Bill Diamond, president and CEO of the SETI Institute, said he thinks it is likely Oumuamua is simply an asteroid, but said he has no problem with Loeb's conclusions.
When Oumuamua was spotted a year ago, scientists observed that its speed had increased after passing the Sun.
At the end of the day, however, there's no way to know for sure.
This mysterious object, spotted tumbling through our solar system past year, may have been an alien spacecraft sent to investigate earth.
A Hawaiian telescope first spotted "Oumuamua", meaning "a messenger from afar, arriving first" in Hawaiian, in October 2017.
The truth may be hard to establish, as Oumuamua has left the solar system and is no longer visible even with telescopes.
"Recent observational and theoretical studies imply that 'Oumuamua is not an active comet", the researchers said in a draft version of their study. But they found nothing.
"Observational anomalies like we see with Oumuamua, combined with careful reasoning, is exactly the method through which we make new discoveries in astrophysics - including, perhaps, truly incredible ones like intelligent life beyond the Earth", he wrote.
That's the most "exotic" explanation provided in a paper set to be published November 12 in The Astrophysical Journal Letters, written by researchers from the Harvard Smithsonian Center for Astrophysics.
"For decades we've theorized that such interstellar objects are out there, and now―for the first time―we have direct evidence they exist", said Thomas Zurbuchen, associate administrator for NASA's Science Mission Directorate in a 2017 news release.
If the interstellar object is as thin as astronomers estimate it to be, Loeb and Bialy suggest it could be a light sail, which is conceived as able to harness light or solar energy from the sun to propel a spacecraft. Humans have experimented before with lightsails, but the idea remains in its infancy.
According to two Harvard astronomers, the shape could have been a "fully operational probe sent intentionally to Earth vicinity by an alien civilization".
If the object is a lightsail, the paper adds it might have been floating in interstellar space when our solar system ran into it "like a ship bumping into a buoy on the surface of the ocean". That and the object's odd movements suggest it could have a source of power beyond gravitational pulls, they said.
According to Harvard scientists, we may not be alone in our solar system. So the Harvard authors' "exotic" guesses are just as good as anyone's at this point.
The paper was written by Abraham Loeb, professor and chair of astronomy, and Shmuel Bialy, a postdoctoral scholar, at the Harvard Smithsonian Center for Astrophysics.