Picture the absolute silence of an Ohio summer night in August 1977. Inside a cramped control room, astronomer Jerry Ehman is scanning through continuous line-printer paper from an old IBM 1130 computer connected to the "Big Ear" radio telescope. Looking at a sea of low numbers representing ambient cosmic static, he suddenly spots an impossible sequence of characters: 6EQUJ5. Ehman grabs a red pen, circles the sequence, and writes a single word in the margin: "Wow!" This marked the exact moment humanity intercepted a blindingly loud, narrow-band radio signal pouring in from the constellation Sagittarius. For exactly 72 seconds, it was as if a brilliant cosmic beacon was aimed directly at Earth before vanishing into permanent silence.

The SETI (Search for Extraterrestrial Intelligence) community had aligned  ...