A Harvard University professor has stirred up the debate about aliens by suggesting we're probably not alone in the universe.

Astronomer Avi Loeb's claim comes after examining a fly-by of an object in space that he believes was truly out of this world.

The cigar-shaped object seen by telescopes was dubbed 'Oumuamua' – meaning 'a messenger that reaches out from the distant past' in Hawaiian.

It was 10 times as long as it is wide and was traveling at speeds of 196,000 mph, researchers said at the time.

"At first people thought, 'Well it must be a rock, just like the asteroids or comets that we have seen before within the solar system'," Loeb told CBSN Boston's Paula Ebben. "But as they got more data on it, it looks very weird.

"It didn't look like a comet, yet it behaved some like something that has an extra push," Loeb said.

NASA confirmed of the 2017 sighting that it's "the first object ever seen in our solar system that is known to have originated elsewhere," but said its origins are unknown.

Loeb argues in his book 'Extraterrestrial' that the object was probably debris from advanced alien technology – space junk from many light years away. It may have been a type of 'light sail' propelled by sunlight, a technology that humans are currently developing for space exploration. "It's possible that there is a lot of space junk out there or it is a probe," he said. "We don't know because we didn't collect enough data, enough evidence and I'm just alerting everyone to look for objects like that so that next time there is one coming by we will examine it more carefully."

Loeb said it's time for researchers to look for potential 'messages in a bottle' like Oumuamua instead of just searching for radio signals as evidence of other civilisations.

He said his ideas aren't popular in the scientific community right now – talking about potential extra-terrestrial intelligence is 'out of the mainstream, and it should not be', he said.