Eruptions on icy moon of Saturn explained
The Cassini spacecraft has observed geysers erupting on Saturn’s moon Enceladus since 2005, but the process that drives and sustains these eruptions has remained a mystery. Now, scientists at the University of Chicago and Princeton University have pinpointed a mechanism by which cyclical tidal stresses exerted by Saturn can drive Enceladus’ long-lived eruptions.
“On Earth, eruptions don’t tend to continue for long,” said Edwin Kite from the University of Chicago. “When you do see eruptions that continue for a long time, they’ll be localized into a few pipe-like eruptions with wide spacing between them.”
But Enceladus, which probably has an ocean underlying its icy surface, has somehow managed to sprout multiple fissures along its south pole. These “tiger stripes” have been erupting vapor and tiny frost particles continuously along their entire length for decades and probably much longer.
“It’s a puzzle to explain why the fissure system doesn’t clog up with its own frost,” Kite said. “And it’s a puzzle to explain why the energy removed from the water table by evaporative cooling doesn’t just ice things over.”
What’s needed is an energy source to balance the evaporative cooling. “We think the energy source is a new mechanism of tidal dissipation that had not been previously considered,” Kite said.
“I was very happy to see this new work by Kite and Allan Rubin from Princeton University, New Jersey, that brings to the fore a process that had escaped notice: the pumping of water in and out of the deep fractures of the south polar ice shell by tidal action,” said Carolyn Porco, head of Cassini’s imaging science team and a leading scientist in the study of Enceladus.
Astrobiology experiment
Enceladus, which Kite calls “an opportunity for the best astrobiology experiment in the solar system,” serves as a leading candidate for extraterrestrial life. Cassini data have strongly indicated that the cryovolcanic plumes of Enceladus probably originate in a biomolecule-friendly oceanic environment.
Cryovolcanism may also have shaped the surface of Europa, one of Jupiter’s moons. “Europa’s surface has many similarities to Enceladus’ surface, and so I hope that this model will be useful for Europa as well,” Kite said.
One of the problems that attracted Kite and Rubin was the anomalous tidal response of the Enceladus eruptions. The eruptions reach their peak approximately five hours later than expected, even when taking into account the 40 minutes needed for the erupted particles to reach the altitude at which Cassini can detect them. Other scientists had previously suggested reasons for the lag, which included a delay in the eruptions as well as a squishy, slowly responding ice shell.
“The new proposal is really a way to get a delay in the eruptions. You really don’t need to propose any terribly squishy ice shell to do it,” Porco said.
source; http://www.astronomy.com/news/2016/03/computer-model-explains-sustained-eruptions-on-icy-moon-of-saturn
