For decades, marine biologists have tracked a lone whale in the North Pacific known as "52 Blue" because it calls at a frequency of 52 hertz — far higher than the great baleen whales it swims among — meaning that for a lifetime it has been calling out into the ocean in a voice that, as far as anyone can tell, no other whale has ever answered (opens in new tab)

In 1989, a network of underwater microphones picked up a sound in the North Pacific that nobody could explain. The microphones weren’t built to listen for whales. They were a Cold War system, installed by the U.S. Navy to track Soviet submarines. But the sound they caught wasn’t a submarine. It wasn’t mechanical at all. […]