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Europa: secret lakes could fuel life on Jupiter moon

New research suggests that lakes of liquid water could be buried in the icy crust of Europa, a moon of Jupiter. The processes that create the lakes could also provide nutrients crucial for life on Europa, the scientists say.

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The team suggests that plumes of warmer water, heated by Europa's core, migrate up through the thick icy crust until they reach a "sweet spot" where a combination of pressure, temperature, and the composition of the ices allows a subsurface lake to form. Since liquid water takes up less volume than water ice, the icy lid on top of the lake begins to crack and collapse in a kind of frigid sink hole. The surface ice breaks into chunks in the process. As it does, some of it overturns, mixing the potential nutrients into the water below.

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That explains the depressions. But what about the domes?

Over time, the lake refreezes and expands. This pushes remaining large ice blocks upward. The brine surrounding the blocks also refreezes, expanding as it does, adding to the dome.

One of the features, Thera Macula, is a depression, suggesting that a Great Lakes-scale body of water some two miles below currently is sculpting the surface, the team says. A dome feature, known as Conamara Chaos, represents the end of another lake's thaw-freeze process.

Over time, researchers have debated whether the icy shell covering Europa is thin or thick – thick roughly defined as more than six miles top to bottom. But neither camp can adequately explain how the chaos terrain forms, the team posits.

The team's new explanation "is a really interesting half-way point that is much more realistic," says Geoffrey Collins, a planetary scientist at Wheaton College in Norton, Mass. "It's not just 'only liquid down here and only ice up there.' There are perched lakes or slushy areas in the ice shell that may be having a huge effect on the surface geology," he says.

The thin-thick argument is of interest to astrobiologists, says Dr. Collins. If the crust is thick – say, 18 miles or so – that would leave little hope of ever being able to sample the ocean and check for signs of life. If it's thin, hope would spring eternal for sending a robotic mission to study what's beneath.

The new explanation leaves open the possibility for exploring potentially habitable environments even if the icy shell turns out to be a thick one.

Collins, however, is less convinced that the process can bring nutrients in the upper crust down to any hidden ocean. In the scenario the team lays out, the heat plumes that form the lakes – and the lakes themselves – don't come into contact with an ocean at any depth below the surface.

But Curt Niebur, NASA's program scientist for the outer planets, explains that it's possible the overturning ice can transfer any potential nutrients to the water or slush below. That leaves the enriched material free to migrate back down through cracks in the ice.

These ideas require missions to Europa to test them, researchers acknowledge.

Even so, "I'm really excited" about the team's proposed solution to the chaos terrain conundrum, Collins says. Thick shell or thin, if the presence of the lakes can be verified, they could be "interesting, accessible bodies of liquid water."

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