Another event like the K/T impactor could happen at any time. We often find objects on the way out from the earth/moon system that passed within a lunar orbit of the earth as they went by. Even if we find objects coming toward us, we really have no way to deflect them. Averaged over a huge time interval, the probability that you will be killed by an asteroid is similar to the possibility that you will be killed in a car accident. However, the probability of any such event in your lifetime is low. From the graph of megatons equivalent TNT vs. frequency, something like the K/T event happens rarely, over many million years. When it happens, however, so much devastation occurs that it makes up for its rarity in total effect. (to left by Gary Larson, The Far Side, to right by Gahan Wilson, from the New Yorker, 10/2/2000)