Printable Version of Topic
Click here to view this topic in its original format
Unmanned Spaceflight.com _ Titan _ Titan's "Lake District"
Posted by: Stu Jul 26 2006, 01:59 PM
With an hour or so to kill before heading out to work I thought I'd have a play about with the images of the "lakes". Having read that it might be possible to enhance these or future images to bring out more details - maybe even waves - I just started playing about with contrast and brightness, seeing what popped out... and just doing that shows detail and some features within the "lakes" which I'm interested in people's comments on.
http://img.photobucket.com/albums/v509/cumbriansky/lakes-detail.jpg
Now, before anyone tells me off for my "playing about" and points out, rightly, that you can't just take these raw images and pull info out without a LOT of work, please bear in mind I KNOW all that, okay? 
I'm no Nix or Nirgal or Horton, and I'm not suggesting this means anything, I'm just curious what I might have seen. I know the features might just be imaging artefacts, but... oh, just take a look and see what you think. I'm just pushing the ball down the hill here, not making any claims. I would be interested to hear what others think tho.
Sticking my neck out here, to me it looks like the "drainage channel" on the lower right hand side actually continues into the "lake" for quite a way, maybe even flowing beneath an "island" of some sort. Other things look like they're in there too, but I'm just wondering if the "lake" is actually very shallow and we can see channels on its floor...
http://img.photobucket.com/albums/v509/cumbriansky/lakes-features.jpg
...but heck, what do I know...
Posted by: ustrax Jul 26 2006, 02:05 PM
Well...It looks like an abyss to me... 
Edited: Now, "seriously", it's incredible the detail on the 'lake' shoreline...it looks like coral reefs...
Maybe Titan will be the one... 
Posted by: climber Jul 26 2006, 02:09 PM
Stu,
I understand what you mean and I like this. Remember when you show us those "gullys" in VC?
.I see what you see too but, well, I'd like to hear about the specialists. I have also a general question about the images (easily visible on your's) : what are the parrallel "stripes" that show pretty well over the lake?
Posted by: um3k Jul 26 2006, 02:29 PM
Here's my version of the image. The vertical stripes, which are imaging artifacts, have been removed by using a Fourier transform.
|
Posted by: Phil Stooke Jul 26 2006, 02:30 PM
I agree with stu - these are not artifacts. Check out this version too:
|
This can't be a body of liquid unless the radar can penetrate liquid hydrocarbons enough to give weak reflections off the bottom.
Phil
Posted by: Stu Jul 26 2006, 02:32 PM
VERY nice Um! Thanks for that. Love the detail visible on the shoreline...
I'm thinking now these interior featueres might be evidence that these lakes are transient features... they fill up, shrink back, leaving just channels on their floors to transport the liquid down to the lowest points in their centres, then they fill up again, the channels get re-covered and voila, we have a lake again...
Off to work now so I'll look forward to much more expert input than my own when I get home tonight!
Posted by: JRehling Jul 26 2006, 02:58 PM
I'd like to see a polar cartographic projection of this data. I wonder if we're just seeing patchy lakes at 80N while things get wetter on towards the actual pole. Roughly speaking, if you stacked three of these strips one atop another, the top of the third would be at the pole.
Remember that we're looking at a place that hasn't seen daylight in about a decade. Also note that we've known of rains at the summer pole, but we're looking at the winter pole. Is there a wet season/dry season? Or two wet seasons at each pole? Or one continuous wet season? This may be the wettest time of year here or it may be the dryest.
I don't think we can yet rule out that there could be a winter ice cap at the pole... this isn't winter, BTW, and it won't be winter solstice at the other pole until 2017. If the temperature bottoms out after that, we won't know it til the next mission: Cassini is probably not going to live long enough to see solstice unless its operations are budgeted very, very carefully to keep it pretty much dormant and conserving propellant until a "solstice" mission could take place.
