In 2021, a celestial body in the asteroid belt was confirmed to be a main belt comet, characterized by its icy composition and near-Sun comet behavior. The researchers emphasize the importance of these findings for understanding the distribution of ice in the interior of the Solar System.

Discovery of a new main belt comet

In 2021, scientists discovered a mysterious object in the main asteroid belt. It has now been identified as a main belt comet by Henry Hsieh of the Planetary Science Institute, Scott Sheppard of the Carnegie Institution for Science, and Audrey Thirouen of the Lowell Observatory.

Main belt comets are icy objects found in the asteroid belt between Mars and Jupiter. This is a surprising location since icy bodies are often found in the cold outer regions of the solar system. These comets have distinctive features, such as tails from the Sun or cloudy clouds formed when the Sun’s heat evaporates their ice. The first main belt comets were discovered in 2006 by Hsieh and his colleague Dr. from the University of Hawaii. Determined by David Jewitt.

Characteristics and observation methods

Main belt comets belong to a larger group of Solar System objects called active asteroids, which are similar to comets but move in asteroid orbits in the warmer interior of the Solar System. Active asteroids include not only objects exhibiting cometary behavior resulting from the evaporation of ice, but also objects whose dust clouds and tails form as a result of impact or rapid rotation. Although main belt comets and active asteroids remain relatively rare, scientists are discovering them more frequently as observation techniques improve.

Xie and colleagues observed active asteroid 456P/PANSTARRS twice with the Magellan Baade Telescope and the Lowell Discovery Telescope in October 2024 to determine its status as the 14th confirmed main belt comet. They published their findings Research Notes of the American Astronomical Society.

Description of comet-like activity

“This object is not only an asteroid that experienced a one-time event that activated it, but also an inherently active, icy body similar to other comets in the outer solar system,” Xie said.

If 456P/PANSTARRS’s activity was caused by something other than ice evaporation, its tail should only appear randomly once near the Sun, rather than repeatedly. On the other hand, whenever an icy object approaches the Sun, it heats up and the evaporating ice drags dust with it. Activity ceases when the object moves away from the Sun and cools.

The importance of continuing research

Observation of repeated dust ejection activity during close approaches to the Sun is currently considered the best and most reliable way to identify main belt comets.

“Very few confirmed main belt comets are known so far,” Xie said. “We want to establish a population so that we can get a clearer picture of their size, activity period and broader characteristics, such as their distribution in the asteroid belt, so that they can be better used to track ice in the solar system in general”.