- Our solar system contains zones or belts of rocky and icy debris. Asteroids and comets can be found in such places. And now astronomers are finding belts of material around other stars, too.
- Now, they have imaged 74 belts around nearby stars, the largest number they’ve obtained so far. These belts are relatively far from their stars and so contain icy debris, the raw materials for comets.
- So these newly found belt are being called “exocomet belts.” They vary widely in both appearance and age. Some are still young, while others are older and more like those in our own solar system.
Exocomet belts around 74 nearby stars
Our solar system contains regions of icy and rocky debris known as belts. Many asteroids and comets reside in or originate from these belts. For the first time, astronomers have imaged 74 of these so-called exocomet belts around nearby stars in a new survey called REASONS. Researchers from Trinity College Dublin in Ireland led the new international study and said on January 17, 2025, that the images show light being emitted from 74 exocomet belts and the tiny icy or rocky pebbles in them. The study used data from both the Atacama Large Millimeter/submillimeter Array (ALMA) in the Atacama Desert in Chile, and the Submillimeter Array (SMA) in Hawaii.
The researchers published their peer-reviewed study in Astronomy and Astrophysics on January 17, 2025.
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Exocomet belts around 74 nearby stars
The survey, called REASONS (REsolved ALMA and SMA Observations of Nearby Stars), imaged 74 nearby stars of various ages. Any comets, asteroids or other debris are of course way too tiny to be seen themselves. But astronomers can image the comet belts overall around their stars. The new images go beyond what previous observations could achieve, revealing the locations of the pebbles.
How does REASONS do this? The two telescope arrays observe electromagnetic radiation at millimeter and submillimeter wavelengths. The belts of comets show up brightly in those images. Lead author Luca Matrà at Trinity College Dublin said:
Exocomets are boulders of rock and ice, at least 1 km (.6 mile) in size, which smash together within these belts to produce the pebbles that we observe here with the ALMA and SMA arrays of telescopes. Exocometary belts are found in at least 20% of planetary systems, including our own solar system.
The Kuiper Belt is a good example of a similar belt in our own solar system. Astronomers think there are millions of small, icy objects in this region, including hundreds of thousands that are larger than 60 miles (100 km) wide. Some of the objects, including Pluto, are over 600 miles (1,000 kilometers) wide. It is one of the primary sources of comets.
Remarkable diversity of exocomet belts
The images revealed a wide array of comet belts. As co-author Sebastián Marino at the University of Exeter noted:
The images reveal a remarkable diversity in the structure of belts. Some are narrow rings, as in the canonical picture of a ‘belt’ like our solar system’s Edgeworth-Kuiper belt. But a larger number of them are wide, and probably better described as ‘disks’ rather than rings.
Hints of planets
Some of the stars even have multiple belts. This could indicate that planets exist or are forming. The gravity of the planets could help shape the rings and disks by “shepherding” material. We see a similar process in Saturn’s rings, where tiny moonlets help the rings keep their shapes.
Properties and trends
The images are also helping astronomers see overall properties and trends in the exocomet belts. Plus there might even be moon-sized bodies within the belts themselves. Matrà said:
The power of a large study like REASONS is in revealing population-wide properties and trends. For example, it confirmed that the number of pebbles decreases for older planetary systems as belts run out of larger exocomets smashing together, but showed for the first time that this decrease in pebbles is faster if the belt is closer to the central star. It also indirectly showed – through the belts’ vertical thickness – that unobservable objects as large as 140 km (87 miles) to moon-size are likely present in these belts.
Future studies
The REASONS study also lays the groundwork for additional future studies, to help astronomers learn more about the exocomet belts. Astronomer David Wilner at the Center for Astrophysics | Harvard & Smithsonian in Cambridge, Massachusetts, added:
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. The REASONS survey required a large community effort and has an incredible legacy value, with multiple potential pathways for future investigation.
For example, 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, from JWST to the next generation of Extremely Large Telescopes and ALMA’s upcoming ARKS Large Program to zoom even further onto the details of these belts.
Bottom line: The new REASONS survey has found exocomet belts around 74 nearby stars. The images reveal a wide variety of comet belt appearances and ages.
Source: REsolved ALMA and SMA Observations of Nearby Stars (REASONS)
Via Trinity College Dublin
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