Fomalhaut. The researchers are now working on analysing JWST observations that took a closer look, specifically seeking out planets.

Journal reference:

Nature AstronomyDOI: 10.1038/s41550-023-01962-6

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