I hate to say this, try IE. Seems to work better there.

Just an advertisement for the talk I provided the most work for, Zibi Turtle's talk at 9:30am in the Titan Lower atmosphere session. I doubt you will be disappointed.

EDIT: That should be 11:30am EDT

Starting right now.

"Pretty cool" was an understatement.

The whole session was great. But with all that methane being convected and precipitated, large lakes with steep shorelines, extensive liquid-carved channels - why hasn't the VIMS team found anything deeper than a puddle?

I wasn't exactly sure of the argument of calling the areas "playas" in one of the presentations. I think most of the absorbance curves for depth calculation were generated assuming the bottom albedo was "1.0" (perfect mirror). I kinda think that is highly unlikely.

In a later talk, Lawrence Soderblom's presentation seemed to imply that the 5 micron (2000 cm-1) albedo of Ontario Lacus was nearly zero (no scattering at all, no reflectance). The strong absorbance of ethane at 5 micron means that very little would be required to zero out the spectrum. (Slide 239)

So I think it was the 2.0 micron absorbance (or lack thereof) that was used to imply a shallow lake depth, since reflectance is pretty much unaltered at this wavelenght. (Slide 246).

But this assumes that the surrounding terrain (non-lake) is at the bottom of the lake. (The lake has minimal effect on the 2.0 micron absorbance, thus it's not real deep). If the lake material contains "stuff" (suspended? lying near the bottom?) that reflects 2.0 micron radiation pretty well then the depth analysis doesn't hold water (!).

[2.0 micron is a water absorbance band local minimum, so all it would take to get better reflectance than adjacent non-lake terrain would be some "less water-ice"-like material. So any organic "non-water-ice coated sediment" could do the trick.]

The questions at the end of the presentation did ask about suspended or floating sediment or materials. "You can't judge the depth of Cayuga (a very deep lake in the Finger Lakes region) by what I can see at the surface."

I think a fair statement is that the hydrocarbon absorbance (derived optical depth) from lake reflection is minimal. Not sure whether this could be solely due to shallow liquid depth.


[I also noted that the 5.01 reflectance image shown in Slide 245 correlated nicely with the putative Deep Black unit (which was proposed from the possibly artifact-ridden 2.8/2.7 ratio). "Noise shouldn't correlate" ]

-Mike

-Mike

Yes, but the suspended material suggestion was countered with the question: what can stay afloat in liquid methane? (Not much.) Also someone made the point that fine material in suspension would be more transparent to IR than to visible light so it's that much more difficult to fool the IR with a 'false bottom' of suspended material.

In another presentation the case was made that the lake surfaces must be extremely flat, with no sign of wind waves, yet we know there are winds. Putting these two things together, I'm picturing a fluid more like black paint than petrol - difficult to make waves on and very opaque. The suspended material must be in particles small enough to be kept aloft by random thermal agitation, perhaps individual large molecules rather than 'grains'. Would that provide enough IR opacity? I haven't a clue! Perhaps you do.

Cue to admin: maybe we need moving to the Titan subforum.

What can stay afloat in liquid methane? Well, something less dense than the liquid - maybe something with liquid and air. For example (my favorite), how about a chunk of clathrate with gas-filled micropores? ("Cryopumice"). Or some type of frothy, foamy organic material. (BTW, foaming can be a MAJOR problem in large scale chemical plants).

What can stay suspended in liquid methane is probably a much easier question. Heck, I'm not even convinced that the hydrocarbon lakes have a low density (or viscosity for that matter). With your paint analogy, there could be some organic goop suspended around in a yukky organic mess. The whole lake could be a big emulsion (which could also change evaporation rates).

The key is that there needs to be IR reflection, at least in the 2 micron area.

Now the other question is: if the lake liquid is so thin, how come RADAR isn't able to penetrate it? Or is RADAR hitting an absorbing(diffusing) subsurface layer as well? (AFAIK, RADAR hasn't yet gone over Ontario Lacus, I'm extrapolating from the northern lakes).

My picture of a Titan lake is now of a flat, black, hydrocarbon emulsion/suspension.

-Mike

[Yup, I agree, the last few posts should be put over to the Titan subforum, probably the "Titan's Lakes Revealed thread", starting from VP's post #12]

Moving Titan lakes talk here

That was actually Jason Soderblom. He's Larry's son and my replacement as VIMS postdoc in Arizona.

- Jason W. Barnes

PS -- Yes, yet a third Jason.

Can't even say VIMS Jason anymore.

I didn't see a link posted for the DPS 2008 conference. Here is one that takes one to the schedule of presentations with links to the video stream and slides.
http://dps08.astro.cornell.edu/AAS_WebcastSchedule_2008.html

Worth mentioning the likelihood that there may be huge differences between lakes, and between seasons (especially for the smaller ones). A recently recharged lake may be runnier and more transparent (or maybe not!!). A lake which drains into another (overground or subsurface) may be very different from one that is a 'dead end'. I think there are just too many variables and not enough observations yet for a comprehensive synthesis, and that's exactly why it's all so fascinating.

I'm a great fan of floating foams and pumice in some situations, but they don't seem to help with the present puzzle.

I am not sure if this clarifies what you are asking, but click on the session 23 link for Sunday. This session has the presentations that are discussed in this forum.

See http://www.abstractsonline.com/viewer/viewSession.asp for a list of presentations. The relevant ones are the last four.

Titan ain't easy.... what fun!!!

Good Viewing!!!!!

Craig

http://www.unmannedspaceflight.com/index.p...mp;#entry128546



No such page...

