There's Some Motion in the Ocean

When you're tooling out around Saturn, some 1.46 billion kilometers (900 million miles or so) from the sun, things are pretty cold. So if one of Saturn's moons has water on it, you'd expect that water to be ice.

Then one day in 2005, the Cassini probe flew by Enceladus -- the sixth-largest of Saturn's satellites -- and found something very interesting: It seemed to have sprung a leak. The four streaks spouting from the south pole of the moon in the photo here are actually gigantic plumes of water, shooting into space. Scientists found this out in 2008 after Cassini gathered and analyzed the ice crystals made by the plumes after they had refrozen. In fact, they're salty, which means water is liquid on Enceladus long enough to dissolve minerals into it, like in our oceans.

The problem is that Enceladus is too small and too far from the sun to maintain liquid water. A moon or planet has to be within a certain range of its sun or be large enough to generate enough of its own heat to keep chemicals and compounds from freezing. We're close enough to the sun, for example, that many substances are liquids at our average temperatures. Saturn and Jupiter are so large that, even though they are much farther away from the sun than we are, they generate enough internal heat to maintain the gaseous or liquid nature of the different substances that make them up.

Soo, how does this dinky little moon manage to have water, and in enough abundance that scientists think it might actually be possible for it to support some kind of life? Originally, scientists figured that the stress of tides generated during Enceladus' orbit of Saturn would generate heat. Enceladus is about three-fifths as far from Saturn as our moon is from us. Saturn is much, much larger than the earth, so its gravity creates tidal stresses much more powerful. The way those stresses pull the moon this way and that could provide enough friction within its own surface to heat the water to a liquid point. But the computer models didn't quite work, so they started looking for other factors, and they found a wobble.

The wobble not only generates more heat by making the gravitational stress on Enceladus stronger and increasing friction, it also shows scientists why the icy surface of the moon cracks from time to time and allows the giant streams of water to erupt into space. Coincidentally, in Greek mythology Enceladus was one of the Gigantes defeated by the Olympians, and was imprisoned by being buried under what is now Mt. Etna in Sicily. The volcano's fiery eruptions are supposed to be his breath and the tremors which shake the island from time to time were thought to be caused by Enceladus rolling to ease the pain from his wounds.

Without exploring Enceladus, there's no way to see if there really is life in its oceans, or if the conditions are right but nobody's shown up yet. It may be that closer exploration of the moon shows the water isn't trapped in caves or a part of an ocean but something else entirely.

Either way, whatever exploration takes place is likely to produce some spectacular scenery. The Cassini probe showed some of the plumes extended as much as 500 kilometers (about 300 miles) from the surface of the moon, meaning they are as "tall" as the moon itself is "wide." They don't show up that big in the photo because of the distance Cassini is from the moon when it was taken. Maybe in a hundred years or so, Niagara Falls will take a backseat as a honeymoon destination to the Fountains of Enceladus. And even if they don't, "Fountains of Enceladus" sounds like an awesome name for a science-fiction novel. I would have said, in my best Dave Barry fashion, a good name for a rock band, but Fountains of Wayne might not have thought that was so funny.