Nasa already has a space probe on route to Bennu to take samples and has been monitoring the asteroid since it was discovered in 1999.

Although there is little risk it could hit the Earth, it is still considered as an NEO, or Near Earth Object, which would hit the planet with 1,450 megatons of TNT.

The Atomic Energy Commission has shown that a one gigaton warhead detonated about 10 miles up could be expected to start fires over an area of more than 430,000 square miles, an area more than four times the size of Britain.

Dante Lauretta, professor of Planetary Science in the Lunar and Planetary Laboratory at the University of Arizona, said  Bennu’s impact would release “three times more energy than all nuclear weapons detonated throughout history”.

"The impact would release energy equivalent to 1,450 megatons of TNT," he said.

“For comparison, the fission bombs used in World War II had an energy release of roughly 20 kilotons of TNT each and the most powerful nuclear weapon ever detonated, the Russian Tsar Bomba, had a yield of 50 megatons."

However the study showed that Earth would need years of warning to be able to put a deterrent plan in action.

The experts calculate that 7.4 years would be needed from building Hammer, to the craft hitting the asteroid.

Earth is hit by asteroids with surprising regularity but most are too small to do much damage or fall in unpopulated areas. In 2013, a meteor airburst over Chelyabinsk, Russia, broke shattered windows for over 300 miles.

+++