That margin of mystery continues to thrill diehard believers around the world, many of whom have organized into groups dedicated to studying UFOs and cataloguing and tracking sightings. The Mutual UFO Network, for example, boasts about 3,000 members in all 50 states and more than a dozen countries. MUFON receives about 500 reports of UFO sightings a month, and some 1,000 volunteers investigate what they see as the most credible ones by interviewing witnesses and collecting photos, radar data, and other evidence.
A big challenge for amateur and professional researchers is the large number of sensational reports that later prove to be hoaxes. In 2009, local television stations reported witness sightings of strange red lights moving through the evening sky around Morristown, N.J., on several days in January and February. As coverage spread nationally, the History Channel series UFO Hunters featured the story. In early April, however, two local men admitted they had created the floating lights by attaching flares to helium balloons, to poke fun at UFO investigators and to demonstrate how unreliable eyewitness accounts are. The mysterious crop circles that have for centuries inexplicably appeared in fields around the world are often held out by some UFO buffs as markings left by alien craft. But skeptics scoff, saying they could easily have been man-made. Such stories frustrate serious researchers. "It really gets hard to separate the wheat from the chaff," acknowledges Bruce Maccabee, a former U.S. Navy research physicist and MUFON state director.
In fact, many scientists and skeptics don't feel that systematically studying UFOs is a valuable endeavor.
"I just don't think the evidence is very good," says Seth Shostak, senior astronomer with the SETI (Search for Extraterrestrial Intelligence) Institute, a research organization based in Mountain View, Calif.
But Kean is convinced that there are enough puzzling cases for officials to give the subject a fresh look. In 1999, she was given a report produced by a group of French military officers, scientists, engineers, and others examining a spate of seemingly unexplained UFO sightings across the world. She was struck by the credibility of the investigators, who concluded there was a need for more careful analysis of these "unknown flying machines" that appeared "guided by a natural or artificial intelligence." The report inspired her to review once-classified government documents and incident reports from several countries (including the United States) as well as relevant photos, radar data, and material from private sources. She also interviewed official UFO investigators for several foreign governments along with military and civilian pilots, some of whom offered firsthand accounts reported in her book.
"These are people that you have to take seriously," Kean says.
Former United Airlines pilot Neil Daniels was one witness who shared his story with Kean. On March 12, 1977, Daniels was piloting a DC-10 on a routine flight from San Francisco to Boston. The aircraft was operating on autopilot when it suddenly started to turn left. Looking through the cockpit window, he and several other members of the United crew saw a brilliantly lit ball, roughly the size of their own plane, about 1,000 yards away. Daniels then noticed three of his compasses were pointing in different directions. After a few minutes, the glowing ball flew off at high speed. "Whatever it was, it wasn't an airplane," said Daniels, who passed away in May at his home in Los Altos, Calif. Air traffic controllers later reported they had not noticed any unusual radar traffic in the area, and the incident wasn't investigated further.
Even when government officials do try to examine a UFO sighting, they can be stymied by elusive—or vanishing—evidence. In Kean's book, a pilot in the shah-era Iranian air force describes a UFO encounter that Kean also found referenced in U.S. intelligence files. On Sept. 18, 1976, civilians and military officials at an air base near Tehran spotted a large diamond-shaped object with pulsating colored lights flying over the city in the late evening. Two fighter planes, including one piloted by the major who recounted the event, were scrambled to intercept the craft, which was also picked up on radar and described as being about the size of a 707 tanker jet. The major reported that, as he approached, the UFO seemed to emit a projectile. Believing it was a missile, the officer tried to return fire, but his weapons wouldn't respond. Though he said the "missile" appeared to land on the ground below, no evidence of it was found. The larger craft disappeared from the sky in an instant. A U.S. Defense Intelligence Agency review later that year called the incident "a classic which meets all the criteria necessary for a valid study of a UFO phenomenon."