An Ocean--and a Possible Home for Life--on Europa

Planetary scientists reported today that they have persuasive evidence for a deep ocean below the icy surface of Jupiter's moon Europa. New images from the Galileo spacecraft show features that bear an eerie resemblance to the ice floes of the Arctic Ocean, researchers told a NASA press conference today. An ocean, they noted, would give Europa a potential habitat for life. Some members of the Galileo team, however, aren't ready to take the plunge.

When Galileo began returning images of Europa late last year, planetary scientists realized that something has been disrupting large areas of the moon, squeezing up ridges, rifting open cracks, and crumpling some areas into thoroughly chaotic terrain. Last month at the Lunar and Planetary Science Conference in Houston, team member Clark Chapman of the Southwest Research Institute in Boulder, Colorado, argued that the striking dearth of meteorite craters on some parts of Europa implies that such reshaping of the surface is still happening.

Now Galileo has provided an even sharper view of the surface, convincing several researchers that a thin layer of ice floating on liquid water is the best explanation for this jumbled terrain. The new images reveal what seem to be kilometers-long slabs of ice obviously broken off and drifting in a "sea" of small bits, say these researchers. "These are icebergs," says Galileo team member Paul Geissler of the University of Arizona. He and fellow team member Michael Carr of the U.S. Geological Survey in Menlo Park, California, argue that the circulation of a warm ocean has partially melted the ice crust and dragged the "icebergs" around. Geissler adds that a red-brown coloration in the disrupted areas "marks the waterline of a murky, possibly muddy ocean not too far below the surface," perhaps a couple of kilometers down.

"It's a bold hypothesis that probably has some staying power," says team member Robert Sullivan of Arizona State University, "but there's room there for some surprises." Team member Robert Pappalardo of Brown University agrees: "I don't think we have proof of an ocean." He says that ice could have moved around on top of ductile ice instead of an ocean.