Cassini Finds Signs of Liquid Water on Saturn's Moon
A new image of Saturn's moon Enceladus backlit by the Sun show the fountain-like sources of the fine spray of material that towers over the south polar region. The image is greatly enhanced and colorized.
Credit: NASA/JPL/Space Science Institute

This story was updated at 2:52 p.m. EST.

Saturn's moon Enceladus may have pockets of liquid water lurking beneath its surface, feeding great jets that spew from the satellite and hinting at the possibility of a habitable environment, researchers said Thursday.

Observations from the Cassini spacecraft currently studying Saturn and its myriad moons shows Enceladus, one of the brightest objects in the Solar System, to be a geologist's dream, with an active plume spewing water and other material spaceward, as well as a hot spot of thermal activity at its south pole.

"This finding has substantially broadened the range of environments in the solar system that might support living organisms, and it doesn't get any more significant than that," said Carolyn Porco, Cassini imaging team leader at the Space Science Institute in Boulder, Colorado, in an e-mail interview. "I'd say we've just hit the ball right out of the park."

Porco led one of nine studies of Enceladus, all of which are detailed in this week's issue of the journal Science, based on Cassini's observations from three flybys past the moon - each closer than the last - in February, March and July of 2005.

Enceladus' active nature points toward subsurface water reservoirs beneath its icy exterior, much like that believed to churn just under the surface of Jupiter's moon Europa, researchers said. But unlike Europa, which researchers believe harbors a vast ocean beneath kilometers of thick ice, Enceladus' water may be just below the surface.

"What's different here is that pockets of liquid water may no more than tens of meters below the surface," said Andrew Ingersoll, a Cassini imaging team member and atmospheric scientist at the California Institute of Technology, in a statement.

Plume science

Cassini caught hard evidence of Enceladus' plume since last year, though scientists were unsure of what powers the jets of particles blowing into space. The moon is only the third other body in the Solar System - Earth, Jupiter's moon Io and possibly Neptune's moon Triton are the others - known to have active volcanic processes, researchers said.  

Porco's team found evidence that the jets may erupt from buried pockets of water at temperatures above 32 degrees Fahrenheit (0 degrees Celsius) like a frigid geyser.

The close proximity of water, rock and the south pole's thermal hot spot puts Enceladus on the list of possible harbors for biological activity, some researchers said.

"You've got liquid water, and it's liquid water interfacing with rock...and there's energy," NASA Cassini scientist Candice Hansen-Koharcheck told "We've got the very most basic ingredients here, and so that notches it up on the biological potential list."

Cassini's instruments could help pin down Enceladus' liquid water sources in future passes, researchers added.

"If a wet domain exists at the bottom of Enceladus' icy crust, Cassini may help to confirm it," writes Jeffrey Kargel, a research scientist with the University of Arizona's Department of Hydrology and Water Resources, in a related article in Science.

But the spacecraft, Kargel wrote, will not be able to determine whether subsurface water pockets could offer a habitat suitable for living organisms.  

"Any life that existed could not be luxuriant and would have to deal with low temperatures, feeble metabolic energy, and perhaps a severe chemical environment," Kargel wrote. "Nevertheless, we cannot discount the possibility that Enceladus may be life's distant outpost."

Other mysteries

Cassini's Enceladus flybys also answered other questions surrounding the role of the moon's plume in the near-Saturn environment.

The plume, which a team of researchers led by Hansen-Koharcheck at the Jet Propulsion Laboratory in Pasadena, California believe may have been erupting continuously for 15 years, appears to replenish Saturn's E-ring with material and provide the source of oxygen and hydrogen permeating the planet's neighborhood.

"It's definitely the water, there's no doubt about it," Hansen-Koharcheck said, adding that trace amounts of other materials are also present in the plume.

Cassini deputy project scientist Linda Spilker told that the plume activity on Enceladus is much different from the volcanoes on Jupiter's moon Io, where material eventually settles back on the surface once it erupts. Instead, Enceladus spews material directly into space and Saturn's E-ring.

"If you turned Enceladus off, you would probably turn off the E-ring," Spilker added.

The plume's activity appears tied to the thermal hotspot at Enceladus' south pole, the source of that internal heat remains undetermined.

"We think we can rule out a radioactive related source," said John Spencer, a Cassini scientist with the Southwest Research Institute in Boulder, adding that tidal heating from the gravitational pull of nearby Saturn is a more likely culprit.

Cassini's next chance to take a close look at Enceladus will occur in 2008, when the probe will swing within 220 miles (350 kilometers) of the small moon, though the probe may have a few long-distance views before then, researchers said.

"We're all going to have to patiently wait," Hansen-Koharcheck said.