Graphic: The destruction radius if Asteroid DA14 had hit Toronto, and other fun facts about space rocks hitting the Earth

A space rock even bigger than the meteor that exploded like an atom bomb over Russia could drop out of the sky unannounced at any time and wreak havoc on a city. And Hollywood to the contrary, there isn't much the world's scientists and generals can do about it.

But some former astronauts want to give the world a fighting chance.