Titan's changing lakes Options

[Juramike]

I really, really, like the idea of the longer term cycles. I think there's pretty good evidence of base level changes in both north polar regions (currently flooded) and in the south polar regions (currently drier).

A long term cycle will allow polar lakes to dry out as the solvent level drops, while the occasional seasonal rains will incise channels in the dry lakebeds.

-Mike

[ngunn]

I've been checking authors' websites, but had no luck finding a free version of the paper. However I did find this fuller version of the article, with nice illustrations:
http://www.gps.caltech.edu/~oa/titanlakes.shtml

[volcanopele]

Very nice article! Thanks for the link. Though, hmm, there are a lot more empty lakes down in the south polar region than mapped...

[ngunn]

If the ethane content of Kraken Mare is substantial, then there's just no way to move it around

If the lakebeds are porous maybe the ethane doesn't have to move between hemispheres on either timescale. When evaporation concentrates ethane in a lake it may be able to diffuse into the less concentrated subsurface alkanofer. Methane diffusing the other way would return to the lake, ensuring that evaporation could continue until the lake appears dry. Of course on this model you have to move even greater volumes of methane around - to lower not just the lakes but the surrounding alkanofer too.

[Juramike]

Though, hmm, there are a lot more empty lakes down in the south polar region than mapped...

(I think so, too...a lot more. Topographical information for the S Polar regions will be really helpful.)

[Juramike]

Of course on this model you have to move even greater volumes of methane around - to lower not just the lakes but the surrounding alkanofer too.

True. But if the subsurface is extremely porous, you may only need to move a small percentage of the overall amount to effect a large change in the base level. Picture a 1 km deep porous bed: 10% change would give you 100 m change in solvent level (ignoring volume of porous material).

So while the absolute amount of methane to move from pole to pole is large, the relative amount compared to the (still unknown) subsurface reservoir could be fractional.

[ngunn]

Yes. And if the lakes 'breathe' into and out of that greater reservoir we have to think of them very differently from the way we think about terrestrial lakes. A closer terrestrial analogy might be dune slacks which are common near where I live. I'm not sure how current that term is but it refers to pools in depressions within areas of coastal sand dunes.

[rlorenz]

If the ethane content of Kraken Mare is substantial, then there's just no way to move it around on seasonal timescales. Oded's Milankovic timescales, maybe.

Right. Likely difficult to determine remotely (detecting that ethane is there is one thing, as for
VIMS/Ontario ; measuring an abundance is another thing. In principle microwave radiometry might
be able to do it (or RSS bistatic), might need assumptions about roughness or depth etc.)

Titan Mare Explorer will do a bang-up job on lake composition...

If Kraken is deep (as its size suggests it should be) it is hard to see that it could be seasonal, regardless of
composition.

I have been on a jihad for some time to stress Croll-Milankovich. James Croll figured it all out in the
1860s. Milankovich just came along later and did the astronomical math a bit better. (Croll I think was the
first to calculate how much colder Europe would be without the Gulf stream, for example ; he studied
boulder clays and geological evidence, as well as the astronomical forcing and heat budget.)

[remcook]

So, what is new in this paper? The speculation about the Croll-Milankovich cycle? (yes there probably is an effect and it is a valid hypothesis, but do we really see any evidence for it happening? Erasing craters at the poles are happening anyway, regardless of the cycle, since there is methane rain on either side, right? Plus, there might be other erosion mechanisms at work. Not sure you can tell from a dozen craters.) Didn't we already know that there are more lakes in the north, that the topography is similar and that the northern winter is harsher than the southern? Maybe someone can explain in a bit more detail?

[Jason W Barnes]

Titan Mare Explorer will do a bang-up job on lake composition...

Assuming that the lake really IS deep enough so as not to volatilize entirely and head south for the summer.

- Jason

[Juramike]

Splash, schplat, or crunch?

[ngunn]

Some thoughts on Ontario Lacus prompted by reading this paper:

It is unique - no other large lakes are observed in the south. It is located far from the center of the south potar regional topographic low. It is unlike the large lakes in the north in that valley systems converging on it do not appear to continue for long distances into the lake in the subsurface topography. Ethane has been detected in it and as the paper points out this is consistent with it having experienced a lot of evaporation to concentrate the ethane. Concentration of ethane implies no major exchange of liquid between the lake and a surrounding alkanofer (anyone got a beter word? - liquifer??). Maybe it's uniqueness is due to it being situated in a uniquely impervious basin.

Lots of questions. What special circumstances could create an unusually impervious basin? Are there any analogues in the northern hemisphere at the present epoch? How might they stand out from the methane-saturated crowd?

Just thinking aloud . . .

[marsbug]

Splash, schplat, or crunch?

Boing? It still might not be strictly speaking a liquid in those lakes- it might be a massive tangle of long chain hydrocarbons with pore spaces that fill up during the wet season and dry out at other times. It could be like a giant rubbery sponge!

EDIT: That wasn't meant in earnest, but this is: What are the odds of the material in ontario lacus haveing non-newtonian properties, like custard? Many polymer solutions do!

[rlorenz]

Boing? It still might not be strictly speaking a liquid in those lakes- it might be a massive tangle of long chain hydrocarbons with pore spaces that fill up during the wet season and dry out at other times.
....
EDIT: That wasn't meant in earnest, but this is: What are the odds of the material in ontario lacus haveing non-newtonian properties, like custard? Many polymer solutions do!

Well, Steve Wall has a paper submitted on Ontario with an interpretation of possible wave action on the shores, so
it was probably 'fluid' at some point, and likely is today. In the future it may dry up to the point where the mud
that is left behaves as you described, like, uh, mud, but you actually need quite a high volume fraction of suspended
material to give it non-newtonian behavior like a shear strength.

Now, you don't need that much suspended or dissolved stuff to increase the viscosity somewhat, and in fact
there is a big difference between ethane and methane viscosity. Ethane more viscous, add in a few per cent
of propane, butane and maybe Ontario shouldnt get waves today.

On the other hand, we've only observed Ontario in seasons when winds are predicted not to be high anyway.
Upcoming observations of northern lakes may be different

see (hot onto the presses)
http://www.lpl.arizona.edu/~rlorenz/viscos...es_accepted.pdf

[ngunn]

What a fascinating paper! Thanks for posting it here.