(248370) 2005 QN137 is the eighth main-belt asteroid, out of more than half a million asteroids in the main belt, confirmed to not only be active, but to have been active on more than one occasion.
These images show the main-belt comet (248370) 2005 QN137. Image credit: Hsieh et al., arXiv: 109.14822.
(248370) 2005 QN173 was discovered to be active on July 7, 2021 in data obtained by the Asteroid Terrestrial-Impact Last Alert System (ATLAS) survey telescope.
On that date, the object was at a heliocentric distance of 2.39 AU (astronomical units), and exhibited a thin, straight dust tail.
“This behavior strongly indicates that its activity is due to the sublimation of icy material,” said Dr. Henry Hsieh, senior scientist at the Planetary Science Institute.
“As such, it is considered a so-called main-belt comet, and is one of just about 20 objects that have currently been confirmed or are suspected to be main-belt comets, including some that have only been observed to be active once so far.”
“2005 QN173 can be thought of as both an asteroid and a comet, or more specifically, a main-belt asteroid that has just recently been recognized to also be a comet.”
“It fits the physical definitions of a comet, in that it is likely icy and is ejecting dust into space, even though it also has the orbit of an asteroid.”
“This duality and blurring of the boundary between what were previously thought to be two completely separate 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). In July 2021, its tail was more than 720,000 km (450,000 miles) long and 1,400 km (900 miles) wide.
“This extremely narrow tail tells us that dust particles are barely floating off of the nucleus at extremely slow speeds and that the flow of gas escaping from the comet that normally lifts dust off into space from a comet is extremely weak,” Dr. Hsieh said.
“Such slow speeds would normally make it difficult for dust to escape from the gravity of the nucleus itself, so this suggests that something else might be helping the dust to escape.”
“For example, the nucleus might be spinning fast enough that it’s helping to fling dust off into space that has been partially lifted by escaping gas.”
“Further observations will be needed to confirm the rotation speed of the nucleus though.”
Henry H. Hsieh et al. 2021. Physical Characterization of Main-Belt Comet (248370) 2005 QN173. ApJL, in press; arXiv: 109.14822