Wheaton professor's research points to a sea of water beneath ice on Saturn's moon Enceladus

Images from the Cassini space probe a year ago revealing huge geysers spewing from the southern polar region of one of Saturn's moons generated excitement in the world of planetary science. The news of geysers on Enceladus--which were observed clearly silhouetted against the blackness of space--has fueled new research to determine whether they are fed by liquid water under the south pole, and whether there are conditions favorable for life beneath the ice.

A new study by Associate Professor of Geology Geoffrey Collins and another Massachusetts scientist suggests that there is a sea of liquid water trapped beneath the ice on Enceladus. The paper, ''Enceladus' south polar sea,'' by Collins and Jason Goodman of the Woods Hole Oceanographic Institution will soon be published in Icarus, the International Journal of Solar System Studies. Collins was also interviewed on the subject for the online program Planetary Radio.

''Our research is an attempt to tie together several different lines of evidence that emerged after the discovery of the active south pole into one explanation,'' says Collins, a planetary geologist and lead author of the new paper. ''Specifically, we focused on the shape of Enceladus--a piece of evidence that not many other researchers have been looking at. The shape of Enceladus is not quite what you would expect; it seems as if the south pole has been punched in.'' To fit the shape, Collins and Goodman envision a huge pit, two to three kilometers deep, centered on the south pole and covering a large portion of the southern hemisphere.

The location of this large pit is also where Enceladus is currently radiating huge amounts of heat. Collins and Goodman theorized that these two clues add up to a large pool of ice-melt beneath Enceladus' south pole. They developed a computer model of the interior of Enceladus with ice layered on top of rock, and then heated the base of the ice layer under the south pole. They found that their model could, in fact, produce a stable south polar ''sea,'' trapped like a bubble between the rock below and several kilometers of ice above, and surrounded on all sides by walls of unmelted ice.

How does a south polar sea explain the observed shape of Enceladus? Since liquid water is more dense than solid ice, the surface will contract when it melts. By assuming a reasonable density for the rocky core, and turning on a heat source equal to the amount of heat observed to be radiating from the south polar area, Collins and Goodman found that the size of the pit was just right to explain the shape of Enceladus. ''That's when I thought we might be on to something,'' says Collins. What's more, the formation of the large pit could cause the rotational axis of Enceldus to shift, placing the pit squarely on the pole.

The researchers suggest important sets of data that could test their south polar sea hypothesis. First, determining the gravity field of Enceladus would prove or disprove the prediction that Enceladus is internally differentiated. Second, measurement of the pull of gravity over the south pole could help to detect density anomalies below the surface, such as a large bubble of liquid water. Finally, determining its detailed shape could map out the topographic highs and lows predicted by the physics of the model. Cassini has already performed three of four close flybys of Enceladus planned for the primary mission, but there are seven more flybys planned for the two-year extended mission.

''We're very interested in what these flybys and additional data will reveal,'' says Collins.

What about the connection between liquid water and life?

''Just about anywhere on Earth where you find liquid water, you find life,'' Collins points out, ''even in extreme environments. There may be liquid water on Enceladus, but the question is, is there anything to eat?''

Collins' research explores geological processes on the icy satellites of the outer solar system. He has been involved with various NASA projects such as the Galileo mission to Jupiter and the Cassini mission to Saturn.