The object, nicknamed 'Oumuamua, meaning "a messenger that reaches out from the distant past" in Hawaiian, was first discovered in October 2017 by the Pan-STARRS 1 telescope in Hawaii.
It was moving at 59,030mph when it was first tracked by scientists.
However, it seems unlikely that we'll ever know if Oumuamua did, in fact, have an artificial light sail.
Shmuel Bialy and Abraham Loeb, two astronomers from the Harvard Smithsonian Centre for Astrophysics, suggested the cigar-shaped object - given the Hawaiian name 'Oumuamua, which NASA notes "means a messenger from afar arriving first" - could have been a discarded light sail of extra-terrestrial origin, perhaps sent here on objective.
Harvard researchers have now said it "may be a fully operational probe sent intentionally to Earth vicinity by an alien civilisation".
Oumuamua's unusual trajectory and high speed sets it aside from other space objects such as asteroids and comets.
The change in course and speed was so pronounced they concluded it "might be a lightsail of artificial origin".
The researchers are not saying outright that Oumuamua is a sign of extraterrestrial life.
In a paper to be published November 12 in The Astrophysical Journal Letters, the pair declare that the reddish, elongated, stadium-sized object "may be a fully operational probe sent intentionally to Earth vicinity by an alien civilization", NBC News reported.
According to Harvard scientists, we may not be alone in our solar system.
"I am distinctly unconvinced and honestly think the study is rather flawed", Alan Jackson, fellow at the Centre for Planetary Sciences at the University of Toronto Scarborough, told CNN. "The approach I take to the subject is purely scientific and evidence-based".
Of course, the pair aren't claiming that Oumuamua's definitely of alien origin. "But one should not blindly accept this clever hypothesis when there is also a mundane (and a priori more likely) explanation for Oumuamua - namely that it's a comet or asteroid from afar".
He raised questions in particular about the object's tumbling motion.
Oumuamua has left the solar system and is no longer visible, the news outlet noted.
When the object was first spotted scientists believed it might have been travelling through space for hundreds of millions of years.
"Why send a spacecraft which is doing this?" he said.
"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.