When United Airlines workers reported a UFO at O'Hare Airport in November 2006, it was met with the typical denials and hush-up that usually accompany such sightings. But when a related story broke the record for hits at the Chicago Tribune's website, it was clear that such unexplained objects continued to occupy the minds of fascinated readers. Why, wonders Thomas Bullard, don't such persistent sightings command more urgent attention from scientists,...