Webb telescope reveals inner structure of first asteroid belt found beyond our solar system

These belts are thought to be formed by the debris from collisions of larger bodies, like asteroids, and comets.
Mrigakshi Dixit
Image of the dusty debris disk surrounding the young star Fomalhaut is from Webb’s Mid-Infrared Instrument (MIRI)
Image of the dusty debris disk surrounding the young star Fomalhaut is from Webb’s Mid-Infrared Instrument (MIRI)

NASA, ESA, CSA, A. Gáspár (University of Arizona), A. Pagan (STScI) 

Astronomers used the powerful James Webb Space Telescope to closely image the first asteroid belt discovered beyond our solar system, which surrounds a nearby young, hot star called Fomalhaut. 

The dusty belts encircle Fomalhaut, which can be seen as the brightest star in the southern constellation Piscis Austrinus.

The ring structure that surrounds Fomalhaut was discovered in 1983 by NASA's Infrared Astronomical Satellite (IRAS). Since then, astronomers have attempted to study this ring system using various ground and space-based telescopes, including Hubble and Spitzer Space Telescope, and Mauna Kea observatory in Hawaii. These facilities were able to obtain sharp images of the outermost ring, but studying the complex innermost rings was difficult. 

Using its infrared seeing capabilities, Webb was able to reveal the structure of two inner belts in unprecedented detail for the first time. “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,” said Schuyler Wolff, one of the study authors, in an official statement

The complex rings structure

According to NASA, these dusty structures are much more complex than our solar system's main asteroid belt (between Jupiter and Mars) and Kuiper belts (rocks and dust found beyond Neptune).

These three dusty belts span 14 billion miles (23 billion kilometers) from the star. Meanwhile, the outermost belt is twice the size of our solar system's Kuiper Belt.  

These belts are thought to be formed by the debris from collisions of larger bodies, like asteroids, and comets. It is referred to as the debris disk, which is formed usually when the planets are in place. They could have been formed by the gravitational tug of the unseen planets in this star system. The debris belts consist of rocky, icy, and dusty remnants from the massive planetary collision. 

“By looking at the patterns in these rings, we can actually start to make a little sketch of what a planetary system ought to look like – If we could actually take a deep enough picture to see the suspected planets,” said András Gáspár of the University of Arizona in Tucson and lead author of the new paper. 

Mysterious unseen planets

Astronomers regard the belts surrounding the young star as a missing puzzle because no planets have been discovered in the system, despite noticing a mysterious gap between Fomalhaut's outer and inner rings. This new gap could indicate the presence of an unknown ice-giant planet, such as Neptune or Uranus.

Webb also observed "the great dust cloud," which could be interpreted as the collision of two protoplanetary bodies in the outer ring. 

"We definitely didn't expect the more complex structure with the second intermediate belt and then the broader asteroid belt," Wolff said. "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!'"

The team hopes to use JWST to study and image more debris disks around other stars in the future.

“With Hubble and ALMA, we were able to image a bunch of Kuiper Belt analogs, and we've learned loads about how outer disks form and evolve. But we need Webb to allow us to image a dozen or so asteroid belts elsewhere. We can learn just as much about the inner warm regions of these disks as Hubble and ALMA taught us about the colder outer regions,” said Wolff.

The study has been published in the journal Nature Astronomy.

Study Abstract:

Planetary debris disks around other stars are analogous to the asteroid and Kuiper belts in the Solar System. Their structure reveals the configuration of small bodies and provides hints for the presence of planets. The nearby star Fomalhaut hosts one of the most prominent debris disks, resolved by the Hubble Space Telescope, Spitzer, Herschel and the Atacama Large Millimeter Array. Images of this system at mid-infrared wavelengths using JWST/MIRI not only show the narrow Kuiper belt-analogue outer ring, but also that (1) what was thought from indirect evidence to be an asteroid-analogue structure is instead broad, extending outward into the outer system, and (2) there is an intermediate belt, probably shepherded by an unseen planet. The newly discovered belt is demarcated by an inner gap, located at ~78 au, and it is misaligned relative to the outer belt. The previously known collisionally generated dust cloud, Fomalhaut b, could have originated from this belt, suggesting increased dynamical stirring and collision rates there. We also discovered a large dust cloud within the outer ring, possible evidence of another dust-creating collision. Taken together with previous observations, Fomalhaut appears to be the site of a complex and possibly dynamically active planetary system.

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