On 15 August 1977, the Big Ear radio telescope at detected an anomalously strong radio signal from deep space. An alphanumeric representation of the signal’s intensity “6EQUJ5”,a spike so remarkable that astronomer Jerry Ehman circled it and wrote “Wow!” in the margin.

The signal came from the direction of the constellation Sagittarius,with no known Earth-originating source. The nearest star in that region is 122 light years away. To this day, scientists haven’t detected it again. Its origin remains a mystery.