There have been a number of reported objects that were once thought to exist by astronomers, but which later 'vanished'. For instance, two days before the March 29, 1974, Mariner 10 flyby of Mercury, one instument began registering bright, extreme ultraviolent emissions that had "no right to be there." The next day, the emissions were gone. Three days later, they reappeared, apparently emanating from an "object" that seemingly detached itself from Mercury. The astronomers first thought they had seen a star. But, they had seen the emissions in two quite different directions, and every astronomer knew that these extreme UV wavelengths couldn't penetrate very far through the interstellar medium. This suggested that the object must be relatively close. Did Mercury have a moon?