A mountain-sized asteroid which passes Earth every three years has been discovered by a Russian scientist.
Vladimir Lipunov, a professor at Moscow State University, said the space rock, named '2014 UR116', poses no immediate threat - although warned it could 'theoretically' hit Earth..
However, he said it highlights the damage an asteroid could cause - in this case an explosion 1,000 times greater than the surprise 2013 impact of a bus-sized meteor in Russia.
Prof Lipunov said it is difficult to calculate the orbit of big rocks like '2014 UR116' because their trajectories are constantly being changed by the gravitational pull of other planets
'We need to permanently track this asteroid, because even a small mistake in calculations could have serious consequences,' he said.