The next time a large object falls out of the sky, we may be taken by surprise-currently, there is no early warning system for near-Earth objects. However, over the next decade, sky surveys, like the one being done by Tholen, should begin filling that gap. Astronomers are compiling a list of thousands of asteroids to help us anticipate the next strike. "Every couple of weeks," says former astronaut Lu "we're going to be finding another asteroid with, like, a one-in-a-thousand chance of hitting the Earth.