A Drizzly Cryo-Nevada

Or something like that... see below.

Apply Earth geomorphic analogues at your peril, however. CH4 is not a polar molecule like H2O, and thus liquid methand is not a van der Waals fluid, not (perhaps) as "wet" as water. And the rock being eroded is predominately 90K water ice mixed with organics, presumably.

Whatever it is, you got to love saying "cryoplaya"!

From: Bruce Moomaw
Date: Fri Jan 21, 2005 3:57 am
Subject: Titan as a rainy world

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Those of you who watched that rather intimate little Huygens press conference (virtually all the talking was done by Tomasko, Zarnecki and Tobias Owen, in a rather small room) already know all this. But for those of you who didn’t: the first big discovery of Hugyens seems to be that methane rain, contrary to what a lot of theorists thought, DOES hit the surface of Titan directly—and pretty frequently. The landing site is (as I suspected) rather like a terrestrial desert with arroyos and a big playa, which seem to be currently dry—but they were rained on quite a short time ago (the general impression was left that it was less than a year), and the playa is still muddy. And that smooth, pebble-free region running through the middle of the post-landing photo is indeed thought to be a small, recently wet steream channel (although it’s not wet now; they haven’t seen any signs yet of liquid pools or puddles actually on the playa’s surface at the moment). I imagine the rain comes from those small wandering clumps of methane clouds seen by Cassini; they may be small, but they seem to be very moist, and they may be lower-altitude than previously thought. They may, in fact, be pretty damn dramatic thunderstorms.

Some of the arroyos were definitely carved by surface rainfall; others, with stubbier branches, seem to be sapping channels coming from springs. Also, John Rehling was right in noting that some runoff channels run across the “peninsulas” of stone-studded terrain sticking into the playa. The suggestion was made that these are places where the liquid poured from one part of the playa into a somewhat lower part—but I’d like to know whether the possibility can be completely ruled out that both they and the springs might be tidally driven phenomena instead, if the tides on Titan are as powerful as has been suggested. Anyway, the rain washes the dark smog off higher terrain on Titan and it accumulates as a dry crust in the arroyos and playas after the liquid evaporates, as we thought. I imagine that—given the very slow rate at which the smog is produced—virtually all of it actually gets caught up in the raindrops and carried down onto the surface by them. I suspect that those light-colored streaks seen by Cassini to the leeward side of high features on Titan are not, as I thought, wakes where dry smog dust has not been blown by winds—but rain shadows instead.

The second big revelation, although less was made of this, is that cryovolcanism is definitely occurring on Titan, and pretty vigorously. One photo taken from serveral km up showed, plain as day, a very light-colored narrow “tongue” of very clean water ice stretching across the landscape, with arroyos starting immediately at its edges and flowing away from them—as though it was a fairly high, smooth dome of water ice extruded from underground, with the surface so smooth and hard that the rain falling on it doesn’t erode it, but instead runs off its slopes onto the older ground-up water ice regolith immediately to each side of it and starts carving gullies only then. But that means that the icy surface of this ridge must be relatively recent, and hasn’t been ground up yet into loose ice regolith by meteoroid impacts and whatever other processes slowly grind up the surface ice of Titan. Also, they got some good stereo pairs from the photos—and the ridge running close to and parallel to the shore in that famous photo of the runoff channels near the shoreline, with rainfall channels running off it on both sides, must be about 100 meters high but only several hundred meters wide. In short, Titan is NOT the flat world I had suspected it was—except in the basins where the liquid runoff and muddy sediment have accumulated. (No speculation from them as to what’s driving the cryovolcanism. Tidal heating?)

Zarnecki confirmed that lab tests do indeed show that the penetrometer profile can be simulated by the instrument’s staff ramming through a thin dry surface crust and into softer muddy material below, and that the whole probe seems to have sunk 10-15 cm into the mud. And the heated GCMS inlet, starting 3 minutes after landing, evaporated enough liquid methane out of the mud to raise the gaseous CH4 level going to the GCMS by 30%. (The only other mention made at this point of any other substances detected by the GCMS is that some heavier organics also seem to have been vaporized out of the mud by the heated inlet.) It starts to look as though the methane clouds build up just below the methane cold trap that separates Titan’s troposphere and stratosphere, and as I say may grow into pretty dramatic thunderstorms—although Fulchignoni, who was at the press conference but did very little talking, didn’t say anything about any possible detection of radio bursts from distant lightning bolts.

Other things I would have liked to hear more about but which weren’t mentioned, besides tides and lightning: the argon level; the altitude (once again) of the lowest pre-landing photos (although the photos they did get, having been greatly improved by further processing, seem more than adequate to give us a good idea of what’s going on on Titan); those possible clear liquid droplets on the DISR’s windows; and the significance, if any of that double spike in the echo sounder’s data (a dried surface crust with a moderately deep mud layer below it, as hinted by the penetrometer?) But Titan has turned out to be a nice dramatic place after all, and much wetter than I really expected it to be—now unquestionably the first world besides Earth to have a good deal of liquid on its surface (and not just ethane, but liquid methane) -- as well as being a lot more internally active than anyone seems to have suspected. In short, Huygens—even with only one communications channel working—has delivered the goods, in no uncertain terms