Star Fomalhaut has dusty little secret – two more debris belts and a potential planetary party

Nearby system was thought to have an exoplanet, but that was wrong. Now NASA says there may be multiple

The James Webb Space Telescope is stirring up more space mysteries with the discovery of an additional pair of debris belts around a young nearby star long believed to have only one.

As opposed to having just one dusty ring roughly twice the size of the solar system's Kuiper Belt around it, JWST used the Mid-Infrared Instrument, or MIRI, to spot two more dust belts nestled within the outer belt surrounding the star Fomalhaut. As there are gaps in the disks, NASA scientists believe that, despite previous disappointments in that very star system, there are likely several undiscovered exoplanets orbiting the nearby star.

"We definitely didn't expect the more complex structure with the second intermediate belt and then the broader asteroid belt," said project astronomer Schuyler Wolff from the University of Arizona's Steward Observatory. "That structure is very exciting because any time an astronomer sees a gap and rings in a disk, they say, 'There could be an embedded planet shaping the rings!'"

Fomalhaut, which is a mere 25 light years from Earth and is just 440 million years young, had its first dust ring identified in 1983. It took the new JWST to finally detect the inner pair of rings, which even eluded Hubble and the Atacama Large Millimeter Array, both of which have made multiple observations of the Fomalhaut system.

"Where Webb really excels is that we're able to physically resolve the thermal glow from dust in those inner regions. So you can see inner belts that we could never see before," Wolff said.

The hunt for Fomalhaut's planets is back on

With its gapped trio of debris belts, NASA believes there's likely multiple unseen planets orbiting Fomalhaut as similar corralling of debris happens in our solar system. The inner asteroid belt that orbits between Mars and Jupiter is controlled by the latter of those planets, while Neptune's influence is responsible for shaping the edge of the Kuiper Belt.

Excitement had previously surrounded Fomalhaut in 2008 when Hubble observed what was believed to be a large planet on the inner edge of the star's outer debris belt – the first such potential exoplanet to be directly observed. The "planet" disappeared in 2014, and astronomers now believe what they saw was more likely to be a collision between two planetesimals that has since dispersed. 


The trio of debris belts around Fomalhaut, with detail of a supposed exoplanet (now believed to have been a planetoid collision) at right

Three rings, however, means at least a couple of planets orbiting between them, and possibly another beyond the outer ring. Whether those planets are even done forming, however, is yet another unanswered question.

At a mere 440 million years old (our Sun is around 4.6 billion years old), it's possible that planets could still be coalescing around Fomalhaut, making it an ideal location to focus further research into the birth and formation of planets.

"I think it's not a very big leap to say there's probably a really interesting planetary system around the star," said George Rieke, US science lead for the JWST's MIRI. ®


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