Oceans were long thought to exist in all corners of the Solar System, from carbonated seas percolating beneath the clouds of Venus to features on the Moon's surface given names such as "the Bay of Rainbows" and the "Ocean of Storms." With the advent of modern telescopes and spacecraft exploration these ancient concepts of planetary seas have, for the most part, evaporated. But they have been replaced by the reality of something even more exotic. For...