The US space agency is drawing up plans to land an astronaut on an asteroid hurtling through space at more than 30,000 mph. It wants to know whether humans could master techniques needed to deflect such a doomsday object when it is eventually identified. The proposals are at an early stage, and a spacecraft needed just to send an astronaut that far into space exists only on the drawing board, but they are deadly serious. A smallish asteroid called Apophis has already been identified as a possible threat to Earth in 2036.
UPDATE: More on asteroid impacts here.