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Titan's topography, strange....
Juramike
post Apr 12 2009, 12:44 PM
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Recent article in Science by Zebker et al.:

Zebker et al. Science in press, "Size and Shape of Saturn's Moon Titan". doi: 10.1126/science.1168905
(published online April 2, 2009)

Link to abstract (pay-for article): http://www.sciencemag.org/cgi/content/abstract/1168905

Article on spaceref discusses this paper: http://www.spaceref.com/news/viewpr.html?pid=27912

Figure 3 from the Science article is a global elevation map relative to barycenter.

Key points of article:
  • Poles are squished - might explain why lakes are up there
  • "Mountains" aren't necessarily elevated - they might've sunk down into the crust to form "a basin of their own creation".
  • (quote from spaceref. article)
  • Large scale features do not appear correlated with elevation
  • Xanadu and Tseghi are BASINS! (ca. -600 m to barycenter)
  • Adiri is higher than Xanadu (by almost 1 km)
  • Dilmun is also pretty elevated (+ 400 m relative to barycenter)
  • highest elevated terrain on Titan seems to be region around "Adiri junior" in the S Senkyo "basin" at ca. + 600 m above barycenter
  • Shangri-La "basin" is elevated +400-800 m ABOVE Xanadu (using barycenter elevations in Fig. 3)



"Xanadu seems to be systematically lower than other parts of the equatorial belt, and not uplifted like most mountainous areas on Earth." (quote from Fig. 3 caption in article)

-Mike




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Some higher resolution images available at my photostream: http://www.flickr.com/photos/31678681@N07/
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ngunn
post Apr 20 2009, 11:07 AM
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This thread has gone very quiet! In the meantime I have been trying to put some thoughts into words, and I hope I may be allowed the indulgence of a longer than usual post, even if some of it repeats what's already been said. Here goes:

- - -

Ever since we found out that the low latitude dark markings on Titan consist of drifting sands the map of Titan has been giving me a dull headache. It takes sand movement to form and maintain dunes and that means we cannot be looking at a static system. A steady state dynamic system is also ruled out by the presence of a single complete gap in the pattern. Xanadu acts in effect like a giant capacitor blocking the DC flow of sand. The next possibility is AC sand flow - an oscillating system. However, the asymmetries that we see in the sand seas must have taken ages to form, implying a very long time period for the oscillations. There is no obvious driver for such a process. It seems hard to avoid the conclusion that we are looking at a pattern that is somehow being maintained in a non-equilibrium state, hence the headache.

Now for the first time that I am aware of we have, in albedo-driven winds (and wind-driven albedos), a process proposed which would involve positive feedback. Positive feedback is exactly what's required to maintain a system in a non-equilibrium state. Positive feedback can give even a feeble or inefficient process the leverage to transform worlds, creating emergent order that makes no sense in other terms. That's why I find this idea so exciting. It raises a host of new questions and the pleasant anticipation that some of them may soon be answered.

There is a nice symmetry of scales to this explanation too. Sand dunes and the regular patterns they form are themselves emergent non-equilibrium structures maintained by a different positive feedback system involving wind and another partner, in that case local-scale topography.

We are still a long way from knowing that we have the final answer, but that does not worry me at all. I think that at least we can see clearly now what kind of answer we are seeking: a positive feedback mechanism of some sort which can render Titan's sand seas self-confining and its 'continents' self-cleaning. We have in view at last a domain of possible explanations that does not defy reason. The headache is cured.

What about the asymmetry of the sand seas and its strong implication of DC sand flow? No problem. We can have eastward drift and positive feedback operating together. This would likely produce a sand flow regime that is continuous at some longitudes and episodic at others where some underlying property of the substrate - very plausibly albedo - dams the flow. The large scale pattern of the sand seas may indeed migrate eastward over long time scales, with Xanadu simply happening to be the most effective dam operating in the particular configuration that prevails in our epoch.