Posted by: Sunspot Jul 26 2006, 03:04 PM
I always assumed the black kidney bean shaped features were the lakes rather than the feature referred to in this thread?
Posted by: MarcF Jul 26 2006, 03:37 PM
The whole region looks like a big methane marsh with more or less deep ponds (if of course liquid is indeed present and if this liquid is methane).
Do we know how deep the radar can penetrate throught liquid methane (or any other liquid) in order to evaluate the possible minimal (or maximal) depths of the putative ponds ?
Posted by: paulanderson Jul 26 2006, 04:00 PM
Phil
The Space.com (AP) article mentioned several of the lakes being dried up, but others apparently containing liquid:
Researchers counted about a dozen lakes six to 62 miles wide. Some, which appeared as dark patches in radar images, were connected by channels, while others had tributaries flowing into them. Several were dried up, but the ones that contained liquid were most likely a mix of methane and ethane. "It was a real potpourri," said Cassini scientist Jonathan Lunine of the University of Arizona.
http://www.space.com/scienceastronomy/ap_060725_titan_lakes.html
From the New Scientist article:
Earlier images from Titan also showed dark patches that were considered possible lakes, but they were less dark. "In this case it is much clearer. The contrast is so great that there are few doubts that the surface is a liquid one," says Enrico Flamini of the Italian Space Agency in Rome, a member of the radar instrument team. The new evidence is quite strong, but the case is not quite closed. These patches could still just be areas of soot, or dry lake beds. Imaging the area again could show if the lakes grow or shrink – and possibly even reveal waves.
http://www.newscientistspace.com/article/dn9612-titan-may-be-a-land-of-lakes-after-all.html
Perhaps these lakes are in various stages of evaporation, some dried up for now and some still filled with liquid?
Posted by: elakdawalla Jul 26 2006, 04:13 PM
Here's an example of a dried-up lake. I was trying to figure out exactly what kinds of features Rosaly Lopes and Karl Mitchell were talking about when they were talking about possible calderas. I sent this doodle to Karl, asking "I'm wondering if there are features in the press-released chunks that look like collapse features that _don't_ have liquid gathered in them. For example, if you look at the top swath chunk, at the west end, I think I see something that looks like a topographic depression that's not filled -- am I interpreting the sense of illumination correctly? (I attach a quick and dirty map to show what/where I'm talking about)
|
Karl replied, "We saw that depression too and discussed it for a while. A popular theory is that the lake was larger at some time in the past, and that the depression you mention evaporated (because it was shallower) or drained into the remaining body. I keep thinking of the Aral Sea as a possible analogue. The dichotomy between the pale and dark depressions seems to support the "dark = liquid" hypothesis. The "calderas" I'm looking at are much small and steeper-rimmed...." The rest of what he had to say I put in my http://www.planetary.org/news/2006/0724_Cassini_RADAR_Reveals_Lakes_on_Titan_At.html.
And yes, Sunspot, the telltale lakes are the ones that look kidney shaped; they seem to be in a variety of states of wet / drying / dried up, at least that's what the team is saying. If they are, in fact, lakes.
--Emily
Posted by: paulanderson Jul 26 2006, 04:48 PM
Very good, thanks for this, Emily. And excellent article, too, I had already blogged it yesterday.
Posted by: David Jul 26 2006, 04:50 PM
My impression now is that Titan has some but not a lot of surface liquid, but that there is evidence that Titan was wetter in the past and had more widespread surface liquids.
If this is so, it raises the question, when was the wetter period, what is the timeline of the drying-up, is the process linear or cyclic, and what caused the current drought? I realize that most of these questions are not currently answerable, but I wonder if it's at least possible to answer within several orders of magnitude: is the time one has to go back to find wetter conditions on Titan closer to 5 years or 5 million years?
Posted by: Phil Stooke Jul 26 2006, 05:27 PM
This version of the new image is a bit easier to interpret in darker areas.
