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Saturn moon Titan's thick shell suggests bizarre interior

Scientists have found that the tough shell of Saturn's largest moon Titan is stronger than previously thought and hints at an unusual interior.

By Charles Q. / August 28, 2013

Saturn's moon Titan, seen passing in front of the planet, has a tough, icy shell that indicates its strange insides, according to a new paper published in Nature.



The tough icy shell of Saturn's largest moon Titan is apparently far stronger than previously thought, researchers say.

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These surprising new findings add to hints Titan possesses an extraordinarily bizarre interior, scientists added.

Past research suggested Titan has an ocean hidden under its outer icy shell 30 to 120 miles (50 to 200 kilometers) thick. Investigators aim to explore this underground ocean in the hopes of finding alien life on Titan, since virtually wherever there is water on Earth, there is life. [See more photos of Titan, Saturn's largest moon]

To learn more about Titan's icy shell, planetary scientist Doug Hemingway at the University of California, Santa Cruz, analyzed the Cassini probe's scans of Titan's gravity field. The strength of the gravitational pull any point on a surface exerts depends on the amount of mass underneath it. The stronger the pull, the more the mass.

The researchers then compared these gravity results with the structure of Titan's surface. They expected that regions of high elevation would have the strongest gravitational pull, since one might suppose they had extra matter underneath them. Conversely, they expected regions of low elevation would have the weakest gravitational pull.

What the investigators discovered shocked them. The regions of high elevation on Titan had the weakest gravitational pull.

"It was very surprising to see that," Hemingway told "We assumed at first that we got things wrong, that we were seeing the data backwards, but after we ran out of options to make that finding go away, we came up with a model that explains these observations." 

To explain these gravity anomalies, Hemingway said to imagine mountains on Titan having roots. "It's like how most of an iceberg actually lies submerged underwater," he said. "If that root is really big, bigger than normal, it would displace water underneath it."

Ice has a lower density than water — a chunk of ice weighs less than a similar volume of water. These high-elevation areas on Titan apparently have roots large enough to displace a lot of water under them, meaning they exert a weaker gravitational pull.

Ice is buoyant in water. "In order to essentially hold these big icebergs down and keep them from bobbing up, that means Titan's shell has to be extremely rigid," Hemingway said.

It remains uncertain what makes Titan's shell this rigid. The ice might possess cage-like molecules known as clathrates that could make it stiffer. Also, "if the ocean underneath the shell is colder than before thought, that could make the ice shell thicker and thus more rigid," Hemingway said.

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