The probability of a large object colliding with Earth and exploding with the force of several thousand nuclear warheads is greater than the risk of dying in an air crash, a rocket scientist said.
An asteroid of 100 metres across would collide at about 25 kilometres a second and release about 100 megatons of explosive force 'that would be like a global nuclear war', Greg Canavan, of the Los Alamos National Laboratory in New Mexico, said. A lump of space rock 100m in diameter would release energy equivalent to the world's entire nuclear arsenal. An object 1km across - they do exist - would be like 1,000 nuclear wars, he said.
There is a 0.1 per cent risk in a lifetime of a massive object hitting Earth and doing terrible damage, Dr Canavan said. 'That's not an insignificant probability . . . The chances of being killed over a lifetime in an airplane is something like 0.01 per cent.'
He said asteroid impacts have the potential of wiping out life. 'Even the frequent impacts of smaller objects can cause significant losses . . . impacts by objects larger than a mile across could cause global catastrophe.'
Dr Canavan added that the risk to life justified further research into ways of detecting incoming objects. It would be feasible to build systems for early warning of a giant collision and use rockets, loaded with nuclear warheads, to deflect incoming asteroids.