I am trying to post the VIMS image of the bottom right end of the lake but spectacularly failing - either to copy or attach it, so this is the best I can do.

Go up to post 48, open the Barnes paper and scroll down to page 5. There I think you will see the islands near the mouth of that river that also appear in the SAR, along with a caption outlining the VIMS team's interpretation of the shoreline features. At first glance the VIMS data and interpretation dovetails fine with the ISS/RADAR story.

I think the ISS/VIMS/RADAR story is coming along nicely. It definitely seems clear that the observed paucity of lakes in the south and the abundance in the north noted by RADAR seems to be due seasonal bias: the north is in its wet season, and thus has more filled lakes, while the south is it its dry season where the lakes generally dry up (temporary fillings due to storms not withstanding, as seen by ISS 2004/2005). By the end of the XXM perhaps we will see the opposite pattern, an abundance of filling lakes in the south, and shrinking lakes in the north. Kraken Mare may slowly become a mudflat, and Mezzoramia "Mare" may become the great southern sea.

Link from remcook:

http://www.sciencedirect.com/science?_ob=A...9c22eeb4cd844bd

The abstract contains the statement that the lakes fill up due to precipitaion in summer and dry out by evaporation in winter. Any comments?

I guess my comment is that I think they have it backwards...

HA! Check out my post in the SAR 48-49 thread, post # 6 placed on Oct 3rd. I showed the same change in the lakes comparing the T36 and T49 overlap region as is discussed in the second paper in Olvegg's post above! While I thought the change from radar dark to radar bright in the floor of these small pothole lakes or calderas might be a seasonal drying up effect I wasn't really sure. This seems to be the radar teams reasoning as well.

How wide is thay channel where it appears to open out into the lake?

So, the next probe may not choose the north polar lakes or seas for its landing site!

Indeed, Mezzoramia may become the Kraken Mare of the south polar region.

The Huygens probe may become a wreck in the depth of the potential sea which is likely to take shape as the giant ethane cloud ( currently engulfing the north pole) migrates toward the south.

The landing site might depend on the season when the boat would land yes, but I think what is perhaps most clear is that we need to observe Titan over more of its year before we take even what I said as gospel truth.

As far as the fate of Hugyens, keep in mind that the ethane cloud doesn't literally migrate. As spring progress it will likely just fade in the north and form up in the south rather than actually moving between poles.

Hmm. It does seem as if the 'desert' equatorial regions get some gully-washer storms, though. Huygens sure looks like it's sitting in a flood channel...maybe an arroyo?

Would expect such storms to start popping as the season change progresses, if they happen with any regularity at all.

Yeah, and storms are not unheard of at the latitude of the Huygens probe, but not that giant ethane cloud at the north pole.

Gotcha. I'm definitely thinking flash floods are possible in Huygen's neighborhood, but not long-term standing bodies of liquid.

It seems ages since I posed the question: Where is Curien Station? Is it for once and all the latitude and longitude where the probe landed, or does it move when Huygens gets washed along a bit, maybe even buried? (The first option is itself problematic as we now know, due to the variable rotation state of Titan's floating crust.)

I think a typical surmise just now would be that at any given tropical location floods are more like millennial events than seasonal ones. The changes now unfolding at high latitudes are exciting enough but, as VP points out, we need to watch for a few years more before anyone can do more than make informed guesses about the big picture. That's what's so great about this amazing active world. Everyone has a ringside seat at the show and nobody knows what may happen next.

Here's my shot at Fig 2b trying to zero near the "Spooky Dude" formation.
From: Jaumann et al. LPSC 40 (2009) Abstract 1599.

Click to view attachment

Graphic is of Fib 2b masked and infilled with a hue/saturation adjusted and contrast adjusted and Gaussian blurred [0.5 pixels] Fig 2c - Fig 2a (after masking line & text area and underfilling with vortex-modified Karoschka mosaic).

Looking forward to the full article....

[EDIT: Even with this hack job, one can see that the R1, R2, and R3 balance out to the correct colors. So if the Spooky Dude formation is in the VIMS, it could be either R1 (bright region terrain) R2 (blue region) or something else that spectrally resembles either of those. R3 (brown region = dune material) can be safely ruled out.]

Some posts have been removed from this thread, as they contained links to and images from data that should not yet have been in the public domain.

Check out Photojournal http://photojournal.jpl.nasa.gov/targetFamily/Saturn from today. Posted are two superb figures that were presented by Alexander G. Hayes at the Division for Planetary Sciences meeting of the American Astronomical Society on Oct. 6, 2009. Olvegg has posted the links to the presentations earlier in this thread (post #49).

