Meteor risk 'bigger than thought'

The threat of space rocks smashing into Earth is bigger than previously thought, say scientists studying the terrifying meteor that exploded without warning over a Russian city last winter.

Meteors about the size of the one that streaked through the sky at 42,000 mph (67,600 kph) and burst over Chelyabinsk in February – and ones even larger and more dangerous – are probably four to five times more likely to hit the planet than scientists believed before the fireball, according to three studies published in the journals Nature and Science.