We still do not know what it is, but a priori, Oumuamua is not an extraterrestrial vessel. Discovered in 2017, Oumuamua is the first interstellar visitor ever observed, the first object not originally formed in our solar system. In a new study published on Monday, July 1 in Nature, an international team of researchers takes stock of what is known about this strange “object”, neither really comet nor really asteroid.
Since the first observation of Oumuamua, its history and nature have never ceased to astonish and divide scientists. It must be said that its elongated cigar shape, its hiccuping trajectory and its composition make this object a very singular case. So much so that some researchers have even mentioned the track of an extraterrestrial probe. A hypothesis that was then criticized by many researchers.
In the study that has just been published, the researchers gathered all the information collected around Oumuamua, compiling the observations made by several telescopes, in order to establish a synthesis of what is known about this interstellar visitor.
And while there are still many uncertainties, the researchers believe that Omuamua, six times longer than wide, has no reason to be an extraterrestrial probe.
One of the main arguments was the acceleration of the interstellar visitor. It could have been due, as with comets, to a release of gas and dust that would propel it. But none of this has been observed by telescopes.
So, some researchers thought, it could mean that the object was accelerating, like a spaceship. And given its elongated shape, some even thought is a solar sail, a promising type of engine, currently tested in space.
But in their study, the authors explain that it is impossible in the current circumstances. “The argument of the solar sail is that Umuamua should be aligned with our sun to have the acceleration that we observe,” says Matthew Knight, co-author of the study. Problem: Oumuamua does not go straight: it turns on itself in a strange way. One could even say that it tumbles more than it turns.
In this context, a solar sail could not explain its acceleration. So what can? “Oumuamua could be releasing water vapor [which would propel it, Editor’s note], just at a lower level than it needed to be detected by our observations,” continues Matthew Knight.
Oumumua remains very mysterious. Its shape, its strange rotation, or its origin are all characteristics that we have not elucidated. However, say the researchers, there are a lot of plausible natural explanations, listed in the study. “I see no reason to invoke something as extraordinary [as extraterrestrials, Ed] unless you have worn out all other explanations,” said Matthew Knight.
Fortunately, we should in a few years discover many other interstellar objects. Future telescopes, such as the LSST under construction, should allow us to detect many stars located far away from the Earth, in the Oort cloud, which defines the ultimate boundary of the solar system. Comets, but also interstellar visitors.
The OHSA is expected to allow us to detect approximately one equivalent of Oumuamua per year. And that’s not all. The European Space Agency has just announced a future mission, “Comet Interceptor”, which could simply go to meet an interstellar object.