VIMS sees specular reflection from Kraken Mare:

QUOTE:

After more than 50 close flybys of Titan by the Cassini spacecraft, it has become clear that features similar in morphology to terrestrial lakes and seas exist on Titan’s surface. Widespread evidence for fluvial erosion, presumably driven by precipitation of liquid methane from Titan’s dense atmosphere is also apparent from these data. Lake-like features have thus far only been observed in Titan’s polar regions. Of these presumed lakes, liquids have only been conclusively identified in Ontario Lacus, a relatively small lake in Titan’s south-polar region. As Titan progresses into northern summer, the much larger lake-like features in the north-polar region identified in Radar data, are becoming directly illuminated for the first time since the arrival of Cassini. This allows the Cassini optical instruments to search for specular reflections to confirm the presence of liquids in these presumed lakes. On July 8th, 2009 the Cassini Visual and Infrared Mapping Spectrometer (VIMS) successfully detected a specular reflection in the north-polar region of Titan. The signal is restricted to the VIMS channels at ~5 µm where most of the incident light reaches the surface without being scattered by aerosols in Titan’s atmosphere. By mapping these observations onto the RADAR image from the T19 flyby, the VIMS specular reflection was found to be associated with the western part of Kraken Mare, one of Titan’s large northern lakes, indicating the lakes surface is mirror like, strongly suggesting it is liquid.

(with thanks to 'Gish Bar Times' for the link to these abstracts).

And there's so much more - here:

(struggling to post a link that works)

http://agu-fm09.abstractcentral.com/planner.jsp

OK that works. Now: Browse / Friday / Planetary Sciences and you're there.

Personal anecdote: perhaps not many people remember their 57th birthday as one of the best. I do. Not only did we have this VIMS observation of northern lakeshine, but also the Ontario SAR:



The SAR of Ontario Lacus was long expected and advertised, but the VIMS Kraken Mare specular reflection was not mentioned in the July 8 Mission Description or in the 'Looking Ahead'. I wonder if it also was expected, or purely serendipitous?

Another morsel from the conference abstracts. Anything to do with timescales on Titan always grabs my attention. This one was hiding outwith the dedicated Titan sessions. Because of the difficulty of linking to these abstacts I'm going to try posting a series of short QUOTES from:

Geomorphic Analysis of North Polar Channel Networks on Titan, and Implications for Active Tectonics and Persistence of Relief Structures
R. Cartwright1; J. A. Clayton

"Assuming constant 1.5 m depth liquid hydrocarbon flow during the summer (wet) season, we estimated that roughly 19,800 Titan years are required to lower Basin A down to its minimum relief."

"recent tectonic uplift could help explain why this region displays variable relief, as well as contorted and constricted channel networks"

UNQUOTE

If I understand correctly this implies that typically the relief confining Titan's lake basins only formed within the last million (Earth) years or so, or else the basins are continuously deepening themselves at a pace that matches erosional degradation of the topography. The timescale tallies quite well with the ages of terrestrial lakes, relatively few of which go back more that a million years.

Gosh I hadn't realized the word was out yet. I guess if AGU abstracts are published then there's a good reason for the leakage . . .

- Jason

Catching the lakeshine:

Radar 21st December '08 - VIMS 8th July '09 - Go ISS!

Considering we only saw it at 5um, and not at 2.8, 2, 1.6, 1.3, or 1.1, I think that ISS is going to have a challenge finding it at 0.93um.

- Jason

Yeah, you caught the sun's direct reflection at a pretty oblique angle, right? A very spectacular result - I look forward to seeing the crucial image when it's published. I realise the haze makes that impossible for ISS but I'm still hoping (until I'm told otherwise) that they may be able to identify specularly reflected skylight near the Brewster angle.

I guess if those are the only two options, then it's "serendipitous". We have been looking for specular reflections all the time, but haven't seen any -- the reason of course is that the Sun hasn't been shining on the wet places (Ontario excepted). So while we look at the images and keep specular in mind, we haven't before designed a sequence around it. Now that we've found one and see how totally cool it is, though, and what great science can be done with it, we're looking for opportunities in the future to do a planned specular campaign. It all depends on the spacecraft geometry, though, so we pretty much just have to wait for the right time.

- Jason

Thanks, Jason. Congrats to the team and good luck with future targeted lakeshine studies.

As I've remarked to you in person, it is totally cool. But what is the great science ? Since the specular point
is just that at any given instant, the geometry varies with time (i.e. the angle varies as the point tracks across
the surface, so you don't vary angle and position independently [this is also a problem in the radio equivalent -
the bistatic scattering experiment, results of which from T12 years ago have yet to be published] - maybe it's
not too much variation, I guess may depend on the specifics of a given observation.) If you
can resolve the brightness distribution around the specular point, then it is an interesting measure of roughness
across an assumed uniform structure like a lake, although is it any better than a SAR image of the same thing?
But a single pixel specular reflection is of limited utility, I think....

