In 1967, Cambridge astronomers detected a strange radio signal coming from the distant Vulpecula constellation. Regular, pulsing signals were beaming across the galaxy, and there was a very real possibility that the signals were coming from an artificial source. The discovery sparked much debate — at the time, there was no protocol for responding to extra-terrestrial contact. How should we reply? What if the signal is from aliens looking for a planet to occupy — shouldn't there be an international discussion?

For the first time since the discovery, the full story of the detection, reaction to, and eventual understanding of the signals has been revealed in a paper titled The SETI Episode in the 1967 Discovery of Pulsars. As we now know, the signals came from pulsars — highly magnetized, rotating stars — but the episode influenced the eventual development of the "discovery protocol:" a code of conduct for replying to extra-terrestrial messages.