Professor Stephen Hawking argued the laws of mathematics and physics mean an extinction-level asteroid impact is an unavoidable certainty.
The late cosmologist who died at the age of 76 in March this year, shared his dire thoughts in Brief Answers to the Big Questions – his last ever book.
Professor Hawking mused about the various scenarios in which human life cannot continue to exist on Earth.
He pondered the threat of nuclear war, climate change and the many dangers lurking in the depths of space.
Professor Hawking wrote: “The universe is a violent place. Stars engulf planets, supernovae fire lethal rays across space, black holes bump into each other and asteroids hurtle around at hundreds of miles a second.
“Granted, these phenomena do not make space sound very inviting, but these are the very reasons why we should venture into space instead of staying put.
“An asteroid collision would be something against which we have no defence.
“The last big such collision with us was about 66 million years ago and that is though to have wiped out the dinosaurs, and it will happen again.
“This is not science fiction; it is guaranteed by the laws of physics and probability.”
According to Dr Matija Cuk, an astronomer at Cornell University in New York, localised asteroid impacts occur every few hundred years.
These small-scale hits are not major threats to the planet but can slam into the Earth with the force of a hydrogen bomb.
The last known impact on this scale levelled vast swathes of the Siberian Tunguska forest in 1908.
A much small asteroid struck over Chelyabinsk Oblast in Russia in 2013, injuring 1,000 people with shattered glass caused by the asteroid exploding in the sky.
Dr Cuk said: “A regional destruction happens at intervals on the order of 100,000 years, and devastates an area a size of a mid-sized country.
“One such event we know of is an impact that occurred 700,000 years ago in Southeast Asia.
“These events usually involve one km-sized asteroids can leave craters tens of kilometres across.”
Global-level catastrophes involving six-mile (10km) asteroids appear to strike less often than every 10 million years.
One of these past impacts was likely responsible for the death of the dinosaurs.
Dr Cuk said the exact destructive potential of such an asteroid will depend on its composition and point of impact but it would kill “billions” of people regardless.
Thankfully, the asteroid expert said: “It is highly unlikely that a regional or global destruction would occur anytime soon – next couple of centuries – since we have already discovered most of near Earth asteroids larger than 1 km, and none of them seem to be heading this way.
“A localised impact has a less than a percent chance to happen in any given year, so the level of risk at any given place or time is also low.”