The November Nemesis

Meteors and comets have struck Earth repeatedly. One may have wiped out the dinosaurs 65 million years ago. The big question, of course, is when will the next one hit? Peter Jenniskens, an astronomer at the NASA Ames Research Center near Mountain View, California, hasn’t found the next killer comet, but he has discovered something almost as ominous: the orbit of an as yet unseen comet that could one day slam into Earth.