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  • 5/16/2007

Saturn moon gushing geysers revealed

The moon

Mysterious vapor geysers on a Saturn moon may result from massive cracks in ice cover opening and closing under the gravitational sway of the satellite"s lopsided orbit, according to a study released Wednesday.

Scientists have been baffled since the discovery two years ago of gushing eruptions along parallel fault lines nicknamed "Tiger Stripes" at the south pole of Enceladus, one of only four planetary bodies in our solar system, including Earth, known to make such showy displays.

The vapor gesyers seemed to provide evidence of warm water not far under the surface, but that did not square with temperatures of minus 193 degrees celsius (minus 315 degrees fahrenheit) and ice estimated to be several kilometers (miles) thick.

A team of researchers led by Francis Nimmo at the University of California, however, have proposed another explanation: the amount of heat generated by the chaffing of massive tectonic ice plates against each other would account for the vapor plumes, as well as other observed phenomena.

They tested their hypothesis with computer models that correctly predicted where, along the huge cracks in the ice surface, the most heat and therefore the largest geysers would occur.

The "Tiger Stripe" fault lines average 130 kilometers (80 miles) in length, and two kilometers across.

Driving the whole process is the moon"s elliptical orbit, which brings it closer to Saturn at higher speeds, and then takes it further away, with a corresponding change in the force of the planet"s gravitational pull.

"It"s getting squeezed and stretched as it goes around Saturn, and those tidal forces cause the fault lines to move back and forth," Nimmo explained in a statement.

The study, published in the British journal Nature, also concluded that Enceladus does have a liquid ocean buried kilometers beneath its surface, making the movement of its enormous ice plates possible.

If the ice shell were sitting directly on top of the moon"s rocky exterior, Nimmo said, the gravitational pull would not produce enough movement in the faults to generate heat.

The researchers also found evidence that the ice covering the tiny moon, some 500 kilometers in diameter, is at least five kilometers thick, probably several times thicker.

In a second study, also published in Nature, another team of scientists led by Terry Hurford of the Goddard space flight center explain how cracks in the ice surface open and close under Saturn"s gravitational pull.

Enceladus has intrigued scientists since the discovery more than a year ago of the geysers by NASA"s Cassini spacecraft, part of a joint space mission involving NASA, the European space agency, and the Italian space agency.

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