But that idea, while exciting to many, is preposterous and just "wild speculation," according to the physicist and astronomer who discovered it.
Speaking with CBC, Canadian physicist and astronomer Robert Weryk said the theory put forth by postdoctoral researcher Shmuel Bialy and professor Abraham Loeb, the director at the CfA's Institute for Theory and Computation, is wild speculation.
"There's a maximum speed that you can be traveling to be bound gravitationally by the sun," Weryk told the Canadian outlet. "When we first saw this object, it was traveling faster than that, so we know for a fact that it's from outside our solar system. We decided that it was a comet that had a bit of outgassing that wasn't visible from the ground, which is why it didn't appear to be a comet."
He continued: "(The Harvard researchers) decided to focus on another aspect of that, that it's an alien spacecraft and that it has a solar sail type material that's causing the non-gravitational trajectory. But we actually believe that's not true based on the data we obtained."
In an email to Fox News, Loeb said his and Bialy's paper "attempts to explain the excess force" that acted on Oumuamua when observed and Weryk's reaction "shows prejudice."
"Our paper follows the standard scientific methodology: an anomaly is observed in data, the standard explanation fails to explain it and so an alternative interpretation is proposed," Loeb wrote in the email. "I encourage anyone with a better explanation to write a paper about it and publish it. Any wrong interpretation can be ruled out when more data will be released on `Oumuamua or other members of its population in the future. A reaction of the type you quoted shows prejudice."
Weryk made the discovery of Oumuamua, which is the Hawaiian name for "pathfinder" or "scout," in October 2017 with the PanSTARRS1 telescope.
In their paper, Bialy and Loeb theorized it could be a "lightsail, floating in interstellar space as a debris from an advanced technological equipment."
The paper continued: "Lightsails with similar dimensions have been designed and constructed by our own civilization, including the IKAROS project and the Starshot Initiative. The lightsail technology might be abundantly used for transportation of cargos between planets or between stars."
The researchers even theorized that Oumuamua "may be a fully operational probe sent intentionally to Earth vicinity by an alien civilization," though that scenario was called "exotic."
Since its discovery, researchers have debated whether it is a comet or an asteroid, though it was eventually determined to be a comet. NASA ruled that it is a "metallic or rocky object" approximately 400 meters (1,312 feet) in length and 40 meters (131 feet) wide.
Oumuamua is traveling away from the Sun at a rate of approximately 70,000 mph, towards the outer part of the solar system. In approximately four years, it will whiz past Neptune's orbit, on its way to interstellar space.
So what does Weryk believe it is?
"I think it's a remnant from another solar system. It's just something that happened to run into us, and we were very lucky to have been operating the telescope that night and looking in that direction," Weryk told CBC.
He added: "It's been theoretically predicted for decades but we've never seen one. Until we see another one, there are a lot of questions that we just can't answer."
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