Phil
|
Posted by: AlexBlackwell Jul 26 2006, 05:29 PM
Nice work, Phil.
Posted by: David Jul 26 2006, 05:34 PM
I can now see not one but three channels running right-to-left through the greater part of the dark "lake" in the upper right of the top radar image. If there's a lake there, it would seem to be much smaller than the entirety of the dark spot.
Posted by: Matt Jul 26 2006, 06:24 PM
It looks to me as though much of the detail within some of the lakes, especially the one you discussed first, could indeed be submerged topography and the beam is penetrating the shallower areas. I really get that impression with the first one and the one that resembles Crater Lake.
Posted by: JRehling Jul 26 2006, 07:27 PM
Another possibility is that the lake levels vary over time and the "sort of dark" areas aren't under liquid now, but often are, so they consist of mud plus rocks -- like the Huygens landing spot. Darker areas have more mud and fewer rocks and lighter areas have less mud and more rocks. Of course, the very darkest areas could be standing liquid or simply a very smooth mud surface.
These two interpretations of the dark-light continuum may both be at work, either from one feature to another, or both at work in the same feature.
Posted by: tty Jul 26 2006, 07:59 PM
Might not the radar penetrate to some extent in liquid methane? The main reason radar does not penetrate into water is that it is an electrical conductor (unless distilled). Anybody know anything about the electrical properties of liquid methane at 90 degrees absolute?
tty
Posted by: hendric Jul 26 2006, 08:33 PM
What's up with that lake in the middle of the top part of the swath? Is the straight wall an instrument artifact? I didn't see any comments on it. Also, the lake on the far right end of the swath at the top as a really "high" looking wall on one bay.
I see this kind of wierd, unhappy ghost-face on the left side; anyone else notice it? It looks kind of like a giant, ugly, unhappy bull. Man, I need to get out more.
Also, on both the top and bottom halves of the swath, doesn't it look like there is a basin in the bottom half?? The top half especially, it almost looks like those lakes are sitting around a central peak towards the bottom.
Posted by: ElkGroveDan Jul 26 2006, 08:37 PM
What would account for the "smooth" data then? Some kind of exotic tule fog?
Posted by: Phil Stooke Jul 26 2006, 08:45 PM
I meant the specific dark spot in that illustration, which was replying to another post about the same specific dark spot. If there are other dark spots which are truly smooth and featureless, they could be liquid. The mottled, channelized dark spots like the one I illustrated can't be liquid unless the radar is passing through it.
Phil
Posted by: Betelgeuze Jul 26 2006, 08:52 PM
I added bump maps made with the original image, to make some of the features more visible:
http://xs304.xs.to/xs304/06303/titanlakes2.jpg
I wonder what that strange feature in the red circle is supposed to be, a dried up channel maybe?
Posted by: David Jul 26 2006, 08:58 PM
What exactly does the bump map do? Add an artificial texture whose ruggedness corresponds to the brightness of the radar image?
Posted by: David Jul 26 2006, 09:03 PM
Perhaps we're looking at heavily eroded cratered terrain.
Posted by: Betelgeuze Jul 26 2006, 09:04 PM
Yes exactly, its using the image as an heigthmap. I know it shouldn't be used as a heightmap but it makes some features 'jump out' of the image
Posted by: Richard Trigaux Jul 26 2006, 10:03 PM
The electromagnetic properties of hydrocarbons (at ambient temp, but at low temp it must not be very different) are about 2-3 for epsilon zero, and 1 for mu zero. I don't remember the formula to derive the wave velocity in this, but it may be a square root, giving a velocity in the 200 000km/s, which is also the velocity in cables insulated with materials like polyethylene. This makes an optical refraction ration about that of special glass like crystal. This is not very high, and we can assume that, when the radar wave meets a methane-ethane surface, a fairly part of it penetrates into the liquid, provided that the surface is calm, with no waves, probably a common condition on Titan. (Eventually a patch appearing dark one day and clearer another time would be a tell tale evidence of waves, and thus of liquid). After, the radar wave can penetrate deeply into the liquid, which probably contains little particules to absorb it. If it contains, the patch will appear much darker. After, the reflection on the bottom gives an image of it, that the radar can get. We can imagine the result with a lagoon and no waves: features on the bottom are visible at depths of more than 10m. And methane is much more transparent to radar waves (similar bodies like polyethylene are used as insulators in high frequency cables, and even as wave guides).