Not to be a (shiny) wet blanket, and I repeat, it is cool, but by itself it isnt telling us a lot about Titan unless I am
mistaken.

Excuse a very basic question: would that be one pixel at one wavelength or do you get an IR spectrum for that pixel?

Each pixel is being observed at the VIMS IR wavelengths. So, in theory, you'd get an IR spectrum for each pixel location. In practice, the methane absorptions limit how many wavelengths you could observe, then atmospheric scattering makes some of those wavelengths (esp. the shorter ones) difficult as well.

Somebody's gonna have fun applying all the atmospheric and haze corrections to get the corrected spectra.

It'll only be close to a "perfect mirror" at a few select wavelengths due to the intervening atmosphere. Kind of fun to imagine a funhouse mirror that would only reflect "blue" and "orange" but nothing else.

I was thinking this kind of observation could be a powerful means of quantifying those things, thereby sharpening up the interpretation of other VIMS data, especially the remainder of the same image.

You are mistaken.

Saying that there's no information to be had from a single pixel would imply that, for instance, transiting extrasolar planets would tell us nothing, since they're just one pixel. In fact this is an apt analogy. I approach the Titan problem from the exact same standpoint -- that of a lightcurve. I fit the lightcurve using various critical parameters, from which I get the science. For instance, the lightcurve tells you the path that the specular reflection takes (using the RADAR basemap), from which I can infer the triaxial shape of the equipotential surface, along with other cool things like wave properties and the composition (okay, index of refraction) of the fluid. Stand by for the paper, it will probably be a few months yet with my twin babies arriving soon, but I think that by the end you'll agree that your above statement is one-minus-correct, perhaps not unlike your 1996 no-sand-dunes-on-Titan paper!

- Jason

Well, there's a spectrum all right, but as the AGU abstract states, the specular reflection has no effect on the wavelengths shortward of 5um. So there's a spectrum within the 5um window, and upper limits below that.

- Jason

Wot, are you a graduate from the Roger Yelle school of diplomacy or something..?



Hmm, well, I'll stand by for the paper. But I still don't see how you can get wave properties and
composition independently for each point on your lightcurve : I can see how you might derive one
value for each if you assume the properties are spatially uniform along the specular track,
which they may or may not be (as casual inspection of a resolved image of sunglint on a terrestrial
lake or sea will tell you)

In any case, I hope this is just the first of many cool VIMS lakes results in coming years as the sun
rises over Titan's north. Hopefully the sunshine won't kick up too many clouds that you cant see anything..

Well, that presumes a single image of sunglint. Multiple images showing how the reflection changes with phase angle would help.

Titan's like Kansas. The skies are never cloudy all day.

Agreed that there can't be composition and wave gradient distributions for each datapoint. But the composition of the lake should be the same for the whole lightcurve from mixing presumably, and if you assume a lower-order fit to the waves as a function of position, then you should be able to pull out some variations. Not from the present 4-point T58 lightcurve, mind you, but from potential future, tighter observations.

Also note that I would say that this technique has an advantage over the Wye et al. technique in that it does not require valuable closest-approach time -- the observations in question were a few hours after C/A IIRC.

- Jason

Edit -- Not to knock the Wye et al. work, which I think is awesome! Just that watching lakes looking for variations in waves would be expensive in terms of C/A time using that method.

Article on seasonal and longer term change:
http://www.sciencedaily.com/releases/2009/...91129153401.htm

Source paper:
http://www.nature.com/ngeo/journal/vaop/nc...bs/ngeo698.html

We shall see. I still think its seasonal.

But then where are the empty south polar lakes? Does the whole south pole fill up in southern winter? This is a problem with both the seasonal and longer-term migration of volatiles. I think that the total volume of methane/ethane transported between poles over seasonal and longer timescales is small, and that Kraken stays pretty much the way it is year-round.

Maybe.

- Jason

Where are the south polar dry lakes? What do you think those low, flat areas are in the RADAR sar data that match up with ISS dark areas? That being said, the north polar region seems to have more dedicated lake basins while the south pole has mostly opportunistic playas (though there are a few of those up north too).

As for Kraken Mare, again, I think it is still plausible that Mezzoramia is the south polar version of that sea.

I don't have access to the full paper, but from what I have seen I like the idea of seasons superimposed on 'superseasons'. Nevertheless there must be other major factors involved as well, regional topography being an obvious one. For me the fact that there is still legitimate room for widely differing opinions on such a major matter is humbling and quite wonderful in itself.

I think they're dark areas. They could be anything.

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.

- Jason

PS -- I can't even get a copy of this paper -- I guess we're not subscribed to Nature Geoscience here for some reason?

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

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

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

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.

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

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.

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.

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.)

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?

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

- Jason