Scientists are unsure of the 460-foot-wide rock's exact composition, or how devastating its impact would be. But after observing the space rock's orbit, they've calculated a 1-in-625 chance that the asteroid called 2011 AG5 could collide with Earth on Feb. 5, 2040. "2011 AG5 is the object which currently has the highest chance of impacting the Earth," says Detlef Koschny of the European Space Agency.

http://news.yahoo.com/could-humongous-asteroid-really-hit-earth-2040-134500007.html