A post from the science website Earthsky revisits the "loneliest whale in the world," an unknown whale that the Navy has tracked since 1992 with submarine monitoring equipment -- identifiable by its song sung at a frequency of 52 Hertz that's not shared with any other known whale on earth.

The naval monitoring has tracked the whale all around the waters of the Pacific Ocean lining the West Coast of the U.S. and Canada, even approaching Alaska's Aleutian Islands. According to this map of the whale's migration, the Aleutians and Kodiak Island appear to be the closest to shore the whale ever came over the course of 10 years.

The whale, simply dubbed the 52-Hertz whale, has been on biologists' radars since the mid-2000s for its uniqueness. The typical whale call operates at a much lower frequency -- between 15 and 25 Hertz, according to Earthsky. For comparison, that's "just above the lowest note on a tuba," according to a 2004 New York Times article on the whale. Meanwhile, Blue whale songs have been shown to be lowering in frequency over time, pushing them even farther from the 52-Hertz whale.

The NOAA has a collection of whale calls that includes the 52-Hertz whale. The actual frequencies are much lower than the recordings, which have been sped up for easier listening. For comparison, here's a humpback whale recorded in Alaska waters.

And here's the cry of the lonely 52-Hertz whale, which no other whale can return -- as if whale songs weren't mournful enough.

Additionally, the 52-Hertz whale doesn't follow a migration pattern of any other known filter feeding (or baleen) whale. Part of the gray whale's migration path covers the same turf as the 52-Hertz whale, but gray whales travel much further north, to the Bering Strait, in the summer months and down the Baja Peninsula in Mexico during winter.

All of this, of course, has led to speculation over whether the whale is a one-of-a-kind anomaly. The team of scientists that initially reported the discovery of the 52-Hertz whale concluded that it was likely not a new species or the sole member of an unknown species. But this hasn't satisfied some in the less-scientific community, who have bandied about theories that include a hybrid of two other existing whale species or even the last surviving member of another, unknown species.

Whatever the case, next time you're whale-watching near Kodiak or the Aleutians during the annual northern migration, maybe keep an eye out for one lonely whale, breaching and diving, singing a song that only it knows.