Try the link I used last night. http://dps08.astro.cornell.edu/AAS_WebcastSchedule_2008.html
Seems to work fine.

Yep, that's the one from Emily's blog that was posted last week, I'm talking about the abstractsonline page which is coming up with an invalid URL error.

hmm, maybe direct links have issues?

Try: http://dps08.astro.cornell.edu/sciprog.html, then click on the "online program planner" link. From there, "Use Browse to explore lists of sessions and presentations."

The Titan Subsurface session just ended. The session had a number of talks on Titan cryovolcanic processes (or expected processes) that were quite interesting:

* Rosaly Lopes presented a talk on RADAR observations of Hotei Arcus. I can't wait to be able to see how the RADAR observations compare to some of our high resolution images acquired a few months ago. Okay, as I am typing this, that's what I am doing. Okay, Hotei Arcus, the bright arc of material seen by ISS, is the edge of the "cryoflow" terrain RADAR saw. Interesting correlations.
* Tortola Facula is.... a random piece of hummocky bright terrain, like all the other bright doo-dads in Shangri-la... no evidence for cryovolcanism in the RADAR data (let alone the VIMS data, where much more convincing evidence can be found in Tui Regio and Hotei Arcus).
* RADAR team moving full speed ahead on topo-from-SAR, with interesting results. Unimodal world (think Venus, not Mars or Earth) with a continuum of terrain heights of +/- 1 km.
* Possible ammonia-water ice found at Hotei Arcus from RADAR data.

OT for a 'lakes' thread but from the same conference session, an note about compressional tectonism on Titan, unique among icy moons. Secular global contraction does not produce tectonic folds with preferred directions. De-spinning can, but in the wrong sense for those observed. (It favours NS rather than EW fold ridges) We see EW ones, exemplified by T8 radar. A questioner made the point that we are missing something, and the speaker did not cotradict that. My suggestion is already on record here so I won't sound off again.

That was pretty surprising. Does this mean that it could have had a cryovolcanic origin, but then has equilibrated/gotten covered/eroded so that it now looks like normal hummocky bright terrain.

Extending this thought, is it possible that the normal hummocky bright terrain may all have looked like Tortola Facula at an earlier stage (could the little bright spots all be of cryovolcanic origin way back when?)

And yes, Sotra Facula is still one of my favorite spots on Titan...

-Mike

I don't see how the shallow lakes idea is consistent with the SAR results either. If the lake liquid (or the subsurface layer) isn't extremely radar absorbent, then it must be very smooth. How do you get a surface that smooth over hundreds of square km (for some of the larger lakes) other than filling it with of liquid? Some sort of semi-liquid muck covered by an veneer of liquid?

--Chris

"That was pretty surprising. Does this mean that it could have had a cryovolcanic origin, but then has equilibrated/gotten covered/eroded so that it now looks like normal hummocky bright terrain."

No. This is a classic case of overinterpretation. I have ranted about this elsewhere, like Skinakas. All we had was a little irregular shape. Somebody says 'hey, that looks like it might be a volcano' - and then every reference to it suggests it's a volcano. But there never was strong evidence, it was just a hunch. It could have been anything. What we need is a few more working hypotheses right from the start.

Phil

Tortola Facula and Sotra Facula have some morphological similarities. They both have a spiral indication when viewed using different intruments.

Tortola has a spiral shape in the ISS and VIMS data.
Sotra has a pronounced spiral shape when observed by SAR RADAR imagine (both T25 and T28).

Spectrally, they both look like Equatorial Bright terrain. (IIRC, Sotra Facula was observed at lower resolution in the VIMS but didn't show anything extraordinary).

[I need to dig for scatteometry and radiometry info, but I don't think there was anything special at either Sotra or Tortola.]

Neither looks like the pancake dome of Ganesa Macula, or the putative fumarole-ridden areas of T13 W Xanadu or Hotei Arcus.

My personal model right now is that the Equatorial Bright terrain is the original crustal material - either the stuff that came up from the crust, or stuff that has come up from the crust and had time to equilibrate with the atmosphere (whatever timescale that is).

I'm not sure what an ammonia-water cryovolcano would look like on Titan. Or if it is possible that there are different flavors of cryovolcanoes on Titan (cryo-stratovolcano? crustal-material volcano? some types of cryo-dikes or cryo-pluton? collapsed cryo-pancake dome and revealed internal structure thingy?)

Nor do I know what and how one of the above features would erode or evolve on Titan. Deep incisions to become further crennelated? Exfoliations to become even smoother? What sort of spectral modification will happen over time?


In a stretch (my speculation) Sotra and Tortola Facula might be related to some of the brighter hummocky Equatorial Bright islands. (spectrally similar, some similarity by RADAR, but Sotra (and maybe Tortola) morphologically rougher (= younger??).

But they are very different from the fumarole areas of T13/Hotei Arcus (spectrally and morphologically).

I wouldn't say that Sotra and Tortola Facula are "not cryovolcanic structures", but I don't see any spectral or morphological evidence that relates them to either Ganesa Macula or the fumarole areas.

(And I'm not sure at this point what additional data from Cassini could be acquired that would shed light on the history of either Tortola Facula or Sotra Facula. Except perhaps higher res VIMS over Sotra and hope something lights up.)

-Mike

It was nice to see the map with improved ISS coverage actually showing the north polar dotted lake district that we've seen mainly on radar before. Which set of images was this from? Could this be from Rev 72? This was in Zibi's talk that VP Jason mentioned.

Steve