New Look at Geysers on Saturn Moon Chills Chances of Life

Brian Handwerk
for National Geographic News
May 16, 2007
Scientists may have found the source of towering geysers on Saturn's moon Enceladus—but the discovery could be a setback for hopes of life on the distant satellite.

Enceladus's plumes of icy water vapor have intrigued observers since they were spotted by NASA's Cassini spacecraft in 2006.

Some have theorized that the geysers are caused by underground liquid water that freezes instantly when it is jettisoned into space.

If reservoirs of subsurface water exist on Enceladus, so might primitive life forms.

But two papers published in the May 17 issue of the journal Nature suggest that the geysers are caused by the friction between massive plates of ice.

The new studies suggest that ice plates tens of kilometers deep periodically grind together at fault lines on the moon's surface.

The heat created by this friction may turn the ice directly into vapor, thereby producing the geysers.

"The two sides are rubbing backwards and forwards against each other," said Francis Nimmo, a planetary scientist at the University of California, Santa Cruz, and lead author of one study.

"Just like when you rub your hands together, you get heat—that is how we think the ice is being heated up."

Saturn's Internal Ocean

The plates of ice may be moving because of the tug from Saturn's gravitational pull. (See pictures of Saturn from Cassini.)

"Enceladus's orbit isn't quite circular," Nimmo said. "As it goes around Saturn the distance between them is changing, so Saturn's gravitational attraction is changing."

A second Nature study suggests that Enceladus's orbit, and corresponding tides on Saturn, could make the geyser eruptions regular and predictable.

Though the ice-friction theory could strike a blow to hopes for liquid water near the moon's surface, the theory still proposes that liquid water exist somewhere inside Enceladus.

"We suggest that you need to have an ocean somewhere down there," Nimmo explained.

"If you didn't, the ice shell would be stuck to the rigid rock interior [and would not move]. If there is an ocean below and the ice shell is floating, it could move to produce the friction and heating."

Amy Simon-Miller, an astrophysicist at NASA's Goddard Space Flight Center in Maryland, says it may be some time before Enceladus's true nature is known.

"The details of the internal structure may or may not be discernable from these predictions," she cautioned, "because Cassini is just not optimized for studying Enceladus.

"We probably won't get a good sense of the interior until we can send [a] dedicated mission."

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