Astronomers from Harvard University have published a new research letter arguing that a mysterious object spotted in our solar system last year could have been an alien spacecraft.

The unusual-looking oblong object was discovered in October 2017 by the Pan-STARRS 1 telescope in Hawaii and nicknamed ‘Oumuamua, meaning “a messenger that reaches out from the distant past” in Hawaiian. Unable to determine what it was or where it had come from, scientists determined that it was not an asteroid or a comet, and eventually dubbed it the first-ever instance of a new classification of “interstellar object.”

“One possibility is that ‘Oumuamua is a lightsail, floating in interstellar space as a debris from an advanced technological equipment,” suggests the letter, which was written by Abraham Loeb, professor and chair of astronomy, and Shmuel Bialy, a postdoctoral scholar, at the Harvard Smithsonian Center for Astrophysics, and has not yet been through the peer review process. A lightsail is a kind of propulsion that spacecraft use, where light from the sun moves the craft forward like wind in the sail of a sailboat.

“A more exotic scenario is that ‘Oumuamua may be a fully operational probe sent intentionally to Earth vicinity by an alien civilization,” the paper says, siting a discrepancy between the trajectory the object took and projections of how an object of its size should move through space. “This discrepancy is readily solved if ‘Oumuamua does not follow a random trajectory but is rather a targeted probe.”

Robert Weryk, the University of Hawaii physicist who first spotted the object, told Vice’s Motherboard that he’s not convinced by Loeb and Bialy’s suggestions. “There is no reason to believe `Oumuamua is anything but a natural object (a comet from another solar system) based on the observations that were obtained by the team I worked with,” Weryk said. “It is true though, that there really is a lot we do not know about interstellar comets, and it really will take us finding more of them to better understand them. This may take a while, but now that we know they exist, we are looking more closely at each new [near-Earth object] discovery we make.”