Accelerating the interstellar object – Oumuamua is a comet, not an asteroid

Since Rob Weryk spotted for the first time 'Oumuamua crossing the solar system in October 2017, the particular object has been the target of close scrutiny by world astronomers whole. After confirming that the suspected asteroid reached a maximum speed of nearly 200,000 miles per hour during its closest approach to the Sun (and had the shape of a cigar), the researchers quickly focused on the composition and the origin of this mysterious object.

In a study published in March, astronomers suggested that "Oumuamua may be an asteroid that flew through our solar system after being ejected from a binary star system. Although they rely on models to show that it was a possibility, at the time, the main author Alan Jackson noted: "It's really strange that the first object we will see apart from our system would be an asteroid because a comet would be much easier The solar system ejects many more comets than asteroids. "

Now, by combining the telescopic data from the Hubble Space Telescope and other ground-based observatories, an international team of astronomers has shown that" Oumuamua is indeed a comet -boosted speed rather than a lack of space. 39, an asteroid as astronomers previously thought.

In the new study, published June 27 in the journal Nature the researchers determined that "Oumuamua is accelerating slowly and steadily away from the Sun, which means that he is currently traveling faster than do not predict the celestial mechanics. a branch of astronomy very well understood that deals with the movements of cosmic objects. "Our high-precision measurements of the position of Oumuamua revealed that something was affecting its motion other than the gravitational forces of the Sun and planets," said Marco Micheli, head of the European Space Agency in a statement. NASA release.

Recent observations by "Oumuamua" show that the interstellar object does not follow the well-known laws of celestial mechanics, suggesting that another force is altering its motion across the planet. ;space.

NASA / JPL-Caltech

The researchers explored a number of possible scenarios in order to explain the faster than expected speed with which Oumuamua derives from the solar system. But after considering all the possibilities (such as solar radiation pressure, frictional forces and magnetic interactions with the solar wind), the team concluded that the most likely explanation is that the sun takes Oumuamua out of the gas and dust. surface in a process called degassing, which occurs almost exclusively in icy comets, not rocky asteroids.

This ejection of matter – caused by the evaporation or sublimation by the sun of the trapped gases just below the surface of 'Oumuamua – generates a small push. And although this thrust induced by the release of gas is low, according to the researchers, it is sufficient to take into account the speed increase observed by Oumuamua.

"We think that it is a tiny, strange comet," said lead author Marco Micheli, of the European Space Agency (ESO), in A press release. "We can see from the data that his boost is smaller, the more he travels from the Sun, which is typical for comets."

However, the researchers point out that "Oumuamua does not seem to degas like most other comets found in the solar system. Specifically, when the comets of our solar system are heated by the sun, degassing usually leads to the ejection of material, which forms a hazy cloud around them called a coma, plus a characteristic tail. However, for &umuamua, the researchers found no visual proof of these features.

"We have not seen any dust, coma or tail, which is unusual," said co-author Karen Meech of the University of Hawaii. "We think that" Oumuamua can unload abnormally large coarse dust particles. "

These large grains of dust – which, surprisingly, are more difficult to spot than smaller grains – may be weak, but they are also massive enough to eject generates enough thrust to explain the unexpected increase in the Oumuamua speed. In addition, the researchers suggest that "Oumuamua can eject coarse grains because all the smaller grains of dust that adorn most cometary surfaces have already eroded during its long march through interstellar space.

Although the suspected degassing seems to tell us a little more about the composition of Oumuamua, unfortunately, it also makes it more difficult to determine the origin of this confusing object.

"The true nature of this enigmatic interstellar nomad can remain a mystery," said ESO co-author Olivier Hainaut. "The speed gain recently detected by Oumuamua makes it more difficult to trace the path that he borrowed from his extrasolar star."

With data from ESO's Very Large Telescope, NASA / ESA's Hubble Space Telescope and others, astronomers have concluded that "Oumuamua is probably a comet that undergoes degassing.

ESO