A cigar-shaped interstellar object that flew past the sun probably isn't an alien spacecraft, scientists are saying, despite the suggestion by researchers from Harvard University.
Scientists have been trying to figure out what the 1,312ft (400m) object named Oumuamua might be after it was first spotted by a telescope in Hawaii in October 2017.
The object's flat, elongated shape and reddish colour is from outside our solar system, according to the researchers.
It was moving at 59,030mph when it was first tracked by scientists, and its unusual trajectory and high speed sets it aside from other space objects such as asteroids and comets.
Earlier this week, researchers from Harvard suggested it "may be a fully operational probe sent intentionally to Earth vicinity by an alien civilisation".
Speaking to AFP, a number of astronomers have challenged the Harvard scientists' suggestions.
"Like most scientists, I would love there to be convincing evidence of alien life, but this isn't it," said Dr Alan Fitzsimmons of Queens University Belfast.
"It has already been shown that its observed characteristics are consistent with a comet-like body ejected from another star system.
"And some of the arguments in this study are based on numbers with large uncertainties."
Another well-known astrophysicist, Dr Katie Mack from North Carolina State, was critical of the claim on Twitter.
The thing you have to understand is: scientists are perfectly happy to publish an outlandish idea if it has even the tiniest *sliver* of a chance of not being wrong. But until every other possibility has been exhausted dozen times over, even the authors probably don’t believe it.— Katie Mack (@AstroKatie) November 6, 2018
"The thing you have to understand is: scientists are perfectly happy to publish an outlandish idea if it has even the tiniest *sliver* of a chance of not being wrong.
"But until every other possibility has been exhausted dozen times over, even the authors probably don't believe it."
In a letter in The Astrophysical Journal Letters, Dr Shmuel Bialy and Dr Avi Loeb claimed that Oumuamua could be a spacecraft pushed along by light falling on its surface - a theoretical form of space transportation known as a "light sail".
AFP asked Dr Bialy if he believed his claim. He admitted: "I wouldn't say I 'believe' it is sent by aliens, as I am a scientist, and not a believer, I rely on evidence to put forward possible physical explanation for observed phenomena."
Dr Loeb, who is the chairman of Harvard's astronomy department, told NBC News: "It is impossible to guess the purpose behind Oumuamua without more data."