[X] My Assistant

[Mongo]

A Retraction

As I was continuing to re-read Lifting Titan's Veil, I came agross this paragraph on page 153:

Although methane is a good analogue for water on Earth, methane glaciers look unlikely because methane doesn't seem to be solid at Titan's surface temperatures. Although the freezing point of pure methane is about 90K, roughly the same as the surface temperature of Titan's high latitudes, the antifreeze effect of nitrogen lowers the freezing point below 80K, lower than the temperatures we believe occur anywhere on Titan -- even at the summits of its highest mountains.

Oh well. A nice theory, ruined by an inconvenient fact. But this still leaves the question of why the polar lakes appear to be mostly confined to a few sub-regions within the greater north and south polar regions. Without more detailed imagery than the Cassini SAR can provide, there is no way of knowing if the non-lake areas are part of the drainage basins of the lake areas. If they are, then presumably the local precipitation drains to one of the lakes. If they are not, then perhaps the ground is geneally permeable, and the methane and ethane simply sink down to the local methane table, which in those areas lies below the surface. If all the lakes are at about the same altitude, the lakes/seas would presumably be those places where the methane table is above ground level.

Bill

[ngunn]

See post 55 this thread.

[tty]

the lakes/seas would presumably be those places where the methane table is above ground level.

That, as a matter of fact, is an excellent definition of a lake/sea!

[Mongo]

That, as a matter of fact, is an excellent definition of a lake/sea!

Okay, I should rephrase and expand that sentence into: the only places where the methane table is above ground level are located in the areas where we see lakes/seas -- so those areas may be topographically lower than the rest of the polar regions, and the rest of the region may be permeable to methane..

Bill

[Juramike]

I agree with Mongo.

If this is correct: The altitude of the lake levels of the polar lakes should all be about the same in the same methanological unit. If you put dye in one lake, it should percolate throughout the area and color several (all?) lakes. This would be a pretty good test of the karst hypothesis.

So... assuming that the equatorial basins may also be contained in one of the units, why aren't they also filled with liquid?

Are the equatorial basins at a higher (too high) a level than the methanofer (i.e. filled in with sand, so the methane is way down deep)
Or is there something special about the polar regions that seals in this area?
Or is there something special about the washed in gravel in the equatorial region that helps absorb the methane into the xtal lattice?

According to VIMS data, the south polar region seems to be a different terrain type. I'll assume the north polar region is similar.

Has anyone seen any altitude data comparing equatorial zones (Shangri-La basin) with any of the polar lakes. Or even of the polar lakes with each other?

-Mike

[ngunn]

This could be on the right lines but I think some rather sweeping assumptions have crept in. First, why assume that all the icy 'bedrock' materials of Titan behave similarly? There could be as much variety as there is amongst terrestrial silicate rocks, with a complete spectrum from permeable to impermeable, resulting in a methane table that is far from regionally flat. Then there is the possibility that over time some of the lakes 'paint' their basins with a sealing layer that inhibits drainage. That could depend in complex ways on the local geology, the size of the catchment area, the mix of organics washed in, the age of each lake basin, and so on. Some lakes have drainage both in and out, others only in. On Earth this results in fresh or salt water. What are the implications on Titan?

In short, I think there are far too many unknown parameters at this stage for any kind of synthesis to emerge, as the 'Karst or Cryovolcanos' paper demonstrates. I think we're still at the stage of data-gathering and trying to imagine every possible scenario so that no possibilities are overlooked. Of course people like to find 'answers', preferably within the lifetime of their research grant. (And of course here we like them daily or weekly!) However there is no guarantee that Titan will oblige, and there is nothing more obstructive than a premature consensus.

[ngunn]

Some more possible complications:

Time-variant clogging and unclogging of methanifers (or should we say alkanifers?) on a variety of time and distance scales.

Isostatic effects - are the lakebeds slowly sinking under their own weight as sediment accumulates, creating localised 'geosynclines' or the inverted equivalent of diapirs within the crust? Would this process sometimes create raised rims? Would it tend to lead to 'bunching' of lakes?

