[X] My Assistant

[Palomar]

Best evidence yet

*...for a shoreline on Titan; they're calling it "dramatic." Area measures 1,060 by 106 miles. Is from Cassini radar, obtained during the latest flyby. Speculation continues regarding seepage of liquid from the ground/ground springs and/or rainfall.

[Guest_BruceMoomaw_*]

The solution to the apparent contradiction seems to be that -- in most locations on Titan where one would see seas or lakes on Earth -- we're looking instead at mudflats, like the one Huygens landed in. Rain is unquestionably MUCH rarer on Titan than on Earth -- and, on top of that, it seems to have very active cryovolcanic processes (driven by tidal heating from Jupiter, according to one startling theory) which are likely to keep pulling near-surface liquid methane and ethane further down into the subsurface and recycling it through Titan's upper crust. So we see very smooth mudflats (composed of both finely ground water ice and accumulated solid organic-smog sediment) -- but not much actual surface liquid.

Jonathan Lunine, in fact, predicted exactly this a decade ago: he said that the only model that could fit all the already-observed facts about Titan was that most of its liquid methane and ethane was in a subsurface aquifer in a highly porous surface layer, rather than in actual liquid bodies sitting directly on the surface. Bingo.

[JRehling]

The solution to the apparent contradiction seems to be that -- in most locations on Titan where one would see seas or lakes on Earth -- we're looking instead at mudflats, like the one Huygens landed in.  Rain is unquestionably MUCH rarer on Titan than on Earth -- and, on top of that, it seems to have very active cryovolcanic processes (driven by tidal heating from Jupiter, according to one startling theory) which are likely to keep pulling near-surface liquid methane and ethane further down into the subsurface and recycling it through Titan's upper crust.  So we see very smooth mudflats (composed of both finely ground water ice and accumulated solid organic-smog sediment) -- but not much actual surface liquid.

The thing is, sure rain is rare, but it still has to happen sometime, and has to be flowing through those channels sometime and gathering sometime into standing liquid. Is Mezzoramia, now, such a place and time? One good reason to think so is that channels seem to link the immediate vicinity of the south pole and Mezzoramia, and the south pole is where the plurality of Titan's methane clouds appear during this season.

Look how big Mezzoramia is. If it is filled by rains originating at 80S and thereabouts, then it is getting a lot of liquid sometime to fill it from brim to brim, and probably not drying up completely very quickly.

Now the hunt for radar-specular glints (or sunshine-specular glints) over the southern dark areas has got to be a priority. Unfortunately, we're racing seasonal changes. By the time extended-mission opportunities to probe these areas come around, it might be too late. We may end up waiting for northern summer and the beginning of standing liquid there, before Cassini's instruments can put the final dot on the i with the issue of standing liquid.

[imran]

The thing is, sure rain is rare, but it still has to happen sometime, and has to be flowing through those channels sometime and gathering sometime into standing liquid. Is Mezzoramia, now, such a place and time? One good reason to think so is that channels seem to link the immediate vicinity of the south pole and Mezzoramia, and the south pole is where the plurality of Titan's methane clouds appear during this season.

Look how big Mezzoramia is. If it is filled by rains originating at 80S and thereabouts, then it is getting a lot of liquid sometime to fill it from brim to brim, and probably not drying up completely very quickly.

Now the hunt for radar-specular glints (or sunshine-specular glints) over the southern dark areas has got to be a priority. Unfortunately, we're racing seasonal changes. By the time extended-mission opportunities to probe these areas come around, it might be too late. We may end up waiting for northern summer and the beginning of standing liquid there, before Cassini's instruments can put the final dot on the i with the issue of standing liquid.

I agree with your assessment. As rare as rain may be, it is still causing widespread channels (some pretty deep and extensive) and draining all of this in what appears to be seas. Some channels we are seeing require long standing presence of liquid. Cryovolcanic processes alone cannot account for what we are seeing. Titan's surface has been significantly altered by the action of surface liquid. A major effort of Cassini's extended mission should be focused in trying to solve this mystery and the south pole area seems to be a good candidate for this.

[Guest_Richard Trigaux_*]

A strong argument in favour of rare but heavy rainfalls is the size of the drainage channels. Usually, on Earth, in regions with a moderate climate, there is much rain but spread all around the year: drainage channels (rivers) flow all the time but are narrow (and they would be invisible on Cassini and Huygens images). But in desert regions, there is much less rain but very violent when it happens, the riverbeds are much larger, we even see flows which are several kilometres wide without a definite river bed. This is very visible in aerial or satellite views of regions like Sahara, which has similarities with Titan landscape:
-Large flow marks forming valleys in mountainous places, and large series of sediment fans in plains.
-in bottom places, temporary lakes form rounded patterns outlined with vegetation (on Earth) and filled with darker dried mud or white salt.
I can just compare what can be seen when flying over Sahara and what is seen by Huygens and Cassini.

[DFinfrock]

[COLOR=blue]As Bruce MoomMaw wrote in Post #10:

"The picture which is now forming pretty clearly of Titan IS one where rains are rare, but (when they do occur) very violent, allowing the carving of such broad arroyos. The reason is that -- paradoxically -- Titan's air is much clearer of aerosols than Earth's is. The only reason that its quite rarified mist of organic aerosols is opaque to visible light from above is simply that the combination of high air density and very low gravity on Titan causes its atmosphere, and the aerosol layer suspended in it, to tower up to an astonishing height. Earth's much thinner air layer is far more densely populated with tiny solid dust particles -- both windblown dust, and salt crystals swept by the wind out of ocean foam -- and so there are far more nuclei in it for water vapor to condense around and form liquid cloud droplets. But in the case of Titan, with its relative lack of nuclei for cloud droplets, local concentrations of methane vapor can rise to far higher levels before liquid methane droplets start to form at all in significant numbers. Once they DO form, however, the high concentration of methane vapor around them causes them to very rapidly grow to large size, and thus fall out as violent local rain -- and flash floods."

This suggests a simple experiment... well, simple by planetary exploration standards. Why not send a cannister into Titan's atmosphere, which, when it burns up on re-entry, releases a cloud of silver iodide or some other rich source of condensation nuclei. If the current model is correct, this release of nuclei should trigger a heavy methane rain. A follow-up probe, similar to the Huygens, could then descend to monitor the rainfall, and examine the expected flash flooding, erosional effects, and standing pools of liquid on the surface.