The famed physicist said monster space rocks were one of the biggest threats to humanity and will wipe out all life on the planet.
Speaking in a video made by Asteroid Day - the global campaign movement backed by Queen legend Brian May - Professor Stephen Hawking said: “One of the major threats to intelligent life in our universe is the high probability of an asteroid colliding with inhabited planets.”
Asteroid Day wants more done to develop ways of deflecting an asteroid on collision course with Earth, and to identify all the unknown asteroids out there which could impact us.
Astronomer Patrick Michel said: “We only know about 15 or 20 per cent of the objects which are larger than a few hundred metres in size.
“If these bodies impact Earth, they can cause regional damage across a whole country or even a continent.”
Stephen Hawking claims an asteroid will one day threaten life on Earth.
NASA says an asteroid should not hit Earth for at least 100 years.
One of the major threats to intelligent life in our universe is the high probability of an asteroid colliding with inhabited planets.
Currently there is no tested way of dealing with an asteroid on a collision path with the planet.
But ideas include sending a space ship to use its own gravity to move it off course.
The idea of nuking it in space has effectively been ruled out, as this would send thousands of smaller fragments hurtling at us over a wider area.
Astronomer Carolyn Shoemaker said: "The more we learn about all of these objects, the more we can be prepared for preventing an impact that would be dangerous to us.”
NASA says it keeps a close eye on asteroids, and none is expected to hit the planet for at least the next 100 years.