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Hidden sea on a Saturn moon? New evidence says yes.

Satellite Cassini flew through geyser plumes spouting from Enceladus and gathered ice crystals. These crystals are salt-rich, suggesting that a hidden salty sea lurks beneath Enceladus's icy cap.

By Staff writer / June 22, 2011

The geysers emerging from the southern pole of Enceladus, captured here by Cassini in 2010, suggest that the icy moon have hidden liquid depths.

SSI/JPL/NASA

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Spectacular geysers of ice crystals that erupt from Saturn's moon Enceladus – and that formed Saturn's diaphanous E-ring – likely come from a subsurface sea reminiscent of Jules Verne's "Journey to the Center of the Earth."

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Moreover, the geysers appear to be driven by a mysterious heat source unlike anything yet seen in the solar system.

Those are the implications of a new study of the geysers' plumes. The study will appear in Thursday's issue of the journal Nature.

If the conclusions hold up to further scrutiny, they also imply that ice-encrusted Enceladus – far from the sun's "habitable zone" – could harbor a subsurface environment hospitable to simple forms of life.

Although the notion of a under-ice sea on Enceladus isn't new, until now the evidence in hand has allowed for an explanation for the ice plumes that doesn't require presence of liquid water, explains Sascha Kempf, a planetary scientist at the University of Colorado at Boulder and a member of the team reporting the results.

But by analyzing ice samples from the plumes, gathered by NASA's Cassini orbiter, the research team determined that 99 percent of the mass of the plumes is accounted for by salt-rich ices.

The simplest way to pick up the salts is for water to leach them out of rock over long periods of time. It's a process similar to the one that salts Earth's oceans.

The new results indicate that, despite its sound basis in physics, the "dry" solution to the geyser puzzle "is now off the table," Dr. Kempf says. "Nature did not choose that option."

The results conjure up an image of a sea in a vast subsurface cavern, Kempf acknowledges, although he adds that the team doesn't know whether the sea is global or local to the south pole.

According to the model proposed by the research team, water boils off the top of the subsurface sea, into the near-vacuum environment. As the water bubbles burst, the spray freezes into tiny crystals that get swept along with gases, up through fissures in the moon's ice crust.

The new results resonate with at least one scientist who help craft the "dry" explanation for the plumes, which appeared in a 2006 research paper in the journal Science. "I prefer this straightforward explanation," offers John Spencer, a planetary scientist at the Southwest Research Institute in Boulder, Colo. "The warm temperatures implied by liquid water will provide plenty of pressure to drive the plumes," he writes in an email exchange.

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