Astronomers were left surprised when they found a rare comet/asteroid hybrid in the asteroid belt between Mars and Jupiter. Named 2005 QN173, it has traits of both a comet and an asteroid.
2005 QN173 orbits in the same way as any other asteroid – it travels around the sun in the outer part of the asteroid belt, making a full circle about every 5 years. However, based on data collected on July 7th by the Asteroid Terrestrial-Impact Last Alert System (ATLAS) survey in Hawaii, astronomers realized that it had a long thin tail. This indicates that it is full of icy material that is vaporizing in space during its journey. Interestingly, when they searched through data from the Dark Energy Camera when 2005 QN173 orbited the sun in 2016, they noticed that it also had a tail at that time.
In a statement, Henry Hsieh, who is a planetary scientist at the Planetary Science Institute, explained these unusual differences in further detail, “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”
Scientists have already studied about half a million space objects in the asteroid belt and incredibly, 2005 QN173 is only the eighth of its kind to have been active on multiple occasions. Furthermore, it is only one of 20 objects that have been categorized as being “main-belt comets.”
Some other interesting facts about 2005 QN173 was that when it was analyzed between 2004 and 2020, there were several times that it wasn’t active so the researchers had a better opportunity to study it and they found that its nucleus (or head) was approximately 2 miles wide (3.2 kilometers). New observations conducted this summer revealed more details regarding its exceptionally long tail that measures 450,000 miles (724,000 kilometers). For comparison, it is almost twice the distance of Earth to our moon.
And if that’s not confusing enough, its tail isn’t very wide as detailed by Hsieh, “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.” “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.” Perhaps the nucleus may be spinning so fast that it is spewing out extra dust, but that’s just a theory for now.
Whatever this crazy mysterious space object is, scientists will be waiting for February 2026 when they will hopefully get a better understanding of it when its location to the sun may possibly reactive it. A composite image that shows 2005 QN173’s nucleus and its long tail can be seen here.
Their research can be read in full here.