A mysterious object discovered in the main asteroid belt in 2021 was determined to be a main-belt comet by Planetary Science Institute Senior Scientist Henry Hsieh, Scott Sheppard of the Carnegie Institution for Science and Audrey Thirouin of Lowell Observatory.
Main-belt comets are icy objects found in the asteroid belt between Mars and Jupiter—rather than the cold outer solar system where icy bodies are typically expected. They sport comet-like features, like tails extending away from the sun or fuzzy clouds as the sun’s heat vaporizes their ice. They were first discovered in 2006 at the University of Hawaii by Hsieh and his then-doctoral advisor, David Jewitt.
Main-belt comets belong to a larger group of solar system objects known as active asteroids, which look like comets, but have asteroid-like orbits in the warm inner solar system. This larger group includes objects whose clouds and tails are made of ejected dust produced after an impact or as they quickly rotate, rather than just those that eject dust due to vaporized ice. Both main-belt comets and active asteroids in general are still relatively rare, but scientists are discovering them at a growing clip.
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