The following recounts an incident in 2004 that advocates of research into U.F.O.s have said is the kind of event worthy of more investigation, and that was studied by a Pentagon program that investigated U.F.O.s. Experts caution that earthly explanations often exist for such incidents, and that not knowing the explanation does not mean that the event has interstellar origins. Cmdr. David Fravor and Lt. Cmdr. Jim Slaight were on a routine training mission 100 miles out into the Pacific when the radio in each of their F/A-18F Super Hornets crackled: An operations officer aboard the U.S.S. Princeton, a Navy...