A long-known celestial body behaving strangely – is an asteroid a comet?

A long-known celestial body suddenly does something unexpected – and this raises questions: Is (248370) 2005 QN173 not an asteroid at all, but a comet?

Tucson/Frankfurt – Asteroids and comets are actually two completely different classes of celestial bodies, which basically have one thing in common: they’re both leftovers from when the solar system was formed. Apart from that, comets are designed like “dirty snowballs”, they are made up of dust and loose rock that are held together by ice. When a comet approaches the Sun, part of the ice sublimates and becomes directly gaseous – a characteristic tail characteristic of comets is created. On the other hand, asteroids are usually rocks that revolve around the sun without developing a tail.

In fact, asteroids and comets exist in astronomy Completely different types of celestial bodies. Every once in a while, researchers discover something that doesn’t seem to fit either category — or both. The latter applies to the celestial body with the encoded designation (248370) 2005 QN173. The orb, discovered in 2005, has long been mistaken for an asteroid. It is located in the asteroid belt (also called the main belt) between Mars and Jupiter and has been inconspicuous for a long time. But now researchers at the Planetary Science Institute (PSI) in Tucson (Arizona) have announced that the asteroid is active, that is, it is spewing gases and has developed a tail. The interview study The publication was accepted by the specialist journal Astrophysical Journal Letters.

Comet or asteroid? Celestial Body (248370) 2005 QN173 seems to be both

“Its behavior strongly suggests that its activity is due to sublimation of icy materials,” explains lead author of the study, Henry Hsieh of PSI. This makes the asteroid a so-called “main belt comet,” Hsieh explained when presenting his study at a virtual meeting of the American Astronomical Society. “It’s one of only about 20 objects that are currently confirmed or suspected to be major belt comets,” Hsieh said. Some of the 20 objects were also observed to be active only once, while the activity was observed several times for the orb (248370) 2005 QN137.

“247370 can be considered asteroids and comets, or more precisely, as a major asteroid in the belt, which has only recently been recognized as a comet,” Hsieh is trying to identify the orb. “It meets the physical definitions of a comet because it is very likely to be icy and blow dust into space, even if it is orbiting around an asteroid,” Hsieh continues. “This duality and the blurring of lines between what were previously thought to be two very different types of objects – asteroids and comets – is a key part of what makes these things so interesting,” Hsieh says.

Main belt comet and asteroid in one: (248370) 2005 QN173 exciting research

Hsieh’s research team found that the comet’s nucleus, surrounded by a cloud of dust, has a diameter of 3.2 kilometers. In July 2021, the comet’s tail was more than 720,000 km long and about 1,400 km wide. The very narrow tail shows that dust particles are moving away from the core at very low speeds and that the comet’s gas flow is very weak. This, in turn, suggests that something else is helping the dust escape from the comet’s nucleus — the core might spin quickly and throw dust into space. However, more observations are needed to confirm this, Hsieh says.

PSI researcher Hsieh and colleague David Jewett were the first to discover a new class of main belt comets in 2006. Rare main belt comets are particularly exciting to research: There is a theory that asteroid collisions once brought a significant portion of the water to Earth. Since the comets’ outgassing in the main belt likely means they still contain water, they may be worthwhile targets for future exploration. (tab)