Remember 'Oumuamua? The 'Interstellar Visitor' Is Probably A Comet After All, Researchers Say

The solar system's first ever interstellar visitor 'Oumuamua turns out to be just another comet after all, albeit a strange one.

Since it was first spotted in 2017, scientists have been wondering what the mysterious interstellar space rock is: a comet, an asteroid, or perhaps even something else entirely.

Now, a new study published in the journal Nature confirms that 'Oumuamua is indeed a comet, despite the distinct lack of a tail.

'Oumuamua Is A True Comet, Scientists Report

As it hurtled farther and farther away, astronomers all over the world tracked it for as far and as long as they could, but it soon disappeared out of sight.

Some initially categorized it as an asteroid, which is primarily made of rock and metal. Further observations reveal that it's actually a comet, which is made of ice, dust, and rock.

Scientists saw that there was a force constantly tugging the rock further away from the sun. However, it was also apparent that this force and the movement of 'Oumuamua could not be explained by the gravitational pull of the sun, the planets, or other major celestial bodies in the solar system.

"As it moved away from the Sun, it was slowing down a little bit less than we would have expected," Karen Meech, an astronomer at the University of Hawaii, explains in the statement.

Instead, the researchers concluded that outgassing is the most likely explanation for the mysterious space rock's behavior. 'Oumuamua flew close to the sun, growing warmer and melting the ice at its core. The gas that resulted from this shot outward, giving the space rock just a little more push.

Outgassing is a common behavior of comets, but 'Oumuamua reportedly has a relatively small rate. This weak outgassing and its large dust particles are why the interstellar visitor never developed a tail that other comets have.

The First Ever Interstellar Comet

In October 2017, astronomers spotted the 'Oumuamua with the PanSTARRS-1 telescope in Maui, Hawaii. The trajectory indicated that it's different from other known celestial objects, which told the scientists the mystery object could have come from outside the solar system.

This is a notable event, since this is the first interstellar object ever detected on Earth. 'Oumuamua's Hawaiian name reflects its origins, translating to "a messenger from afar arriving first."

The scientists didn't get much time to observe the visitor, though, since 'Oumuamua was already flying past the sun and on its way out of the solar system by the time it was spotted.