Okay, we’re cheating a bit here, but Lake Vostok in Antarctica certainly qualifies as the most unearthly body of water on Earth.
The largest of Antarctica’s subterranean lakes, Vostok sits some 12,370 feet (3,770 meters) beneath the East Antarctic Ice Sheet. It measures 162 miles long (260 km) and 30 miles wide (50 km), and has a maximum depth around 1,640 feet (500 meters). Incredibly, the lake sits beneath 2.5 miles (4 km) of ice.
Lake Vostok formed around 14 million years ago, and its water has been isolated from the rest of the world for around 1 million years. Vostok thus offers a unique environment for scientists studying ancient ecosystems, as this body of water could contain species never seen before (cue ominous horror movie music). What’s more, Lake Vostok could be a good analog for Europa and Enceladus, which also feature bodies of water beneath an icy crust.