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By Jeffrey Kluger
NASA / JPL-Caltech / Space Science Institute
It's hard enough for kids to remember all the known oceans and seas — Atlantic, Pacific, Indian, Norwegian, Barents — and now they can add one more to the list: the Enceladan Ocean. The name is lovely, and the place is nifty, but there's not much chance of visiting it soon. It's located on Enceladus, one of Saturn's 66 known moons. While Enceladus has been familiar to us since it was first spotted in 1789, the discovery of its ocean, courtesy of the venerable Cassini spacecraft, is a whole new and possibly game-changing thing.
Enceladus has always been thought of as one of the more remarkable members of Saturn's marble bag of satellites. For one thing, it's dazzlingly bright. The percentage of sunlight that a body in the solar system reflects back is known as its albedo, and it's determined mostly by the color of the body's ground cover. For all the silvery brilliance of a full moon on a cloudless night, the albedo of our own drab satellite is a muddy 12%, owing mostly to the gray dust that covers it. The albedo of Enceladus, on the other hand, approaches a mirror-like 100%.
Such a high percentage likely means the surface is covered with ice crystals — and, what's more, that those crystals get regularly replenished. Consider how grubby and gray a fresh snowfall becomes after just a couple of days of splashing road slush and tromping people. Now imagine how a moon would look after a few billion years of cosmic bombardment by incoming meteors.
When the Voyager probes barnstormed Enceladus in 1982, they found that the moon is indeed covered in ice and being constantly repaved. Vast valleys and basins were filled with fresh, white cosmic snow. Craters were cut clean in half, with one side remaining visible and the other covered over. Most remarkably, Enceladus orbits within Saturn's E ring — the widest of the planet's bands — and just behind the moon is a visible bulge in the ring, the result of the sparkly exhaust from ice volcanoes that trails Enceladus like smoke from a steamship. It's that cryovolcanism that's responsible for the regular repaving.
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