Stephen Hawking has revealed he strongly believes in aliens and warned that Earth could be at risk from an invasion.
In a documentary series, the renowned astrophysicist argued that it is 'perfectly rational' to assume intelligent life exists elsewhere in the universe.
And in an extraordinary series of assertions, he said Earth might be at risk from what he imagines to be 'massive ships' which could try to colonise our planet and plunder our resources.

Professor Hawking said: 'We only have to look at ourselves to see how intelligent life might develop into something we wouldn’t want to meet. 'I imagine they might exist in massive ships, having used up all the resources from their home planet.

'Such advanced aliens would perhaps become nomads, looking to conquer and colonise whatever planets they can reach.'
It would be 'too risky' to attempt to make contact with alien races, he concluded.

'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.

The 68-year-old eminent scientist has spent three years working on the Discovery Channel documentary series, Universe, despite being paralysed by motor neurone disease.
Professor Hawking, who communicates using a speech synthesizer, re-wrote large parts of the script and kept a close eye on the filming.
The programmes use imagined illustrations to explain why he believes in extraterrestrial life and the forms it could take.
The scientist said that most alien life is likely to consist of small animals or microbes in planets, stars or floating in space.
But in one scene, shoals of fluorescent animals are depicted living under thick ice on Europa, one of Jupiter's moons, while flying yellow predators prey on two-legged herbivores in another.

The existence of 100 billion galaxies each containing hundreds of millions of stars means Earth is unlikely to be the only place where life has evolved, Professor Hawking said.
'To my mathematical brain, the numbers alone make thinking about aliens perfectly rational. The real challenge is to work out what aliens might actually be like,' he added.
New series: Stephen Hawking revealed he believes in life on other planets
Professor Hawking has suggested an open-minded attitude to extraterrestrials before, but the discovery of more than 450 previously-unknown planets orbiting distant stars since 1995 is believed to have strengthened his belief.
This year Professor Brian Cox, a physicist from the University of Manchester, also suggested life may exist elsewhere within our solar system - on Mars or the moons orbiting Jupiter or Saturn.
Britain's leading astronomer also provoked controversy by saying that the chance of detecting alien life was stronger than ever before.
Lord Rees, the Astronomer Royal and president of the Royal Society said: 'I suspect there could be life and intelligence out there in forms that we can’t conceive.

'And there could, of course, be forms of intelligence beyond human capacity, beyond as much as we are beyond a chimpanzee.'
Stephen Hawking's Universe begins on the Discovery Channel on Sunday May 9 at 9pm.
Executive producer John Smithson said: 'He wanted to make a programme that was entertaining for a general audience as well as scientific and that’s a tough job, given the complexity of the ideas involved.'