So we can figure that methane lakes would appear as darker patches. But Huygens seemingly landed into one such patch, and it was not liquid. So it is difficult to infer that all dark patches are liquid.
Seeing the bottom of lakes is likely too. deep lakes should appear completely black.
About the geometric features on the image, they are very difficult to interpret. They more or less ressembgle features seen on earth wet polar regions, where, by some process, repeated frost and thaw create many circular lakes. But this interpretation don't hold much on Titan. This region indeed look like a swamp, and, as in certain Earth swamps, we observe many sub-circular features which could be mud diapirs.
Posted by: Bjorn Jonsson Jul 27 2006, 12:42 AM
Interestingly, extreme processing in an attempt to reveal details within the dark areas ('lakes') reveals that they appear different:
|
This is the big lake previously discussed. Some details are visible, for example I'm sure the 'channel' extending from the lake's lower right and into its central area is a real feature. Compare this with the following:
|
This is the fairly big 'lake' in the upper left corner of the original T16 swath. Interestingly, no details are visible within this lake. It may also be of interest that this lake appears a bit darker than the big one in the unprocessed original image. From the discussion above this could mean it is deeper (if this is a lake), wetter/smoother/more muddy (if this is not a lake) or this could be a processing artifact and not a real difference.
These images were smoothed a bit with a median filter, then greatly sharpened and then smoothed a bit with a median filter.
I would be very interested in knowing which software you used to get rid of the stripes with a Fourier transform. The Cassini ISS images contain noise (stripes) which is hard to get rid of and annoying in some cases.
Finally I should note that I'm attaching these images in PNG format and not JPG. PNG files are sometimes smaller than decent/high quality JPG files for high-contrast, high-frequency scenes like these. Also they are losslessly compressed, unlike JPGs.
Posted by: um3k Jul 27 2006, 12:51 AM
I used this Photoshop plugin: http://home.planet.nl/~ber03728/4N6site/improc/fftplugin/main.htm
I performed the Fourier tranform, removed the marks corresponding to the striped with the healing brush tool (I know, not exactly the most scientific method), then did an inverse Fourier transform. It was pretty easy.
Posted by: Stu Jul 27 2006, 05:08 PM
Great discussion guys, enjoying it
Bit more playing about... you know what it's like, once you start you can't stop... and this little fella is interesting.
http://img.photobucket.com/albums/v509/cumbriansky/caldera-lakeQ.jpg
Anyone else looking at that and thinking "It looks like it's in an impact crater or a caldera..."?
Posted by: volcanopele Jul 27 2006, 05:18 PM
Bit more playing about... you know what it's like, once you start you can't stop... and this little fella is interesting.
http://img.photobucket.com/albums/v509/cumbriansky/caldera-lakeQ.jpg
Anyone else looking at that and thinking "It looks like it's in an impact crater or a caldera..."?
Looks like an Ionian patera to me, not so much an impact crater.
Posted by: Stu Jul 27 2006, 05:23 PM
Ionian eh..? Yep, can see that now you point it out, thanks... Googled those and "http://www.planetaryexploration.net/jupiter/io/images/chaac_patera_cll_pia02566a.jpg" looks like a close relative indeed...
All these scattered bodies of liquid... connecting channels... drainage features.. amazing place!
