Free Astronomy Magazine March-April 2025

T he 74 exocomet belts imaged by ALMA’s REASONS survey show belts of all shapes, sizes and ages. [ALMA (ESO/NAOJ/NRAO)/SMA/L. Matrà et al.] 24 ASTRO PUBLISHING One of the telescopes that can ob- serve them is the Atacama Millime- ter/submillimeter Array (ALMA). This array of 66 antennas in north- ern Chile is specifically designed to detect long wavelength radiation from cold astronomical sources, like exocomet belts. Using ALMA, the Hawaiian Submil- limeter Array (SMA), and archival data, a team led by Luca Matrà, an associate professor at the University of Dublin, has embarked on a mis- sion to image as many exocomet belts as possible in all stages, from newly formed to very mature. The survey, Resolved ALMA and SMA Observations of Nearby Stars (REA- SONS), is the largest of its kind to date. The survey contains images of 74 belts around “nearby” planetary systems located within 500 light- years of Earth. The results, published in Astronomy and Astrophysics , al- ready challenge astronomers’ ideas about these structures. Not all belts are equal. The REASONS survey revealed that exocomet belts come in all shapes, sizes, and ages, but scientists are starting to see some patterns within this variation. One of these patterns is that belts are remarkably larger than ex- pected. Smaller belts are closer to their host star, making them hotter, brighter, and theoretically more