Astronomers have discovered a new asteroid belt around nearby star Fomalhaut, as well as a strange ring of debris tilted relative to the rest of the system. Their observations may indicate that this well-studied star system is much more complex than we thought.
Andras Gaspar 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 disk 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 it would have a narrow asteroid belt like our own solar system, but it turns out to be very different,” says Gáspár. Our asteroid belt measures about 1.5 astronomical units in diameter – 1 AU is the distance between the Earth and the sun – while the inner Fomalhaut asteroid belt extends about 7 AU from the star to about 80 AU. It’s about 10 times wider than expected.
There also appears to be some sort of intermediate asteroid belt between the inner belt and the outer disk, but it is tilted about 23 degrees to the plane of the other two belts. This dense band of debris solves a long-standing mystery about Fomalhaut – the source of the material that makes up its famous dust cloud, Fomalhaut b. It was once thought to be a planet, but is now considered likely to be a remnant of two crashed protoplanets.
“One of the criticisms of the Fomalhaut b models being the result of a large collision was the idea that there was no matter inside these Kuiper belt-like rings, and these new observations show that yes, there are, especially in the area where Fomalhaut b is believed to have originated,” says Gáspár “These puzzle pieces all fit together very well.”
In addition to solving the Fomalhaut b problem, the researchers also spotted what appears to be a second huge debris cloud, about 10 times larger than Fomalhaut b, in the outer ring. They called it the Great Dust Cloud, and they think it might have come from another protoplanetary crash.
The spaces between the discs suggest that there could be three or more full-fledged planets, possibly the size of Uranus or Neptune, orbiting Fomalhaut. Researchers are now working on analyzing JWST observations that have taken a closer look, specifically looking for planets.