Posted by: volcanopele Jul 27 2006, 05:36 PM
I was thinking more of some of the other paterae in the Camaxlti Patera region:
http://pirlwww.lpl.arizona.edu/missions/Galileo/releases/26Oct_i27c21camaxtli.html
Yaw Patera at lower right and Ruaumoko Patera west of Camaxtli Patera might be good matches.
Posted by: JRehling Jul 27 2006, 05:45 PM
http://pirlwww.lpl.arizona.edu/missions/Galileo/releases/26Oct_i27c21camaxtli.html
Yaw Patera at lower right and Ruaumoko Patera west of Camaxtli Patera might be good matches.
If it turns out we're looking at something more like Io than Minnesota, maybe the dark areas are a solid sheen of frozen water ice that is thin enough to let RADAR peek through in some places? This would be disappointing from the "methane cycle" perspective, but exciting from the volcanic perspective. Since we've already got one Io, I'm rooting for the lakes.
Posted by: tty Jul 27 2006, 06:39 PM
To me the landscape looks rather like the "loess edoma" areas of northeastern Siberia. These are areas where a mixture of fine aeolian dust and ice was deposited during the last glaciation. The result is something inbetween loess and glacier ice. The material is slowly melting and the result is a lot of shallow roundish basins, sometimes partly, sometimes completely filled by water. The whole landscape looks rather karst-like, and the phenomenon is also known as "thermokarst".
I suppose something similar might occur on Titan with ice or tholin "sand" and methane "ice".
Take a look in Google Earth along the Siberian coast from ca 140 to 175 east. One can find pretty good matches for a lot of the "lakeland" features.
tty
Posted by: Richard Trigaux Jul 27 2006, 07:07 PM
Interesting to note that these rounded shapes were not formed by the water actualy filling them, bu by the melting/thawing of a mixture of loess and ice.
Posted by: ustrax Jul 28 2006, 10:11 AM
Not a single drop of science accuracy on this:
http://i16.photobucket.com/albums/b14/ustrax3/l1-1.jpg
Posted by: mchan Jul 28 2006, 10:15 AM
Then that obviously can't be a lake since it would require a lot of drops.
Posted by: The Messenger Sep 3 2006, 11:47 PM
It is difficult to figure how tholins could be piled up into dunes large enough to be visible from Cassini. 'Sandy' structures do not transfer energy in a homogenious fashion: hard crystals develop point stresses would immediately melt tholin hydrogen bonds, forming flowing waxes, not sandy dunes. And if the material is soaked or saturated with methane, it only makes the tholin melting problem worse. Tholins saturated with methane should behave more like sugar saturated with water.
Posted by: nprev Sep 27 2006, 12:44 AM
New high-latitude lakes from T18 radar obs: http://saturn.jpl.nasa.gov/news/events/titan20060923/index.cfm
Man...IF they do indeed contain fluid, sure would like to drop a line in there & see what I might possibly catch... maybe use a can of WD-40 for bait...
Posted by: nprev Sep 27 2006, 02:06 AM
Hmm. So in your opinion, do the dunes consist of a molecularly simple compound resistant to such decomposition, perhaps water? Perhaps H2O is Titan's analog of SiO2 on Earth...
Posted by: Matt Sep 29 2006, 06:55 PM
We've seen how effective the nitrile-doped rain is at eroding the landscape, so you would not be suprised to find a lot of sand on Titan in the form of H20, but I thought the latest spectra showed the dune regions represent a depletion in H20, and are hydrocarbon rich.
It looks like the dune fields are comprised of actively saltating smog particles that blow up against the western margins of those big islands. Fluvial erosion (obviously much less active compared to aeolian transport) seems to occasionally provide the H20 sand, and I see there is some evidence for downwind transport of it in radar images.
Could abrasion from some of these wind blown hydrocarbon particles erode water-ice bedrock? I know this form of erosion occurs on Earth but I'm not sure about Titan.....
I suppose dune composition and origin is one of the big questions know, and I hope it gets answered during this mission. Is there any planned altimetry over any of the dune fields?
