Named after the evil Egyptian serpent god Apophis, lord of chaos and darkness -- and recently dubbed the "doomsday asteroid" -- flies past Earth every seven years. This year, its 1,000-foot bulk approached to within 9 million miles. However, in 2029, it will swoop in close enough to put some of our orbiting satellites in peril -- 20,000 miles. In that year, no doubt Apophis will arouse even more attention because it will be visible in the daytime sky. Yet there's always a possibility we don't have these measurements exactly right. Something could happen at any point in Apophis' orbit to modify its course, just a smidgen. A tiny collision with another object, way out beyond Mars? What could change between now and 2029, or during any orbit thereafter?