May 17, 2007 — Scientists have a new theory to explain the ice-spewing geysers on Saturn's moon Enceladus, which if correct, could dash suspicions of liquid water near the surface of the ice-encrusted world.
Beneath the smooth exterior, scientists suspect Enceladus is a tortured place, with a deep underground ocean that is constantly pushed and pulled by gravitational forces from Saturn and nearby sister moons.
The motion causes the moon's huge ice sheets to grind together, producing fault lines on the surface which have been observed by the Cassini probe, according to Francis Nimmo, a planetary scientist with the University of California in Santa Cruz and the lead author of a paper appearing in this week's issue of Nature.
"It's getting squeezed and stretched as it goes around Saturn, and those tidal forces cause the faults to move back and forth," Nimmo said.
The lines, which resemble tiger strips, are likely places where Enceladus' ice sheets are opening and closing. Frictional heating also may be causing water vapor to burst out from the fault lines, Nimmo said.
"Different stripes open at different times in the orbit," said Terry Hurford, with NASA's Goddard Space Flight Center, Greenbelt, Md.
The heat generated by the tidal forces is so intense that Enceladus' deep-seated water could instantly transform from solid to gas, a process known as sublimation.
Previously, researchers believed vapor plumes, photographed by Cassini as it flew by Enceladus, stemmed from a pool of liquid water sitting just beneath the surface.
"Assuming they erupt as soon as they open, exposing liquid water to the vacuum of space, we can predict which stripes will be erupting at certain times in the orbit," said Hurford, lead author of a related paper in Nature.
The new model does not require the presence of liquid water near the surface of Enceladus, said Robert Pappalardo, with NASA's Jet Propulsion Laboratory in Pasadena, Calif.
It does, however, presume an underground ocean. As Nimmo explained, if the ice shell rested directly on the moon's rocky interior, tidal forces would not produce enough movement in the faults to generate heat.
The new study suggest Enceladus' ocean is much, much deeper than previously believed and is buried beneath an ice sheet suspected to be at least three miles thick and more likely several times that depth.
