An Icy World Looks Livelier

Washington--The latest images of Jupiter's moon Europa, released here today at a NASA press conference, have planetary geologists in a tither. To team members poring over images returned by the Galileo spacecraft, the wild jumble of ridges, grooves, pits, ice flows, and chaotic terrain shows more signs that heat forged Europa's icy surface. But just how hot it could become below that surface is the crucial unknown in the mystery of whether Europa has ever supported elementary life.

"These new images demonstrate that there was enough heat to drive [ice] flows on the surface," says Galileo imaging team member Ronald Greeley of Arizona State University. "Europa thus has a high potential" as a place where life could begin, he says.

In images showing detail as much as 20 times finer than ones previously sent back by Galileo, two new features are further persuading space scientists that at some point Europa was relatively warm. Greeley points to several features in the accompanying image that he suspects depict various stages in the process of plumes of warm ice or icy mush rising toward the surface. The plume first bulges the surface (lower left of bottom image block) and cracks it (middle of top block). Then some unearthly geologic process takes over in which the broken terrain collapses into a chaotic jumble of ice blocks (right side of middle image blocks). Greeley speculates that sublimation of small amounts of ammonia or methane ice from the water ice robs the terrain of the glue that holds it together, and it crumbles. In other images shown on the Galileo Web site, rising water or icy mush appears to have burst through the surface like an ice volcano and flowed as 100-meter-thick lobes of ice for hundreds of kilometers.

So Europa has been warm, but planetary scientists must now try to decide whether these signs of warmth mean an ocean lurks beneath the surface. An ocean may have existed in the moon's youth and frozen solid since, squeezing out these dribbles of ice with its last gasp. Or, it could still be warm, liquid, and teeming with life. Galileo's future close encounters with Europa may tell.