Posted by: The Messenger Sep 30 2006, 07:55 AM
Posted by: Sunspot Oct 12 2006, 10:46 PM
More lakes:
http://saturn.jpl.nasa.gov/multimedia/images/image-details.cfm?imageID=2325
In this image taken by the Cassini radar system, a previously unseen style of lakes is revealed. The lakes here assume complex shapes and are among the darkest seen so far on Titan.
Posted by: marsman Oct 13 2006, 12:17 AM
http://saturn.jpl.nasa.gov/multimedia/images/image-details.cfm?imageID=2325
In this image taken by the Cassini radar system, a previously unseen style of lakes is revealed. The lakes here assume complex shapes and are among the darkest seen so far on Titan.
Stunning! Reminds me of fractal patterns. Titan has an incredibly interesting landscape. With the data captured so far, I wonder if the science community can extrapolate the relative occurance of methane/ethane lakes around the northern latitudes and poles compared to the equatorial regions. I am assuming there are significant average surface temperature differences between latitudes that would be a reason for the variation.
Posted by: nprev Oct 13 2006, 04:36 AM
Stunning is definitely the word...I think this just may clinch the case for contemporary liquid presence.
In fact, what does the similarity of these landforms to terrestrial water erosional features say about both the surface properties and the fluid properties (i.e., viscosity)? Odd indeed that a place with such radical compositional and environmental differences from Earth and Mars should resemble them so much... 
Posted by: OWW Oct 13 2006, 09:03 AM
http://photojournal.jpl.nasa.gov/catalog/PIA01942
Spectacular! You can clearly see 'rivers' flowing into the lakes!!!
Posted by: ustrax Oct 13 2006, 10:18 AM
Spectacular! You can clearly see 'rivers' flowing into the lakes!!!
Approaching http://i16.photobucket.com/albums/b14/ustrax3/Titanobserver_a15.jpg...
Posted by: ustrax Oct 13 2006, 01:31 PM
From http://photojournal.jpl.nasa.gov/catalog/PIA01942
http://i16.photobucket.com/albums/b14/ustrax3/Titanobserver_a16.jpg
http://i16.photobucket.com/albums/b14/ustrax3/Titanobserver_a17.jpg
Posted by: Matt Oct 13 2006, 09:32 PM
Nice work!
Posted by: MarcF Oct 14 2006, 10:53 AM
I'm really impatient to see a mosaic of the T16-T18-T19 swaths to have a better view about the global (or lets say the regional) organization of the "Lake district". Are the lakes more numerous (or bigger, or deeper), closer to the north pole ? I may imagine a small north polar sea, which current evaporation leaves behind hundreds of isolated ponds at its border.
Marc.
Posted by: Julius Oct 14 2006, 11:36 AM
I fully agree with;there's a great possiblity for such a sea.The new lakes we see thou seem to dismiss the idea that lakes have to be somehow linked to volcanic calderas . The new shapes suggest otherwise.
Posted by: power Oct 14 2006, 01:27 PM
hi,
has this article http://www.newscientistspace.com/channel/solar-system/dn10304-slushy-volcanoes-might-support-life-on-titan-.html in New Scientist about titan volcanoes something to do with the discussion posted here in july?
Posted by: centsworth_II Oct 14 2006, 02:51 PM
Wow! This look at Titan's "Great Lakes" is amazing! I hope that in a few years time, hopefully after a rainy season, another look shows big changes. Or perhaps the lakes are now at their fullest and in years will shrink?
Posted by: ustrax Oct 16 2006, 03:05 PM
Wow...Can't climb a hill?...http://i16.photobucket.com/albums/b14/ustrax3/Titanobserver_a18.jpg
Posted by: ustrax Oct 16 2006, 03:36 PM
http://i16.photobucket.com/albums/b14/ustrax3/Titanobserver_a19.jpg
Posted by: ustrax Oct 17 2006, 08:52 AM
http://i16.photobucket.com/albums/b14/ustrax3/Titanobserver_a20.jpg...
