It sounds like the stuff of movies but the possibility of an asteroid collision is one of the things that we are vastly underprepared for. The United Nations is doing something about it:
“The U.N. plans to set up an “International Asteroid Warning Group” for member nations to share information about potentially hazardous space rocks. If astronomers detect an asteroid that poses a threat to Earth, the U.N.’s Committee on the Peaceful Uses of Outer Space will help coordinate a mission to launch a spacecraft to slam into the object and deflect it from its collision course. . .
The next step in defending Earth against dangerous asteroids is to find them, Lu said. “There are 100 times more asteroids out there than we have found. There are about 1 million asteroids large enough to destroy New York City or larger. Our challenge is to find these asteroids first before they find us.”
Early warning is important because it increases the chance of being able to deflect a threatening asteroid once it is found. If a spacecraft struck an asteroid 5 or 10 years before the rock was due to hit Earth, a slight orbital alternation should be enough to make it pass Earth by; if the asteroid wasn’t detected soon enough, evacuating the impact zone may be the only option available. “If we don’t find it until a year out, make yourself a nice cocktail and go out and watch,” Schweickart quipped.”
This is the type of public policy that individual governments are really bad at (because they can all hope someone else will take care of it). So it is nice to see the United Nations stepping up and working on a problem with catastrophic consequences.