Still, while the title is sort of obvious (and almost question-begging), Bad Astronomer Phil Plait (who apparently hosts some TV show? I'm disconnected from the world since I have no TV) delves into some interesting details about what scientists have discovered about celestial bodies whose paths sometimes cross the path of our own little world, and even some of the ways in which we might be able to avoid such a collision in the future.
For more, check out our TEDTalks tag.