The Wow! Signal (1977)

Detected by Ohio State University's Big Ear radio telescope, the Wow! Signal remains one of astronomy's greatest unsolved mysteries. Lasting 72 seconds, this powerful narrowband radio burst matched expected characteristics of an extraterrestrial transmission. Originating near the Sagittarius constellation, it was never detected again despite repeated searches. While natural explanations (like comet emissions) have been proposed, none fully explain its intensity and frequency. Decades later, the Wow! Signal continues to fuel debates about intelligent alien life—making it the most compelling (and frustrating) candidate for a potential extraterrestrial message.