May 30, 2013
Saturn’s Moon Dione May Have A Subsurface Ocean
Brett Smith for redOrbit.com - Your Universe Online
Once considered to be an afterthought when it came to Saturn´s moons, scientists now believe Dione likely had an active geological history after analyzing data sent back from NASA´s Cassini spacecraft.
Cassini´s images suggest that Dione could join Saturn's other moons that are believed to have subsurface activity, Enceladus and Titan. Along with the Jupiter moon Europa, these Saturn moons have some of the highest geological activity in the solar system and are intriguing targets for scientists searching for the building blocks of life outside of Earth. Finding evidence of a subsurface ocean on Dione would be a massive reputation upgrade for the icy sphere.
Cassini, which has been covering the Saturn system for NASA since 2004, detected a faint particle stream coming from the moon using its on-board magnetometer. The craft´s images showed evidence of liquid or slush under its hard icy crust. They also showed ancient, inactive fractures similar to those seen at Enceladus that are known to spray watery ice and organic particles.
According to a report on the findings published in the journal Icarus, some of the most compelling evidence on Dione was surrounding a mountain called Janiculum Dorsa, which ranges from about 0.6 to 1.2 miles high. Under this mountain, scientists found evidence of puckering as much as 0.3 miles long.
"The bending of the crust under Janiculum Dorsa suggests the icy crust was warm, and the best way to get that heat is if Dione had a subsurface ocean when the ridge formed," said study co-author Noah Hammond, a graduate student at Brown University.
According to the scientists, the icy moon is stretched and squeezed as it gets closer to and farther from Saturn in its orbit, causing friction-generated heat. With an icy crust that can slide around Dione´s surface, the gravitational effects of Saturn become exaggerated, multiplying the heat generated by about ten times, Hammond explained. He added that a localized hotspot or a wild orbit could also cause the puckering and particle stream, but that these explanations seemed less likely.
The NASA team said they are currently trying to determine why Enceladus is so active and Dione sits relatively dormant. They theorize that stronger tidal forces or a larger radioactive rock core on Enceladus could have provided more heating.
Despite the differences between the moons, evidence from Dione suggests that liquid subsurface oceans are relatively common on Saturn´s icy satellites. These moons are likely targets for future exploration, along with dwarf planets Ceres and Pluto, which scientists speculate could have oceans beneath their crusts. Ceres is the largest non-planetary object in the inner solar system, while Pluto sits on the edge of the solar system in a region filled with other small planetoids called the Kuiper Belt. Both of NASA's Dawn and New Horizons spacecrafts are scheduled to reach those dwarf planets in 2015.