The brief but intense signal, detected by radio telescopes in Western Australia, lasted only a fraction of a second yet became the brightest object in the sky, momentarily outshining entire galaxies and stars. The source of this unexpected burst was Relay 2, a communications satellite launched by NASA in 1964. After both of its transmitters failed in 1967, the satellite had been silent and declared defunct until now. Experts believe the signal wasn't deliberately transmitted by the satellite, but was triggered by an external event. One possibility is an electrostatic discharge: a sudden release of electrical energy, similar to a...