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.
Now, a new paper by researchers at the Harvard Smithsonian Center for Astrophysics raises the possibility that the elongated dark-red object, which is 10 times as long as it is wide and traveling at speeds of 196,000 miles per hour, might have an "artificial origin".
Oumuamua's unusual trajectory and high speed sets it aside from other space objects such as asteroids and comets.
At first, astronomers thought the rapidly moving faint light was a regular comet or an asteroid that had originated in our solar system. In fact, in their article, published this week in the The Astrophysical Journal Letters, they claim the object "may be a fully operational probe sent intentionally to Earth vicinity by an alien civilization". 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.
"It is impossible to guess the objective behind Oumuamua without more data", Avi Loeb, chairman of Harvard's astronomy department and a co-author of the paper, told NBC News in an email. "If Oumuamua is a lightsail", he added, "one possibility is that it was floating in interstellar space when our solar system ran into it, "like a ship bumping into a buoy on the surface of the ocean".
Ariana Grande credits therapy with saving her life
I know they say I move on too fast, but this one gon" last "cause her name is Ari, and I'm so good with that'. She sings: 'Thought I'd end up with Sean, but it wasn't a match.
Mr Loeb is an adviser to Breakthrough Starshot, an initiative that plans to send a fleet of tiny laser-powered lightsail craft to the nearest star system.
Alongside Shmuel Bialy, a postdoctoral fellow at the Harvard-Smithsonian Center for Astrophysics, acknowledges that the alien spacecraft theory is an "exotic" one.
"It's certainly ingenious to show that an object the size of Oumuamua might be sent by aliens", says SETI Institute astronomer Seth Shostak. "One should not blindly accept this clever hypothesis when there is also a mundane (and a priori more likely) explanation for Oumuamua".
He said: "If it were a spacecraft, this tumbling would make it impossible to keep any instruments pointed at the Earth".
When the object was first spotted scientists believed it might have been travelling through space for hundreds of millions of years.
The truth may be hard to establish, as Oumuamua has left the solar system and is no longer visible even with telescopes.