Posted by: stevew Oct 19 2006, 11:29 PM
I agree with you. The more I play with the lakes images the more I see. The radar can penetrate through many materials, for example if the liquid were pure methane it might penetrate several meters (it's probably not pure, but that's an endpoint). I see drainage patterns within several lakes, they almost have to be on the bottom. The more "grainy" textures could also be bottom, maybe in the shallowest areas......
http://img.photobucket.com/albums/v509/cumbriansky/lakes-detail.jpg
Now, before anyone tells me off for my "playing about" and points out, rightly, that you can't just take these raw images and pull info out without a LOT of work, please bear in mind I KNOW all that, okay?
I'm no Nix or Nirgal or Horton, and I'm not suggesting this means anything, I'm just curious what I might have seen. I know the features might just be imaging artefacts, but... oh, just take a look and see what you think. I'm just pushing the ball down the hill here, not making any claims. I would be interested to hear what others think tho. Sticking my neck out here, to me it looks like the "drainage channel" on the lower right hand side actually continues into the "lake" for quite a way, maybe even flowing beneath an "island" of some sort. Other things look like they're in there too, but I'm just wondering if the "lake" is actually very shallow and we can see channels on its floor...
http://img.photobucket.com/albums/v509/cumbriansky/lakes-features.jpg
...but heck, what do I know...
Posted by: JRehling Oct 20 2006, 05:02 PM
Spectacular! You can clearly see 'rivers' flowing into the lakes!!!
How about that peninsula that is somewhat lobate... That looks to me like a lava flow, although whether it seriously predates the formation of the lake basin or not is another issue. It reminds me of the "landing strip" that Huygens imaged.
Posted by: nprev Oct 20 2006, 10:00 PM
Sure would be interesting to monitor these bodies of whatever over a long period of time. Particularly interested in seeing if there are periodic changes in fluid clarity/radar properties; those lakes may well be cauldrons of chemical activitiy under the right circumstances.
Posted by: remcook Nov 8 2006, 12:11 PM
Now in press at Icarus:
Hydrocarbon lakes on Titan, by Mitri et al.
http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6WGF-4M93PFT-2&_user=126524&_handle=V-WA-A-W-CE-MsSAYZA-UUA-U-AAZCCWBYVW-AAZBAUVZVW-CAWAEZUY-CE-U&_fmt=summary&_coverDate=11%2F07%2F2006&_rdoc=4&_orig=browse&_srch=%23toc%236821%239999%23999999999%2399999!&_cdi=6821&view=c&_acct=C000010360&_version=1&_urlVersion=0&_userid=126524&md5=931253990c21988a4ed99e903120b3c4
Posted by: JonClarke Nov 12 2006, 09:16 PM
Sorry if this has been discussed before, but how transparent is liquid methane at the Cassini radar wavelengths? if these dark areas are liquid, it looks as if the radar is seeing thorugh the liquid and imaging the bottom topography.
The other question is how sensitive is the radar reflection to ground "moisture" from pore methane? in other words, do the differences in reflectivity reflect different "moisture" states?
Jon
Posted by: nprev Nov 12 2006, 11:32 PM
Actually, the problem seems more complex than just CH4's characteristics. My impresssion is that the fluid in these lakes may be a very eclectic mix of simple (and maybe not-so-simple) organics. It's even possible that different lakes may have significant differences in composition depending on local surface "water tables" and runoff contributions.
Bottom line here is that broad-spectrum studies should be undertaken within Cassini's equipment limitations. That way we could at least rule some things out. I doubt that we'll ever be able to get definitive positive answers until we send an MSL-equivalent (or better) mission designed for Titanian conditions to perform in situ analysis on a sample or ten.
