“Data show that crashing a sacrificial spacecraft into an asteroid would be powerful enough to avoid almost all rocks hitting Earth, averting catastrophe.
Only asteroids wider than a kilometre would need a nuclear detonation to shift them off course, scientists now believe.
A rock this big is expected to hit our planet once every 700,000 years and would create a crater as big as Manchester. An impact of this size would cause global devastation and the possible collapse of civilisation, experts say.
Astronomers believe around 900 “near Earth objects” – defined as within 120 million miles of our sun – are more than one kilometre wide, and they have identified 95 per cent of them.
Nuclear warheads have long been, and continue to be, part of planetary defence plans, but only as a last resort.
A White House document recently said that the US would continue to study when a nuclear explosive device would be needed to prevent an asteroid apocalypse.”
https://www.yahoo.com/news/scientists-reveal-way-stop-giant-131134166.html