Astronomers spot comet in solar system’s main asteroid belt

(248370) 2005 QN137 is the eighth asteroid in the main belt, out of more than half a million asteroids in the main belt, confirmed not only to be active, but to have been active on more than one occasion.

These images show the 2005 Main Belt Comet (248370) QN137. Image credit: Hsieh et al., arXiv: 109.14822.

(248370) 2005 QN173 was found active on July 7, 2021 in data obtained by the Land Asteroid Impact Alert System (ATLAS) Study Telescope.

At this date, the object was at a heliocentric distance of 2.39 AU (astronomical units), and exhibited a thin straight dust tail.

“This behavior is a strong indication that its activity is due to the sublimation of icy matter,” said Dr. Henry Hsieh, senior scientist at the Planetary Science Institute.

As such, it is considered a main belt comet and is among 20 objects currently confirmed or suspected to be main belt comets, some of which have only been observed active once. until there.”

“2005 QN173 can be thought of as both an asteroid and a comet, or more precisely, a main belt asteroid that has just been recognized as a comet as well.”

“This fits the physical definitions of a comet, in that it is probably icy and throws dust into space, even though it also has the orbit of an asteroid.”

“This duality and blurring of the line between what were previously thought to be two completely distinct types of objects – asteroids and comets – is a key part of what makes these objects so interesting.”

2005 QN173 has a diameter of 3.6 km (2 miles). As of July 2021, its tail was over 720,000 km (450,000 miles) long and 1,400 km (900 miles) wide.

“This extremely narrow tail tells us that dust particles barely float out of the nucleus at extremely slow speeds, and that the flow of gas escaping from the comet that normally lifts dust from a comet into space is extremely low, ”said Dr. Hsieh. .

“Such slow speeds would normally make it difficult for dust to escape from the gravity of the core itself, so this suggests that something else might be helping the dust to escape.”

“For example, the core can spin fast enough to help project dust into space that has been partially lifted up by the escaping gas.”

“However, further observations will be needed to confirm the rotational speed of the nucleus.”

The team’s article was published in the Letters from astrophysical journals.


Henry H. Hsieh et al. 2021. Physical characterization of the main belt comet (248370) 2005 QN173. ApJL, in the press; arXiv: 109.14822

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