Posted by: centsworth_II Nov 13 2006, 03:59 PM
From Emily's Oct. 12 Planetary Society Blog entry:
http://www.planetary.org/blog/article/00000733
Steve Wall -- Implications for Methane Cycle
"... we may be seeing through the liquid and sensing the lake bottom.
These lakes are likely methane of unknown purity, and the penetration
characteristics of the radar depends greatly upon purity."
Posted by: JonClarke Nov 14 2006, 10:54 AM
http://www.planetary.org/blog/article/00000733
Steve Wall -- Implications for Methane Cycle
"... we may be seeing through the liquid and sensing the lake bottom.
These lakes are likely methane of unknown purity, and the penetration
characteristics of the radar depends greatly upon purity."
Thanks for that. I remembered seeing something like this but could not remember where.
Jon
Posted by: nprev Nov 16 2006, 02:54 AM
New pop-level "summary" article on Cassini's Titan findings so far:
http://skytonight.com/news/home/4653966.html
One interesting tidbit is that no mountains have yet been found that are higher than 1000 meters. I've been assuming that H20 on Titan plays much the same role that SiO2 does on Earth, so does this perhaps imply that Titan's crust doesn't have anything like the tensile strength of our own? Doesn't seem like there's a cryological-mineral-equivalent of granite, either. Maybe some constraints on crust composition can be deduced from this.
It just occurred to me why Titan may be so undeniably weird by our standards framed against the Great Pluto Debate: Titan is the only known example of a "dwarf Jovian"! The key discriminatory factor is initial composition, which is probably a function of distance from the Sun during formation.
Posted by: helvick Nov 16 2006, 12:33 PM
That's a very good point but it's size\density makes me think that a better term would be an Ice Dwarf than a Dwarf Jovian.
Posted by: ngunn Nov 16 2006, 12:54 PM
Also we have evidence that at least some of the highest parts of Xanadu consist of very low density (possibly porous) material, so they could even be floating isostatically. Impact crater rims would provide a more secure constraint on crustal strength, but I don't know if we have heights for these yet.
Off topic, but in case any Titan fans missed it I just wanted to flag up on a Titan thread that there's interesting OPAG stuff about Titan in the OPAG thread (which is currently in Jupiter orbit).
Posted by: Myran Nov 17 2006, 06:39 PM
Yes bring a lot of Titans together and it wouldnt quite end up with something like Jupiter or Saturn. Titan have lost the hydrogen it mighthave had at the time of formation.
Yet the end result would have a core not completely unlike the big iceplanets Uranus and Neptune.
So I agree.
Posted by: tty Nov 17 2006, 07:30 PM
Mountains, and indeed continents, float isostatically here on Earth too, so this in itself does not tell us anything about the relief or strength of the surface.
tty
Posted by: Julius Nov 20 2006, 01:42 PM
Latest flyby should have determined the composition of the dunes.Any news yet!?
Posted by: volcanopele Nov 20 2006, 06:48 PM
No news yet. considering how long it has taken VIMS to get any composition data out of Titan, I wouldn't hold your breath. Or at least don't hold your breath for a single answer to be released.
Posted by: JRehling Nov 20 2006, 07:49 PM
Moreover, consider what a blunt instrument (speaking figuratively, of course; I'm sure VIMS is quite pointy in parts) IR spectroscopy is. After TES had mapped Mars, we ended up knowing that there were two kinds of dark rock, and one type of dust, without much more known with certainty. (Earth analogues were suggested, but not conclusively. Of course, landers had analyzed the dust, but that wasn't thanks to TES.) After NIMS had imaged the icy Galileans, we came away knowing that there was a nonicy component in the crusts of Ganymede and Callisto and a nonicy component of Europa's crust which could be narrowed down to a short list of candidates.
Titan's unlikely to be a simpler case than those.
Powered by Invision Power Board (http://www.invisionboard.com)
© Invision Power Services (http://www.invisionpower.com)