Free Astronomy Magazine March-April 2025

23 MARCH-APRIL 2025 ASTRO PUBLISHING could have prevented dust beyond its orbit from creating new planets, leaving us with just a belt of debris. This debris, though, is a hidden space treasure. Today, the Kuiper Belt is a collection of dusty and icy space rocks, ranging from dust grains and pebbles to comets and dwarf planets. From a few millimeters to kilometers in di- ameter, many of these objects have changed little since their formation. Frozen (literally) in time, these are remnants of the early stages of the Solar System and tell us a lot about its initial properties. Belts of debris like the Kuiper Belt exist in other planetary systems, too. They are broadly known as “planetesimal belts” since the ob- jects within them have the potential to coalesce to form planets, or “ex- ocomet belts” since they usually hide comets (icy planetesimals) within them. But how can we ob- serve these belts? Given their size, finding exocomet belts should be easy at first glance. However, belts have been difficult to observe and image. The reason behind this is their temperature. The objects lying within an exocomet belt are very far from their host star, and thus, they are extremely cold. In the Kuiper belt, temperatures range from -250 to -150 degrees Celsius. At these low temperatures, belts only shine at long wavelengths, making them difficult to observe for most — but not all — telescopes. A rtist’s impression of the Kuiper belt, a disc ful of icy and rocky objects beyond the orbit of Neptune. [ESO/M. Kornmesser]