Late in 2017, scientists discovered the object ' Oumuamua, which was something of a mystery to scientists, with theories about what it is ranging from a comet or asteroid to an alien messenger craft Harvard University astronomer Avi Loeb led the alien theory, telling Universe Today in October 2018: "We explain the excess acceleration of ‘Oumuamua away from the sun as the result of the force that the sunlight exerts on its surface. "For this force to explain measured excess acceleration, the object needs to be extremely thin, of order a fraction of a millimetre in thickness but tens of meters in size."This makes the object lightweight for its surface area and allows it to act as a light sail. Its origin could be either natural (in the interstellar medium or proto-planetary disks) or artificial (as a probe sent for a reconnaissance mission into the inner region of the solar system) .”Nonetheless, four months on, Prof Loeb, who is chairman of the Harvard Astronomy Department, is refusing to back down from his claims and is now challenging anyone to prove him wrong.Now, in an interview to Washington Post Loeb said, to support his theory he wrote the equation that an extraterrestrial spacecraft, or at least a piece of one, may at this moment be flying past the orbit of Jupiter."It changes your perception on reality, just knowing that we're not alone," Avi Loeb said.The astronomer thinks that Oumuamua is not a comet or asteroid, as his colleagues suggest, but a lightsail that was once the driving force of "advanced technological equipment". Loeb points out that the interstellar object is moving too fast for an inert piece of rock as if something is pushing it from behind. He also doesn't think it's a comet, as observations of the object haven't revealed anything resembling a comet's tail.Loeb believes that the mainstream image of Oumuamua as a piece of potato-shaped rock is actually wrong. According to the astronomer, it's a kilometer-long and 1-millimeter-thick obloid lightsail, which is so light and thin that it's capable of "catching" the sun's rays and uses them as "wind" propelling it further into space. So far scientists have been unable to determine the exact shape of the object due to its complex rotation, but they suggest it is a "cigar-shaped" rock.