The data, which was collected by Galileos magnetic-field-detecting instruments when the spacecraft flew close to the icy moon, showed that there is an electrically charged layer of some substance stirring possibly as close as 4.7 miles (7.5 kilometers) below the moons ice crust. Planetary scientists say the most likely explanation for the data is a liquid-water ocean similar to oceans found on Earth a possibility that has extraterrestrial life-seekers reeling with excitement.

Europa may be frozen solid on the surface, but planetary scientists have known for years that the Europan interior is heated by tidal flexing, a process fueled by the gravitational forces felt from the enormous pull of Jupiter and other neighboring moons. This heating, though not as apparent as on Europas sister moon Io, appears to cause inner layers of Europa to remain liquefied rather than solid.

Now, after analyzing their most recent data on Europas interior, researchers at the University of California at Los Angeles have concluded that Europas magnetic field oscillates or flip-flops, a property that could only be explained by a layer of some electrically conductive material. Though the possibility of some other conductive material, such as a carbon-rich material like graphite, is not completely out of the question, scientists say that liquid water or possibly even slushy watery ice is the most logical answer.

"One can more easily imagine that theres a salty ocean than another exotic material that could give you this kind of conductivity," said Krishan Khurana, one of the lead investigators on this latest Europa find. "In terms of plausibility, an ocean is the most likely scenario."

Khurana and his colleagues first realized they might be looking at the possibility of a global Europan ocean two years ago, when they stumbled on an odd signature in Europas magnetic field during an earlier Galileo flyby. Though the one pass provided only a brief glimpse, it appeared that Europas magnetic field might be flipping regularly due to the influences of planet Jupiters strong magnetic field an occurrence which could only be explained by a thick conductive layer several miles (kilometers) below the surface.

The question of a global ocean has many in the scientific community wondering whether Europa may be the most likely body in the solar system to support life, perhaps in the form of small single- or multi-celled organisms. But others caution that though the prospects are stirring, much more in the way of research has yet to be carried out before any firm conclusions about life may be drawn.

"We can say two things about requirements for life on Europa: One, that theres water, and two, that theres a source of heat," said Khurana. "But life also requires many other prerequisites the right mix of chemicals, and the right type of environmental conditions. Right now we can say nothing about [life]; others will have to come out with answers as to that possibility."

Researchers hope to literally test out the waters on subsequent missions to icy Europa, including the Europa Orbiter which is already in the works for launch in 2006 and possibly even a future landing mission. "Were all extremely pleased that there is going to be a follow-up," said Khurana of the Orbiter. The Europa Orbiter and subsequent missions will search not only for signatures of life, but will research the inner workings of Europa how its crust is formed, what its inner layers look like, and what the Jovian moon is composed of.