First, the bad news: You’ve just heard that an asteroid or a comet is about to wallop Earth and you might be in the vicinity. Now for some good news: You can find out just how severe the collision will be by logging on to http://www.lpl.arizona.edu/impacteffects/.
Type in your distance from the predicted impact site, as well as the size and kind of projectile, and an easy-to-use program calculates the energy of the impact and the extent of the hole it will gouge.