SEARCHING FOR THE NEXT ONE
We do not know when Earth will be hit again. Statistically, a 6 mile (10 km) diameter comet—large enough to cause a mass extinction—should strike once every 100 million years. Smaller 1/2 mile (1 km) diameter objects could strike every 100,000 years, and would certainly still be devastating.
Astronomers are hoping to get funding to systematically survey the sky for impact hazards, plotting the orbit of every asteroid or comet that could inflict global damage. The numbers are daunting—there are millions of objects to be discovered and sifted through to identify the 2,000 or so most dangerous ones.
Next time a cornet "stalks the sky," we should enjoy its beauty and mystery. And as we gaze, we should be mindful of the awesome potential for disaster should such an object strike the Earth. But also remember: were it not for such an impact, 65 million years ago, we quite possibly would not be here today.