"We realize that this is a radical conclusion - that we may have evidence for liquid water within a body so small and so cold," said Carolyn Porco, Cassini imaging team leader at the Space Science Institute in Boulder.

"However, if we are right, we have significantly broadened the diversity of solar system environments where we might possibly have conditions suitable for living organisms � it doesn't get any more exciting than this."

In three separate articles appearing in the March 10 issue of the journal Science, Porco and colleagues said high-resolution images of Enceladus show icy jets rising from the surface and towering plumes ejecting huge quantities of particles at high speed.

She said the team studied several computer models that might explain the process, but they abandoned the idea the particles are produced or blown off the surface by vapor created when water ice converts to a gas.

"We haven't found water, per se - we've found evidence of water, and our best models right now are those that suggest that there's pockets of liquid water under the surface, and what we're seeing in these jets are like the equivalent of Old Faithful, in Yellowstone (National Park in Wyoming), they're geysers that are erupting out of pockets of water."

Instead, she said, the evidence points to jets that might be erupting from near-surface pockets of liquid water - above 0 degrees Celsius (32 degrees Fahrenheit � just like colder versions of the Old Faithful geyser in Yellowstone.

"There are other moons in the solar system that have liquid water oceans covered by kilometers of icy crust," said Andrew Ingersoll, an atmospheric scientist a co-author of the research published in Science. "What's different here is that pockets of liquid water may be no more than 10 meters below the surface."

In the near-vacuum conditions at the moon's surface, liquid water would boil away into space, erupting forcefully into the void and carrying particles of ice and liquid water along with the vapor. When the scientists analyzed the jets and plumes, they found most of the particles eventually fall back to the surface, giving the south pole its extremely bright veneer. Enceladus is considered the most reflective object in the solar system.

The particles that escape the moon's gravity enter orbit around Saturn, forming the planet's E ring, the scientists said.

The team found the icy geysers because Cassini's images have revealed the geology of Enceladus in startling detail, including relaxed craters and extensive surface cracks and folds. The scientists said the moon probably has undergone geologic activity over its entire 4.5-billion-year history, from its formation to the present, but the southern pole seems to be the only place where liquid water may currently exist near the surface.

Telltale geologic features throughout the southern hemisphere of Enceladus also point to a change in the body's shape with time. Porco's team thinks these features could be related to an episode of intense heating in the moon's past, which might, in turn, explain the anomalous warmth and current activity at the pole.

The sources of this warmth remain a major puzzle, and may involve some combination of tidal flexing and heating of the interior by naturally radioactive material. Radioactivity could provide enough heat to power the geysers, which erupt from the narrow warm fractures called tiger stripes seen crossing the southern pole. Whether such a phenomenon could generate enough energy to produce the amount of heat observed is uncertain.

"Active water geysers on little Enceladus are a major surprise," said Torrence Johnson of NASA's Jet Propulsion Laboratory in Pasadena, Calif., and another research co-author. "We're still puzzled about the details and energy sources, but what's exciting is that Enceladus obviously figured out how to do it. Now it's up to us to crack the mystery."

If the findings stand, they would suggest that other - and possibly many - of Saturn's 46 moons and Jupiter's 63.

"We previously knew of at most three places where active volcanism exists: Jupiter's moon Io, Earth, and possibly Neptune's moon Triton," said John Spencer, another team member, of the Southwest Research Institute in Boulder. "Cassini changed all that, making Enceladus the latest member of this very exclusive club, and one of the most exciting places in the solar system."

Candy Hansen, a Cassini scientist at JPL, said the geysers on Enceladus might also be related to the abundance of oxygen molecules permeating the Saturnian system. "As Cassini approached Saturn ... we had no idea where the oxygen was coming from. Now we know Enceladus is spewing out water molecules, which break down into oxygen and hydrogen."

In the spring of 2008, scientists will get another chance to look at Enceladus when Cassini flies within 350 kilometers (approximately 220 miles) above the moon's surface.

"There's no question, along with the moon Titan, Enceladus should be a very high priority for us," Jonathan Lunine, Cassini interdisciplinary scientist, University of Arizona in Tucson. "Saturn has given us two exciting worlds to explore."

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