Photo: © 2008 AP via AAP/Lawrence Jackson
Hawking says extraterrestrials are almost certain to exist somewhere in the billions of galaxies and numerous star systems out there.
But he warns that contact with them could be disastrous for us.
"To my mathematical brain, the numbers alone make thinking about aliens perfectly rational," he says in his new documentary series.
"The real challenge is to work out what aliens might actually be like.
"If aliens ever visit us, I think the outcome would be much as when Christopher Columbus first landed in America, which didn’t turn out very well for the Native Americans."
