[X] My Assistant

[Exploitcorporati...]

Here is a manual stitch of forty screencaps from the quicktime movie in an attempt to show as much of the lake district as possible. Rectangular gaps are due to areas missed in the movie's zig-zag simulated flyover. The T18 swath was not shown in detail and is excluded.




EDIT: T19 swath patched with familliar PIA releases. Images and movie courtesy NASA/JPL.

[Exploitcorporati...]

Some fun with perspective views:

[nprev]

Cool to the nth power...thanks, E!

Notice the lakes in the center of the top-most perspective view...there's a very linear raised ridge that is interrupted by a couple of lakes! Obviously, then, the lakes formed after the ridge, but how? They don't look like filled impact craters...are they collapse pits from the local "aquifer"? If so, they may be much more permanent than currently thought...

EDIT: Circled the area I'm talking about on Exploitcorporation's image:

[Exploitcorporati...]

It certainly does seem like there's a lot of visible topography in this area, but with these RADAR images, I'm never sure. Something about 600m walls around these lakes in another thread...really looking forward to increased coverage of this region on future passes, in addition to eventual ISS imagery. I love this moon, and especially love the puzzle-piece buildup of data, one flyby at a time. Reminds me of those goofy Advent calendars I had as a kid...or that life-size cardboard cutout striptease in either Bull Durham or Major League...I can't remember which. I think I may have just reduced my apparent IQ...

EDIT:nprev, are you referring to the vertical line (in this view) in your highlighted area? If so, I think that's an artifact of the imaging process. If it's the horizontal feature, I think I see what you mean.

[Olvegg]

Great work, Exploitcorporations!
I use your image to update my previous map. This time without future swaths, 0 degrees WL is to the right:

Attached thumbnail(s)

 

[ngunn]

Thanks for posting those images. I'm on my daughter's computer at home which irritatingly won't let me open the NASA links. I was just going to say the 'ridge' pointing at 1 o'clock in the circle looks like an artifact as it aligns with similar ones further up, running parallel to the edge of the swath. However there does seem to be another entering the circle around 2 o'clock which appears to form a little 'headland' jutting into the lake. It's great that we're going to get good topographic information for parts of this area. There are sure to be lots of surprises. Could the lakes form their own raised edges by precipitating some dissolved material each time the margins dry out? Exciting times!

[nprev]

exploitcorporations wrote;

EDIT:nprev, are you referring to the vertical line (in this view) in your highlighted area? If so, I think that's an artifact of the imaging process. If it's the horizontal feature, I think I see what you mean.

No, the vertical one. If you look closely, the ridge curves to the right a bit on the lower side of the "bottom" lake. I don't think this is an artifact, since it's clearly interrupted by another lake as well. In fact, a little further down from there there is a small hill that looks as if it might have been part of the ridge at one time.

Sort of looks like the eroded remains of a Europan ridge to me in some ways...maybe there are some similar processes at work.

[Exploitcorporati...]

No, the vertical one. If you look closely, the ridge curves to the right a bit on the lower side of the "bottom" lake. I don't think this is an artifact, since it's clearly interrupted by another lake as well. In fact, a little further down from there there is a small hill that looks as if it might have been part of the ridge at one time.

Okay. Now I see it. I can't wait for the DEMs of this area.

Olvegg: Excellent!!!

[alexiton]

Howdy,

Good stuff guys, too bad that in my haste I so wantonly erred (hence this massive edit and pictorial retraction). Oh well, only month or two until SSP and DISR data becomes PDS goodness...

Cheerio.

[ngunn]

Another thought on the 'lake district'. I'm not convinced that every topographic low in this area contains a lake and all the intervening regions have drainage leading to a lake. So what happens to the rain that falls in between? If it doesn't drain into a lake does it just soak into the ground? In that case the lakes would not necessarily be in the lowest places, but rather in locations where an impermeable layer happens to exist to act as a lake bed. That could be why they seem to like forming in caldera-like structures. Some of them may even be on hilltops. We shall see . . .

[nprev]

Yeah...I've been thinking of them now as basically sinkholes, something like you see in Florida. The ground is so saturated with methane that some areas with locally loose surface materials collapse into lakes that are at least initially at the level of the local 'methane table'.

Of course, this is Titan, so a whole lot of other things are also possible. Still, exciting, interesting stuff!

[dvandorn]

I'm not positive about that sinkhole theory, nprev -- looks to me like many (if not most) of the lakes occur within the walls of circular depressions, but it also looks like they fail to fill the entire depression in most cases. Looks more like they might have entirely filled the depressions at some point, but have evaporated down to remnants at this point.

The depressions look more like old impact craters than calderas to me, but that's a hard distinction to make with the resolution that we have.

-the other Doug

[nprev]

Oh, neither am I; this hypothesis is just a WAG based on terrestrial analogs. My impression is that most of the lakes have polygonal/fractal rather than circular geometries, which to me suggests some sort of local crustal collapse instead of a "punchbowl" impact alone. However, each of them may well have started as an impact crater, which subsequently was modified by "groundwater" effects (we really need to develop some new terminology, here... ).

[Thorsten]

Kudos to Exploitcorporations and Olvegg – this is great work and it allows some early and wild guesses. Looking at the two swaths I would assume that ~ 5% of the revealed surface, north of 70°N, is covered by features that are radar-dark enough that I would confidently call them “lakes”. If we assume – just for the sake of this speculation – that this would be more or less representative for the whole Land of Lakes (north of 70°N), we would have ~ 125 000 km2 of lake-covered area of a total area of ~ 2 500 000 km2. Put in one lake this would be larger than Lake Michigan and Lake Huron together (117 000 km2). If a similar fraction of the south polar area would be lake-covered, the total area of lakes on Titan would be 250 000 km2 or two-thirds of the Caspian Sea (375 000 km2), or 0.3% of Titans total surface area (83 300 000 km2).

Mitri and co-workers (Mitri et al., 2007) have assumed that evaporation from lakes covering 0.2% - 2% of Titans surface would be sufficient to buffer the atmospheric methane’s relative humidity at its observed value. Of course, these speculations are highly dependent on many variables, (such as the percentage of ethane and higher hydrocarbons in the lakes). However, by the end of this year (T39 flyby, December 20, 2007) we should at least know a little better the surface area coverage of the South Polar Lakes.

[Mongo]

I don't have the exact area for Ontario Lacus, but it is apparently similar in size and shape to Lake Ontario (about 18,000 km^2), which does agree with its long dimension of about 235 km. This single lake would contain about 7% of the total south polar area covered by lakes, if your thoughts are correct -- which do sound reasonable to me.

I have no idea of the degree the south polar lakes have been reduced in area via evaporation, though. The rate of evaporation would certainly be higher right now than in the north polar region, but given the large cloud system seen over the south polar region at the beginning of the Cassini campaign, the lakes might have been 'topped up' at that time. It seems possible that there are two 'monsoon seasons' in the Titan polar regions -- one in local summer and the other in local winter. For all I know, the composition of the rain might be different between the two monsoons (i.e. ethane content) -- which, also considering possible differential rates of evaporation in a multi-component fluid mixture, could mean that the composition of the lakes varies over the course of Titan's year. There might be a vague similarity to lakes in Earth's deserts, which show considerable variations in salinity over the year, depending upon the current volume of water.

Bill