QUOTE (tasp @ Oct 15 2007, 09:25 PM)
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Is it too early to ponder how these Titanian fluids 'work' the surface ??
We see incised flow features in many locations. Does the fluid flow directly erode into the surface, or do entrained minerals or grains aid the 'cutting' process ?
On earth water is a polar solvent, IIRC, most of the candidate fluids for Titan are non-polar, do those fluids 'do' erosion the same way ?
A hydrocarbon solvent should behave sorta-kinda similar to water erosion on Earth:
1) Any "chunks" or pieces of material carried along the stream and bouncing along as sediment grains will physically abrade the streambed. The chunks could be loose pieces of ice sand, insoluble salts, or insoluble organics. (Just like the muds, sands, boulders and rocks in a meltwater stream during flood stage).
2) Hydrocarbon solvent may leach out (dissolve) emplaced organics on the surface. (The organics having been emplaced during geological processes forming the surface. For example: water circulating around through pores after an impact or cryovolcanic event could emplace veins of partially soluble organics. Just like an ore vein on Earth). In this case the ground liquid could chemically dissolve the veins and cut into surrounding hard ice-rock.
3) [I'm speculating here] Additionally, methane may transition to vapor at Titan's surface temperature. So an initial rainfall hitting hot rock, or a flash flood cruising down a gully, could cause an initial methane boil-off. The boiling would start at small cracks and surface defects of the streambed. I imagine that the expansion of the methane bubbles during boiling would physically help expand the cracks and defects to break down the streambed. (Just like freeze-crack-thaw on Earth - except we are dealing with a surface close to the boiling point of the cycling liquid, rather than the freezing point. And since methane contracts when it freezes, it would lack the molecular "oomph" of water's freeze expansion. It is thus at methane's boiling point where things get interesting.)
The important thing to remember is that water ice is pretty much insoluble in pure hydrocarbon solvent. (Additives could help however). Just like how most rock is pretty much insoluble in pure water.
A lot of details can be found in Lorenz and Lunine Icarus 122 79-91 (1996) "Erosion on Titan" .
-Mike