Although very properly linked via 'Conferences and Publications' this is an exclusively Titan topic so it seems right to locate any discussion of the papers here.

For convenience, the link again: http://www.unmannedspaceflight.com/index.p...ic=5857&hl=

I was struck by this sentence from the concluding section of the second paper (Tobie et. al.):

"Even though the interior is mostly composed of water ice and various hydrates, the near-surface is probably dominated by organic materials. Interaction of liquid methane and other liquid hydrocarbons with such solid organic deposits probably shaped the landscape of Titan. Water ice and hydrated materials should dominate only in cryovolcanically active provinces."

I would add that to resupply the atmospheric methane the 'cryovolcanism' need not even be sufficiently violent to bring water ice all the way to the surface. On this assessment whatever forms the bright highlands of Titan is not water ice.

'struck' ? Sorry, but this has been obvious for a long time. To quote myself from 2 days after the first
Cassini encounter TA (Oct 2004)

"With the radar in its active mode, it is like shouting at Titan and listening for the echoes," said Dr. Ralph Lorenz, Cassini radar team member, University of Arizona, Tucson. "But we can also just listen with the sensitive radar receiver, the radiometry. The radiometry data shows early indications of the composition of the surface materials. One interpretation of what it is telling us is that Titan is a place covered with organics."

http://saturn.jpl.nasa.gov/news/newsreleas...elease20041029/

The deep bedrock is water ice (and/or ammonia hydrate and/or clathrates) but certainly the upper veneer
seems to be organic-rich more or less globally. There is also the question of how to form the 'karst' lakes
in the north - water ice shouldnt be that soluble in liquid hydrocarbons, but other organics might be..

Yeah, I'm familiar with the veneer idea and I did know we're not looking at naked bedrock ice. Maybe I mistook the word veneer - I took it to mean a few mm of 'smust' or whatever, possibly removable by a rainstorm. Now I'm wondering if the ridges and river-dissected islands (like the ones Huygens observed) could be built almost entirely of organic materials, with the presumed icy substrate actually a long way further down - maybe a kilometer or more. In another thread there was mention of a possible future Titan lander designed to study ices. I assumed (again perhaps erroneously) that this meant aqueous ices. I will try to locate that. Always glad to have my muddled assumptions straightened out.

On the northern 'karst' lakes - if they are formed into kilometer-deep piles of organic sediment rather than water ice 'rock' then presumably you wouldn't need to dissolve water ice to form them.

Mike, you might like to try a beaker of powdered plastic (sawdust? coffee?) and see how well that holds on to the heptane.

Right. Even long before Voyager and the idea of the methane/ethane ocean, Don Hunten presciently
suggested that Titan should have a kilometer or so of 'photochemical debris' on its surface....

As for heptane retention, wouldnt hurt to explore other analogs, but I suspect it will be the physical
properties (particle, and thus pore, size) that will control the heptane loss, rather than the chemical
composition of the grains.

That was another big surprise in the whole heptane/silica experiment. I had assumed that the non-polar heptane would have beaded up or not interacted very well with the polar silica surface (like water on a nasturtium leaf). Instead, the heptane did a fantastic job of wetting all the silica grains. I've got some interesting images of the changes fo the silica surface as it dried that I'll post shortly.

It seems that the non-polar low-surface tension hydrocarbon solvent is more than happy to crawl all over and wet a polar surface. So the smaller grains should have the maximum efficiency at transferring material from the lower depths to the surface (but still with a factor that should depend on depth.)

However, I'm not sure that the inversed experiment would work the same way: using a polar solvent (water) with non-polar substrate (carbowax beads). I think the surface tension of the water would inhibit full wetting (thus maximal surface for evaporation) of the grains.
[BTW, this is a major problem for spraying pesticides onto plants. The organic materials don't like to go into water, so various formulations are created to help them dissolve/diffuse evenly into the water. Many formulations and products carry the term "WP" which stands for "wettable powder".]

As for the 'karst' lakes, the lake solvents don't need to fully dissolve the substrate, the solvents just needs to break it down or weaken the structure.

If there were organic-coated water ice grains all stuck together, then you dissolve the organic coating in hydrocarbon solvent, the remaining insoluble water ice grains are all in a suspension and can settle out or be physically carried away.

[BTW, this is very similar to how "Wettable powders" work for pesticide formulations, there is an outer aqueous soluble coating of the insoluble pesticide grain. Dissolve the coating, et voila! the grain is in aqueous suspension.]

I'm a big fan of hydrocarbon or organic-coated water ice grains on the surface Titan.
It could explain the spectral signature (kinda-sorta water-ice like in some spectral regions)
and also the dielectric constant (way too low for ice)
and also the visual characteristics: bright "purer" highlands, rewoked in the channels, and even more processed and reworked in the basins.

-Mike