Could the polar terrains be dotted (perhaps in three dimensions) with many generations of 'fossil' lake residues? What forms might these take and how might they relate to the present lake distribution and drainage pattern?

[belleraphon1]

Karst, Calderas, or Craters.....

All...

I have to agree with ngunn in the last post regarding premature consensus.

All our speculations are indeed premature as yet. This world has offered up an icy/organic array of geologic and geochemical processes that, at least visually, seem just as diverse as the Earth's silicate/water cycles.

I am inclined toward karst terrain (except the raised rims on some of these structures are hard to reconcile with that), simply because I cannot imagine all this organic gunk (goo-sphere) drifting to the surface over geologic ages, metamophosing under pressure with occassional episodes of ammonia/water/methanol slurries cooking and brewing away on these materials, and not getting some pretty wierd mechanical properties out of this stuff.

For cryovolcanics, if that is the case, than somehow the most active regions are concentrated here. Perhaps we have a one plume planet? Look at the Tharsis bulge on Mars..... it will be great to eventually get the geoid of Titan.

As for impact craters.... I do not really see a lot of cases of central peak islands.... and if they are old impact craters, the shapes have been grossly distorted over time.

Let's continue to speculate under the knowledge that Titan will eventually (over the next 100 years or so) tell us what we need to know.

But remember.... "we aren't in Kansas anymore, Toto".

WHAT FUN AND HOW GLORIOUS...I am in geek-sphere over the goo-sphere.

Craig

[Juramike]

"There's nothing like data to mess up a good hypothesis".

At this point, there is an ever-expanding list of possibilities and speculation about what could be going on at Titan. Hopefully, the speculation will help foster for future missions and experiments to help explore this mysterious world.

I'll guess that Titan geology may turn out to be even more complex than Earth geology. We may discover new processes that have no terrestrial analog.

This discussion topic has come up with several theories and explanations for the formation of polar lakes. These are premature and based on initial data and most-likely immature assumptions. But that's how science and assumptions gets tested.

What types of observations and measurements would be helpful to help support/refine/propose our ideas?

Is there a way we could use the data we already have at our disposal (e.g. SAR image analysis)?
Are there currently planned observations that will be key to our understanding?

This is a really exciting time as we watch the story unfold.

Whoo-hoo!

-Mike

[ustrax]

This may be useful.
If someone hasn't already made reference to...

[hendric]

Karst, For cryovolcanics, if that is the case, than somehow the most active regions are concentrated here. Perhaps we have a one plume planet? Look at the Tharsis bulge on Mars..... it will be great to eventually get the geoid of Titan.

Well, there is a hypothesis that the reason the Tiger Stripes on Enceladus are at the pole is that the density change caused by the heat source forced the moon to precess. I don't know if that same effect would occur with Titan.

[ngunn]

These lake basins appear at both poles - I'm nearly sure of that - so a single hot plume hypothesis won't do. If any form of cryovolcanism is involved then there must be some way in which the rainfall 'causes' the cryovolcanic activity to appear just near the poles. We have a precedent: on Earth, seawater is implicated in lubricating subduction and helping to drive plate movement. There could be analogous, but very different in detail, coupling on Titan.

[rlorenz]

Nice of you to point that out....

Knowing (as we do now, 2 years on) how much darker the lakes are at N polar
regions, I'd have to guess these particular features in TA (50-ish north)
are more likely to be dried-up lakebed-type features than presently-filled lakes
as seen at higher latitude...

This may be useful.
If someone hasn't already made reference to...

[elakdawalla]

Welcome to UMSF, rlorenz

--Emily

[Mongo]

I second that! Welcome to UMSF.

You need to be warned, though, that a lot of people will be wanting to pick your brains, since we are so interested in Titan (among other things) and you are an obvious 'go-to' guy on that topic.

Bill

post scriptum: I had bought Lifting Titan's Veil as soon as it came out, and loved it -- I had been fascinated by Titan since before the Voyager flybys. I don't suppose that a follow-up or revised edition is planned for anytime soon? I would imagine that it would make more sense to wait until the conclusion of the Cassini Extended Mission before starting such a project.