[X] My Assistant

[Olvegg]

New article in New Scientist

[nprev]

Hmm. Will Cassini ever make a direct overflight of this feature? I don't see how any of these questions can be answered unless and until we get a more-or-less nadir view of it (preferably more than one in order to investigate this possible variability).

Interesting possibilities here, though. How much do we really know about organic chemistry at Titan's surface and subsurface temperatures, to say nothing of phase change dependencies for such substances under various pressures, catalytic interactions, etc., etc.? The possibilities seem endless; even active, complex adiabatic processes do not seem to be beyond the pale.

I think it's wise to remember how exceedingly challenging Titan is to our preconceptions and inherent prejudices. This place is nothing like anywhere else in the System; analogies and assumptions are therefore implicitly suspect. Given this, constructing a working hypothesis for Hotei Arcus if it is in fact a "volcanic" feature will require considerably more data, probably more than Cassini can provide.

[JRehling]

The implications of volcanism on a world where H2O is the dominant mantle material elude me. My thoughts jumble up... is this mess untangled for someone else:

Let's assume that Titan has a rocky core and an H2O mantle. The heat driving volcanism has some radial distribution: If it is tidally-driven, then it would originate at radii somewhat out from the center. That would seem to create a layer of liquid water BELOW the icy mantle, right? Because if liquid water were atop ice, it would want to get down below it. Whereas if it reached the boiling point, it would want to escape upwards.

Water is more malleable than ice or rock, so any water layer would be a locus of tidal deformation and therefore tidal heating. If the heating did happen to have a stable equilibrium with the water liquid but not freezing or boiling, then Titan might be inactive. But if anyplace in that liquid reservoir crossed over to boiling, then some sort of upward vent would be created, along with an increase in reservoir volume. A minor vent would run out of steam (literally) after spending itself into the cooler icy mantle. That suggests an equilibrium where that "vent" is spread out in all directions, just adding some volume to the reservoir at the expense of the mantle. Activity of that sort could take place regularly if there's any input allowing new flareups, but with gravity wanting to spread the plastic ice back into a uniform spheroid swallowing any vents.

If a vent made it all the way to the surface, however, you might get a different stable equilibrium with continual cycling of surface/mantle/reservoir over geological time, with the vent continually pulling boiled H2O up from the reservoir to the surface -- but not if the vent cools to below 100C -- then the water would want to dive back down below the ice. So we might see vents that flatten and mushroom at the radius where they run out of steam (again, literally), but maybe allow cycling of the water downwards.

Another confound to all of this is the change in melting/boiling point at high pressures.

I think it's going to be seriously difficult to model the possible scenarios.