Remember those geysers on Enceladus we’ve been gushing about? Scientist Susan Kieffer proposes a sub-freezing theory for the plumes of ice and gas bursting from its south pole. Geologists among us might remember what a clathrate is. The University of Illinois scientist tells us:
Nitrogen and methane are nearly insoluble in liquid water, but highly soluble in frozen water – in an ice phase called clathrate. When clathrate is exposed to a vacuum, the gas molecules burst out, ripping the ice lattice to shreds and carrying the fragments away.
Kieffer and colleagues have proposed an alternate model to explain the plume on Enceladus. The gases in the plume, they propose, are dissolved in a reservoir of clathrate under the water ice cap in the south polar region. The clathrate model allows an environment that would be 80 to 100 degrees Celsius colder than liquid water, with a “Frigid Faithful” plume emanating from clathrates, rather than from liquid water reservoirs.
“Exposed to near-vacuum conditions by fractures at the south pole, the clathrates decompose violently, spewing out nitrogen, methane and carbon dioxide gases, and ice particles; as well as leaving fracture walls coated with water ice,” said Kieffer, who is also a professor in the university’s Center for Advanced Study, one of the highest forms of campus recognition. “Some ice particles and ice coatings evaporate to produce the water vapor observed with the other gases,” she said.
If you don’t have a subscription to the journal Science, you can get a brief story on this at SpaceRef.
Here’s a Cassini temperature scan from last year. Temps not in Fahrenheit, but Kelvin. Perspective: 292K is room termperature.
Kieffer’s clathrate theory would require temperatures of 170-190K, not the 90K indicated over that sulcus (groove). I’m assuming the Cassini probe was measuring an average temperature over the whole orange box there. If so, the warm box is about 20% groove and that whole groove would average about 150K. Are both the sides and floors of the groove covered with clathrate? Or is there a pond just under the surface?
When Cassini flies 15 miles over the Enceladus south pole in 2008, it should get a much closer look at the sulci. If it finds specific temperature readings on the floor and/or walls of those sulci, the matter might be resolved. But as is true in many scientific things, it’s possible than not just clathrates or the liquid water are present and working, but both.