First spotted by the Pan-STARRS 1 telescope in Hawaii in October 2017, the odd, fast-moving object has puzzled astronomers since its discovery.
In late October, 2017, NASA said the recently discovered interstellar visitor appeared "to have originated from outside the solar system, coming from somewhere else in our galaxy".
That's why the researchers raise the possibility that Oumuamua's an alien craft in the new issue of Astrophysical Journal Letters. The excess acceleration of Oumuamua was detected at multiple times, ruling out an impulsive kick due to a break up of the object.
"It is impossible to guess the goal behind Oumuamua without more data, [but the object] may be a fully operational probe sent intentionally to Earth vicinity by an alien civilization".
Loeb and his collaborator, Shmuel Bialy, a postdoctoral fellow at the Harvard-Smithsonian Center for Astrophysics, acknowledge the alien spacecraft scenario is an "exotic" one - and other scientists are doubtful.
The change in course and speed was so pronounced they concluded it "might be a lightsail of artificial origin".
"This would account for the various anomalies of 'Oumuamua, such as the unusual geometry inferred from its light-curve, its low thermal emission, suggesting high reflectivity, and its deviation from a Keplerian orbit without any sign of a cometary tail or spin-up torques".
The Harvard scientists speculated that solar radiation hitting a solar sail could explain why the mysterious object started moving faster.
Oumuamua has already passed Earth on its way out of the solar system, so the object is too far away for scientists to continue studying it, meaning its origin, behaviour, and makeup will remain a mystery.
But until science tells us that it definitely isn't, we'd like to believe that it is. "The approach I take to the subject is purely scientific and evidence-based".
But SETI senior astronomer Seth Shostak said in an email to NBC that "one should not blindly accept this clever hypothesis when there is also a mundane explanation for 'Oumuamua - namely that it's a comet or asteroid from afar".
He raised questions in particular about the object's tumbling motion. It's also possible Oumuamua was just created to wander through space, collecting information, and our solar system just happened to be in its way - its operators weren't necessarily looking to pry into the lives of humans. Loeb is saying that the Oumuamua doesn't exhibit the type of characteristics seen in other comets and asteroids.
"Two very capable, very bright astronomers, from a very credible organization, Harvard, have come out with the notion that Oumuamua could be alien in origin", Diamond said.