Scientists, using a computer model, have unravelled the mystery behind the sustained eruptions on Saturn's icy moon Enceladus, which serves as a leading candidate for extraterrestrial life.
The Cassini spacecraft has observed geysers erupting on 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 do not tend to continue for long. When you do see eruptions that continue for a long time, they'll be localised into a few pipelike eruptions with wide spacing between them," said Edwin Kite from University of Chicago.
But Enceladus, which probably has an ocean underlying its icy surface, has somehow managed to sprout multiple fissures along its south pole, researchers said.
These "tiger stripes" have been erupting vapour and tiny frost particles continuously along their entire length for decades and probably much longer, they said.
"It's a puzzle to explain why the fissure system doesn't clog up with its own frost," Kite said.
"And it is a puzzle to explain why the energy removed from the water table by evaporative cooling doesn't just ice things over," he added.
According to him, what is 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.
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's surface, and so I hope that this model will be useful for Europa as well," said Kite.
Kite and Allan Rubin from Princeton University wanted to know why Enceladus maintains a base level of cryovolcanic activity, even when at that point in its orbit where the fissures should clamp shut and curtail the eruptions.
The findings were published in the journal PNAS.
