WASHINGTON, April 3 (Xinhua) -- New gravity data from the Cassini spacecraft showed that Enceladus, one of Saturn's smaller moons, harbors a large, possibly regional subsurface ocean with a rocky seafloor.
The study, published Thursday in the U.S. journal Science, indicated that a roughly 10-kilometer-thick layer of liquid water lies beneath 30 to 40 kilometers of crustal ice at the south pole of the 500-kilometer-diameter Enceladus.
Italian and American researchers investigated the moon's gravity field and the notable asymmetry it exhibits between northern and southern hemispheres to reach these conclusions.
"Using geophysical measurements, we have been able to confirm that there is a large ocean beneath the surface of Enceladus' south-polar region," said co-author David Stevenson, professor of planetary science at the California Institute of Technology.
"This provides a possible source for the water that Cassini has seen spewing from the geysers in this region," Stevenson said.
The researchers analyzed the so-called Doppler Effect data from three of Cassini's flybys between 2010 and 2012, which brought the spacecraft within 100 kilometers of Enceladus' surface.
They found that the southern polar region of the moon doesn't have enough mass at its surface to account for the hemisphere's gravity field, suggesting that something dense below the surface of Enceladus, probably liquid water, must be compensating.
"This water ocean ... may extend halfway or more towards the equator in every direction," Stevenson added. "This means that it is as large, or larger, than Lake Superior," the second largest lake on Earth.
In addition, this subsurface ocean on Enceladus sits atop silicate rock instead of ice, which means that the environment there is ripe for complex chemical reactions, including some that, with the help of an energy source, might create conditions like those on the early Earth, the researchers said.
The findings may also help explain the mineral-rich jets of water vapor that were first observed flowing from long, distinctive fractures in the moon's southern polar region, called tiger stripes, in 2005, they said.
The findings made Enceladus eligible to join the ranks of Titan and Europa as a moon that may have liquid water splashing around inside of it.
"Enceladus shows some similarity to Europa, a much larger moon of Jupiter, which, like Enceladus, has an ocean that is in contact with underlying rock," said Stevenson. "In this respect these two bodies are of particular interest for understanding the presence and nature of habitable environments in our solar system."