Asteroids...now, this is not Twitshit's fault.

The researchers propose several ways of doing this, the most extreme methods being to crash a spacecraft into the asteroid to knock it off course, or to set off a nuclear explosion. They say the earlier the threat is dealt with, the less drastic the course of action need be.

Obviously, the problem transcends asteroids. If you can change direction slightly at a point further away, you accomplish what you could otherwise have to do by changing it radically...Of course, if you take astronomy on faith, and figure that the dinosaurs just all ate some bad other dinosaur and palm, then you can wait, or assume that if the worst happens, it's just Tiffany bowling with big fucking rocks...