[X] My Assistant

[volcanopele]

Well, for those who really like RADAR SAR swaths, today is a good day for you. The T13 RADAR swath from April, THE ENTIRE SWATH, has been publically released on the Photojournal.

Titan (T13) Viewed by Cassini's Radar - April 30, 2006
http://photojournal.jpl.nasa.gov/catalog/PIA08552

PIA08604: Xanadu's Meandering Rivers
http://photojournal.jpl.nasa.gov/catalog/PIA08604

PIA08605: Titan's Geological Goldmine - Radar Movie
http://photojournal.jpl.nasa.gov/catalog/PIA08605

[Guest_AlexBlackwell_*]

Perron et al. have a paper in press with JGR-Planets entitled "Valley formation and methane precipitation rates on Titan" (407 Kb PDF preprint). They don't seem to think the Huygens DISR imagery shows any caverns, etc. Here's the relevant passage:

"In terrestrial environments where dissolution causes significant erosion, there is often morphologic evidence of subsurface erosion. Karst terrain, in which surface runoff and groundwater have eroded carbonate bedrock, contains caverns, closed depressions, and discontinuous surface streams [Summerfield, 1991]. Although the images obtained during the Huygens descent are probably a very limited sample of the erosion features on Titan’s surface, it is notable that there are no obvious karst-like features in the dendritic networks near the Huygens landing site."

[tty]

"Although the images obtained during the Huygens descent are probably a very limited sample of the erosion features on Titan’s surface, it is notable that there are no obvious karst-like features in the dendritic networks near the Huygens landing site."

That is not a strong argument. Try using Google Earth randomly and see how long it takes before you hit a spot with recognizable karst features in the river network.
As a matter of fact many of the largest karst areas (e. g. Yucatan peninsula, Nullarbor plain) has no dendritic pattern since all water movement is underground. All you see is the occasional dolin or cenote.

There might well be other karstification mechanisms on Titan than methane dissolving ice. Even here on Earth there are at least three kinds, ordinary karst where water and CO2 dissolves limestone, thermokarst where water dissolves ice and halokarst where water dissolves salt. The latter two are rare though.

tty