Locked under ice, the hidden oceans of Europa, one of Jupiter's moons, may be tumultuous rather than placid, a new study says.
Such oceanic unrest translates into a higher potential for life.
(Related: "Jupiter Moon May Have Life -- Experts Urge a Mission" [March 23, 2005].)
Robert Tyler, an oceanographer from the University of Washington, has used computer simulations to show that Jupiter's effects on its moon Europa may work differently than scientists once thought.
Rather than just stressing the moon's solid parts—squeezing its rocks and flexing a global shell of ice—Jupiter's relentless tugging may also generate huge planetary waves in Europa's submerged ocean.
These waves could be the primary vehicles for distributing energy, as heat, across Europa. The new theory counters a widely held impression that Europa's ocean is calm.
"Suddenly, now our whole conception has to be one of very energetic oceans sloshing around under this ice," Tyler said.
"I consider the specific case of Europa, but the general results apply equally to other moons with suspected oceans," he wrote in his paper, which appears in the journal Nature this week. Those moons include Jupiter's Callisto and Ganymede, along with Saturn's Enceladus and Titan.
Heat seekers
Europa travels a slightly oblong orbit around Jupiter. When it reaches the sharper curves at either end, the moon wobbles to release pent-up energy, which translates into tides.
(See an image of Jupiter, Io, and Europa.)
Tyler is the first to suggest that Europa, like Earth, may dissipate most of its tidal stresses in oceanic waves.
David Stevenson, a planetary geologist at the California Institute of Technology in Pasadena, called the new theory "an interesting possibility" in an email.
"But at the end of it all, what I see here is a possibility that could well be (and most likely is) less important than the conventional story," he wrote.
"It would of course be more exciting and relevant if we were at a loss to understand how dissipation takes place at all. But that's not the situation."
Stuff of Life
NASA's Galileo spacecraft investigated Jupiter and its moons between 1989 and 2003, and sent data indicating that Europa's ocean could be salt water.
"That doesn't necessarily mean sodium chloride [salt]," Tyler said. "It could be magnesium sulfate, basically an Epsom bath."
Jeff Kargel, a geologist affiliated with the University of Arizona in Tucson, suggested in the late 1990s that Europa's salts may help it host life.
Kargel pointed out that many unknowns remain with respect to the composition and thickness of the liquid on Europa and its overlying ice.
"The big thing is to have liquid water—and to the extent that this new paper adds an energy source—all the better for life's prospects."
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