Life on Europa might be detectable

By DAN WHIPPLE, UPI Science News  |  Oct. 30, 2002 at 12:30 PM
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DENVER, Oct. 30 (UPI) -- Only a mile or two below the surface of Jupiter's moon Europa, circulating pockets of warm ocean water could be bringing living organisms -- if they exist there -- close enough to the surface that earthlings someday might get a look a them, an astrophysical researcher reported Wednesday.

"Much of Europa's subsurface is warm, and closer to the surface than thought," Robert Pappalardo, University of Colorado astrophysical and planetary sciences assistant professor, told United Press International.

Jupiter's fourth-largest moon, Europa is covered by a shell of very hard ice and the thickness of that hard shell is the topic of vigorous debate in modern astrophysics. Pappalardo said his model of Europa's geology suggests the ice covering is only about 2 kilometers (1.24 miles) thick, as opposed to previous models that predicted it is about 6 kilometers (3.72 miles) thick.

According to relatively new information on how ice flows, Pappalardo said there might be warm pockets of water flowing like a "lava lamp" -- the novelty item featuring illuminated and meandering blobs of mineral oil -- under the out layer of ice. These pockets, existing at temperatures of about 240 degrees Kelvin (about -20 degrees Fahrenheit), might carry organic material from the ocean thought to lie beneath Europa's ice encrusted surface.

Amy Barr, a UC graduate student, has developed a computer-generated movie that shows the large pockets of warmer ice and water circulating close to the surface.

The entire ice covering of Europa -- the thick cap ice, as well as less dense material below it -- is estimated to be about 20 kilometers (12.5 miles) thick. In Pappalardo's model, however, "just a mile or two below the surface, the conditions may be warm enough to allow organism to survive the journey."

If there are any living organisms in Europa's ocean, they might survive in the relatively warmer pockets of water that circulate from lower down toward the moon's core then up toward the ice cap. It means if a space probe is sent to Europa, "It is a lot easier to get through 2 kilometers of ice than five," Pappalardo said.

"In Arctic sea ice, there are dormant organisms in brine sea ice at minus 15 Centigrade (5 degrees Fahrenheit)," he said, which is at least in the range of the temperatures his model is predicting for Europa. The model also predicts the pattern of the observed surface features on Europa -- a wilderness of domes, craters, ridges, cracks and other surface features. By allowing the ice to move around, the model also could explain "chaos areas," on the moon's surface, he said.

Pappalardo is working with Massachusetts Institute of Technology acoustical oceanographer Nick Makris on a plan to land a single geophone listening device on the moon's surface. By applying the technique, already used on Arctic sea ice, Makris said they could determine the depth of the ice and the extent of any potential ocean underneath.

Pappalardo and Makris are presenting back-to-back papers at the Geological Society of America's annual meeting.

Not everyone agrees with Pappalardo's estimates, however. In a November 2001 article in the journal Science, Elizabeth P. Turtle and Elisabetta Pierazzo of the University of Arizona Lunar and Planetary Laboratory used an analysis of craters to estimate the surface's ability to resist impact from meteors. They concluded the ice cap was more than 3 or 4 kilometers (1.86 miles or 2.48 miles) thick.

"It's only been since (the Galileo space probe has) been getting images that we can talk coherently about the geology," said Paul Schenk, a planetary geologist at Houston's Lunar and Planetary Institute, who has studied Europa extensively. "Geologists have been taking a look at it and going back and forth about how thick the ice is. It is hard to really get a good answer from geology alone, by mapping or geological analyses," Schenk told UPI.

Nevertheless, Schenk said, Pappalardo's "lava lamp" concept sounds plausible. "I think he can make a fairly good case that is probably what's happening," he said. "These things that we see on the surface look very much like what you would see in the case of what he's proposing."

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