Astrophysicists have taken images of a large sample of exocomet belts for the first time, imaging the bands along with the tiny pebbles that orbit within. The images were published in a study in Astronomy and Astrophysics, showing bands of a variety of structures.

“The images reveal a remarkable diversity in the structure of belts,” said Sebastián Marino, a study author and an astronomer at the University of Exeter, according to a press release. “Some are narrow rings […] but a larger number of them are wide, and probably better described as ‘disks’ rather than rings.”

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Exploring Exocomet Belts

In our own Solar System, comet belts are bands of comets and other objects that orbit the Sun. The Kuiper Belt is one such band, orbiting the Sun beyond the reach of Neptune. Formed from the remnants of the birth of the Solar System, the Kuiper Belt is basically a band of frozen leftovers.

But the Kuiper Belt isn’t the only band of frozen leftovers out there. Similar bands surround other stars, too, in solar systems other than our own. These exocomet belts are a lot like the comet belts in our own Solar System, featuring exocomets and other objects, frozen at temperatures of around negative 420 degrees Fahrenheit to negative 240 degrees Fahrenheit.

“Exocometary belts are found in at least 20 percent of planetary systems,” said Luca Matrà, another study author and an astrophysicist at Trinity College Dublin, according to the release.

Surprising Sizes

Setting out to survey a large sample of exocomet belts for the first time — and dubbing the survey REASONS (REsolved ALMA and SMA Observations of Nearby Stars) — a team of astrophysicists imaged 74 exocomet belts of various structures. Some were narrower, some were broader, and some weren’t alone, belonging to systems with multiple bands.

“The power of a large study like REASONS is in revealing population-wide properties and trends,” said Matrà in the release.

One of these trends, for instance, related to the broadness of the belts, which tended to be wide, not narrow like our own Kuiper Belt. Another related to the objects inside the belts: Older belts tended to contain fewer pebbles, which form when exocomets collide.

“Exocomets are boulders of rock and ice […] which smash together within these belts to produce the pebbles that we observe here,” said Matrà in the release. “The number of pebbles decreases for older planetary systems as belts run out of larger exocomets smashing together. […] This decrease in pebbles is faster if the belt is closer to the central star.”

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A Telescopic Team

To image these exocomets, which also varied in age from young to old, the team turned to the ALMA and SMA telescope arrays.

Comprising 66 radio telescopes in the Atacama Desert in Chile and 8 radio telescopes on Maunakea in Hawaii, the Atacama Large Millimeter/Submillimeter Array (ALMA) and the Submillimeter Array (SMA) were capable of capturing these exocomet belts in crystal-clear resolution, revealing their impressive range of sizes.

“Arrays like the ALMA and SMA used in this work are extraordinary tools that are continuing to give us incredible new insights into the universe and its workings,” said David Wilner, another study author and an astrophysicist at the Center for Astrophysics | Harvard & Smithsonian, in the release. “The REASONS survey required a large community effort and has an incredible legacy value, with multiple potential pathways for future investigation.”

New insights could come from the same telescopes, or from others, like the James Webb Space Telescope.

“The REASONS dataset of belt and planetary system properties will enable studies of the birth and evolution of these belts, as well as follow-up observations across the wavelength range,” said Wilner in the release, “to zoom even further onto the details of these belts.”

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Sam Walters is a journalist covering archaeology, paleontology, ecology, and evolution for Discover, along with an assortment of other topics. Before joining the Discover team as an assistant editor in 2022, Sam studied journalism at Northwestern University in Evanston, Illinois.