Recently-Discovered Active Asteroid is in Fact Main-Belt Comet, Astronomers Say | Sci.News
456P/PANSTARRS, an active, main-belt asteroid first spotted in 2021, is recurrently active, and activity is likely driven by the sublimation of volatile ice, according to new observations from the Magellan-Baade telescope and the Lowell Discovery Telescope.
Images of 456P/PANSTARRS taken with the Magellan-Baade telescope in Chile on October 3, 2024, and the Lowell Discovery Telescope in Arizona on October 26, 2024, where the head, or nucleus, of the comet is at the center of each image, and the tail extends to the right. Image credit: Scott S. Sheppard / Carnegie Institution for Science / Audrey Thirouin, Lowell Observatory / Henry H. Hsieh, Planetary Science Institute.
“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,” said Planetary Science Institute senior scientist Henry Hsieh and colleagues.
“They sport comet-like features, like tails extending away from the Sun or fuzzy clouds as the Sun’s heat vaporizes their ice.”
These objects were first discovered in 2006 at the University of Hawaii by Dr. Hsieh and his then-doctoral advisor, Professor 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,” the astronomers said.
“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.”
456P/PANSTARRS was discovered as P/2021 L4 (PANSTARRS) from observations on June 9 and 14, 2021, by Pan-STARRS1, and Canada-France-Hawaii Telescope observations on June 14, 2021.
Dr. Hsieh and co-authors observed the object twice using the Magellan Baade Telescope and Lowell Discovery Telescope in October 2024 to establish its status as a main-belt comet.
“This object is not just an asteroid that experienced a one-off event that caused it to show activity one time, but is an inherently active, icy body similar to other comets from the outer Solar System,” Dr. Hsieh said.
If 456P/PANSTARRS’s activity were due to something other than ice vaporization, then its tail would be expected to appear only once randomly, and not repeatedly appear when it was close to the Sun.
An icy object, on the other hand, heats up every time it approaches the Sun, and the vaporized ice drags dust out along with it.
When the object moves farther from the Sun and cools, the activity stops.
Observations of repeated dust ejection activity during close approaches to the Sun are currently considered the best and most reliable way to identify main-belt comets.
“There are still very few confirmed main-belt comets known,” Dr. Hsieh said.
“We want to build up the population so we can get a clearer idea of what their broader properties are — such as their sizes, activity duration and distribution within the asteroid belt, for example — so that they can be better used to trace ice in the Solar System in general.”
The findings were published in the Research Notes of the American Astronomical Society.
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Henry H. Hsieh et al. 2024. Confirmation of Recurrent Activity of Main-Belt Comet 456P/PANSTARRS (P/2021 L4). Res. Notes AAS 8, 283; doi: 10.3847/2515-5172/ad90a6
This article is a version of a press-release provided by the Planetary Science Institute.
