For decades, scientists have been actively searching for signs of extraterrestrial life. Fromradio waves to laser flashes and infrared heat signatures, the hunt for alien technosignatures has captivated both researchers and the public.

The first sign of possible extraterrestrials detected in the cosmos didn't come in the form of little green aliens flying around in saucer-shaped spacecraft. In fact, the life that could be – emphasis on the could be – thriving on a distant ocean ...