'Perrier Ocean' Could Give Kick to Saturn Moon's Geysers

At least four distinct plumes of water ice spew out from the south polar region of Saturn's moon Enceladus in this dramatically illuminated image released by NASA on Oct. 1, 2010. The image was taken by the Cassini spacecraft on Dec. 25, 2009.

The mysterious icy jets erupting from Saturn's moon Enceladus may have their roots in a bubbly "Perrier ocean" flowing beneath the moon's frozen surface, a new study finds.

This salty subsurface sea could feed violent geysers on Enceladus, supplying them with water, gas, dust and heat before sinking back to the dark depths.

Matson discussed the Enceladus find at the American Astronomical Society's Division of Planetary Sciences meeting in Pasadena, Calif.

Mysterious geysers on an icy world

The ice geysers of Enceladus were first spotted in 2005 by NASA's Cassini spacecraft, which revealed jets of icy particles erupting from the moon's southern polar region. Enceladus is Saturn's sixth-largest moon.

The discovery jolted many astronomers — as did other evidence of a hot spot around Enceladus' south pole — showing that the small, frozen and presumably dead moon is geologically active.

More recent observations from Cassini have shown that the geysers are associated with Enceladus' "tiger stripes" — huge fissures in the moon's ice-covered surface.

Cassini has also found that the geysers contain water vapor, sodium salts, potassium salts and carbonates, suggesting that a sea of liquid water flows beneath the moon's icy crust.

The probe's observations revealed huge amounts of heat flowing through the tiger stripe region — about five times more heat per unit area than flows through Earth's geologic hot spot, Yellowstone National Park, scientists have said.

Such finds further intrigued scientists, but they didn't fully explain the fundamental nature of Enceladus' geysers or what was feeding them. The new results could help flesh out that explanation.

A heat-transferring sea

Matson and his colleagues came up with a computer model that accommodates much of what is known about the geysers of Enceladus. Their findings support the supposition that a salty sea flows under the moon's surface.

This ocean has gases dissolved in it, the theory goes. As the seawater flows up to and through the tiger stripe fissures, its pressure drops and the gases bubble up, Matson said — making the ocean fizzy, like Perrier. The relatively warm water and expanding gas feed the jets.

When the bubbles pop, they throw off a fine spray that contains salt and other materials, which Cassini spotted in Enceladus' plumes. Then the seawater, having dumped much of its warmth on the moon's surface ice, cools and sinks back through cracks, rejoining the ocean and its heat-transferring circulation system.

"Until now, how you got so much heat out was a big, big problem," Matson said.

The model doesn't require much dissolved gas in the "Perrier ocean" to work — only 1 or 2 percent, researchers said. And it explains the geyser phenomenon pretty well, including the ultimate source of some of the materials ejected in the plumes.

"A liquid ocean would be in contact with the rocky core" of Enceladus, said Linda Spilker of the Jet Propulsion Laboratory, Cassini deputy project scientist. As it flows past that core, the sea could pick up elements like sodium and potassium, she added.

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Michael was a science writer for the Idaho National Laboratory and has been an intern at Wired.com, The Salinas Californian newspaper, and the SLAC National Accelerator Laboratory. He has also worked as a herpetologist and wildlife biologist. He has a Ph.D. in evolutionary biology from the University of Sydney, Australia, a bachelor's degree from the University of Arizona, and a graduate certificate in science writing from the University of California, Santa Cruz.