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Hawking detailed his fears in Brief Answers to Big Questions – his last ever book, which was published this week after the authors' death in March.
The physicist said throughout his life doomsday space rocks monitored by NASA are a threat to humanity and any other intelligent civilization that exists in our universe.
And in his final musings, the scientist, who has died aged 76, considered scenarios in which human life can not continue to exist on Earth.
He wrote about the threat of nuclear war, and the dangers of space.
The late cosmologist said: "The universe is a violent place. Stars engulf planets, supernova 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 defense.
"The last big such collision was over 66million years ago, and that is going to be a dinosaur, and it will happen again.
"This is not science fiction; it is guaranteed by the laws of physics and probability. "
The last known asteroid impact leveled vast swathes of the Siberian Tunguska forest in 1908.
PREDICTION: Professor Stephen Hawking said asteroid could destroy Earth (Pic: Getty)
DESTRUCTION: Scientists monitor the skies for asteroids (Pic: Getty)
A much smaller asteroid struck over Chelyabinsk Oblast in Russia in 2013, injuring 1,000 people with shattered glass caused by the asteroid exploding in the sky.
Our solar system is packed full of gigantic space rocks, some of which are more than 1 kilometer in size.
We are tracking the movements of about 90% of these, which would wipe out if they plowed into Earth.
That means there are a lot of rogue rocks that could be a collision course with our planet.
Michel said: "We only know about 15 or 20% of the items which are larger than a few hundred meters in size.
IMPACT: A massive meteor smashed into the Russian city of Chelyabinsk in 2013 (Pic: IG)
DANGER: Dinosaurs went extinct when a massive asteroid smashed into Earth (Pic: Getty)
Astronomer Patrick Michel previously said: "If these bodies impact Earth, they can cause a regional breakdown of a country or even a continent."
There are several ways to tackle asteroids.
The first would involve a "gravity tractor", which is essentially a space ship designed to gravitate to a new path using its own gravitational pull.
Others would involve blasting the space rock with some sort of projectile to try and steer it onto a new race, or even blowing it up with a nuke.
However, this could be the cause of radioactive rock fragments to rain down on the planet.
Astronomer Carolyn Shoemaker is an expert on asteroids.
LIVING MEMORY: Professor Hawking's Children Lucy and Timothy at the book launch (Pic: Getty)
"An asteroid collision would be something against which we have no defense"
Hawking
She discovered Comet Showmaker-Levy 9, which broke apart and then spectacularly plunged into Jupiter.
She called for more study of doomsday space rocks.
"The more we learn about these things, the more we can be prepared for an impact that would be dangerous to us."
Global-level disasters involving six-mile (10km) asteroids appear to strike less often than every 10million years.
One of these past impacts was responsible for the death of the dinosaurs.
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