Saturn’s watery moon could harbour life

From New Scientist 10 March 2006

Saturn’s tiny moon, Enceladus is brimming with liquid water and cannot be ruled out as a distant outpost of life. So say Cassini mission scientists after studying the geysers of ice particles and water vapour found spewing out of the moon’s south polar region in 2005. Their analysis all but rules out the possibility that the plumes are caused by water ice sublimating directly into space. Instead the most likely scenario involves significant quantities of liquid water boiling off from near-surface reservoirs.

The conclusion leaves open the tantalising question of what energy source is keeping the water in its liquid state. The decay of radioactive elements in the moon’s rocky core cannot, on its own, generate enough heat to do the job. An insulating shell of clathrate hydrates – a form of water ice containing trapped gas molecules – could help Enceladus retain more heat. Additional warming may come courtesy of the gravitational tug of war between Enceladus and Dione, a neighbouring moon.

A chance to learn more will come during Cassini’s next close pass of Enceladus, scheduled for 2008. Exploring whether or not Enceladus represents a bona fide habitable zone will be a job for a future mission. The likelihood of liquid water “is thrilling beyond imagination”, says Carolyn Porco, head of the imaging team. “If we had done nothing else, these findings alone would have made the Cassini mission worthwhile.”