A meteor caused a massive explosion over Earth last year, but nobody noticed until now. It is the second-largest recorded impact in the past century, after the meteor that exploded over the Russian region of Chelyabinsk in 2013 .

The giant fireball hit at 2350 GMT on 18 December over the Bering Sea, a part of the Pacific Ocean between Russia and Alaska.

Peter Brown at the University of Western Ontario, Canada, …