Scientists decode eruptions on icy moon of Saturn

New York: Unlocking the mystery behind eruptions on the icy moon of Saturn, scientists from the University of Chicago and Princeton University have revealed a mechanism by which cyclical tidal stresses exerted by Saturn drive Enceladus's long-lived eruptions.

The moon Enceladus -- 500 km in diameter and 1.272 billion km away from the Earth -- serves as a leading candidate for extra-terrestrial life. 

The data from NASA's Cassini probe has strongly indicated that the cryovolcanic plumes of Enceladus probably originate in a biomolecule-friendly oceanic environment.

“On Earth, eruptions don't 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, assistant professor of geophysical sciences at UChicago.

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 vapour and tiny frost particles continuously along their entire length for decades and probably much longer.

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 added in a paper appeared in the journal the Proceedings of the National Academy of Sciences.

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," Kite noted.

The Kite-Rubin model of the Enceladus plumbing system consists of a series of nearly parallel, vertical slots that reach from the surface down to the water below. 

They applied Saturn's tidal stresses to their model on a desktop computer and watched what happened.

Tidal pumping heats the water and the ice shell via turbulence. 

Kite and Rubin have proposed that new Cassini data can test this idea by revealing whether or not the ice shell in the south polar region is warm.

If the new mechanism is a major contributor to the heat coming from the fractures, then the south polar ice in between the fractures may in fact be cold. 

The jury is still on out on this until the results from the final Enceladus flybys of last year are fully analysed.

“The new work 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,” explained Carolyn Porco, head of Cassini's imaging science team.