- - -

I hope Ralph will pay us another visit here and share more of his insights, but even if he doesn't I don't think we've heard the last of this by a long way.
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Posts in this topic
- Juramike   Titan's topography   Apr 12 2009, 12:44 PM
- - Juramike   Here's a cartooon showing how Xanadu could hav...   Apr 12 2009, 03:32 PM
- - Juramike   The Science article is in reference to the Barycen...   Apr 12 2009, 03:46 PM
- - Juramike   So now a Big Question: Why are the poles wet, the ...   Apr 12 2009, 04:00 PM
- - ngunn   Thanks for starting off a discussion on this. One ...   Apr 12 2009, 08:24 PM
|- - rlorenz   QUOTE (ngunn @ Apr 12 2009, 04:24 PM) Tha...   Apr 15 2009, 03:39 AM
- - Doc   Forgive my ignorance ngunn but exactly what was th...   Apr 12 2009, 08:44 PM
|- - rlorenz   QUOTE (Doc @ Apr 12 2009, 04:44 PM) Forgi...   Apr 15 2009, 03:31 AM
- - ngunn   It came from RADAR reflectance observations of the...   Apr 12 2009, 09:03 PM
- - Juramike   Nigel's right, the most recent evidence comes ...   Apr 13 2009, 01:45 AM
- - Juramike   The channel drainage pattern in W Xanadu in the T1...   Apr 13 2009, 02:07 AM
- - ngunn   On the ellipsoid vs. equipotential I'm happy t...   Apr 15 2009, 09:34 AM
- - Juramike   Looking at channels in the RADAR Swaths, I haven...   Apr 15 2009, 02:34 PM
|- - ngunn   QUOTE (Juramike @ Apr 15 2009, 03:34 PM) ...   Apr 15 2009, 03:06 PM
- - Juramike   QUOTE (rlorenz @ Apr 14 2009, 10:39 PM) T...   Apr 15 2009, 03:18 PM
- - ngunn   Correct me if I'm wrong (again), but aren...   Apr 15 2009, 03:44 PM
- - Juramike   If I understand this correctly, the dunes line up ...   Apr 15 2009, 05:10 PM
- - Juramike   Two different wind regimes, but with one component...   Apr 15 2009, 05:32 PM
- - ngunn   Mike I'm having trouble reconciling what you d...   Apr 15 2009, 06:06 PM
- - Juramike   The maps show the linear dune orientation. The li...   Apr 15 2009, 07:17 PM
|- - ngunn   QUOTE (Juramike @ Apr 15 2009, 08:17 PM) ...   Apr 15 2009, 07:36 PM
- - Juramike   If I remember correctly, the GCM wind field change...   Apr 15 2009, 09:40 PM
- - ngunn   I'm just reading the transcript of the Titan s...   Apr 15 2009, 09:59 PM
- - Juramike   From looking at RADAR images, it looks like the W ...   Apr 16 2009, 02:45 AM
|- - ngunn   QUOTE (Juramike @ Apr 16 2009, 03:45 AM) ...   Apr 16 2009, 08:50 AM
- - Juramike   Bingo! Tokano, T. Icarus 194 (2008) 243-262. ...   Apr 16 2009, 02:46 AM
- - ngunn   A further thought on albedo-controlled winds. Sinc...   Apr 16 2009, 10:01 AM
- - ngunn   Let's take this even further into the realm of...   Apr 16 2009, 10:32 AM
- - Juramike   It also means that Xanadu, and processes that oper...   Apr 16 2009, 11:31 AM
- - ngunn   Possibly, but it also restores - or rather preserv...   Apr 16 2009, 11:38 AM
|- - Juramike   QUOTE (ngunn @ Apr 16 2009, 06:38 AM) Pos...   Apr 16 2009, 07:47 PM
||- - ngunn   QUOTE (Juramike @ Apr 16 2009, 08:47 PM) ...   Apr 16 2009, 09:52 PM
|- - Jason W Barnes   QUOTE (ngunn @ Apr 16 2009, 04:38 AM) Pos...   Apr 21 2009, 12:50 AM
|- - Jason W Barnes   QUOTE (Jason W Barnes @ Apr 20 2009, 05:5...   Apr 21 2009, 12:51 AM
- - ngunn   This thread has gone very quiet! In the meanti...   Apr 20 2009, 11:07 AM
- - ngunn   A poem: - - - The Walrus and the Carpenter Were w...   Apr 20 2009, 02:10 PM
- - Phil Stooke   What's an order of magnitude among friends? P...   Apr 21 2009, 02:44 AM
- - Juramike   If Xanadu is "self-clearing" then the du...   Apr 21 2009, 03:06 AM
|- - ngunn   QUOTE (Juramike @ Apr 21 2009, 04:06 AM) ...   Apr 21 2009, 08:06 AM
- - ngunn   I've just peformed an experiment which crudely...   Apr 21 2009, 03:36 PM
|- - helvick   Very nice work there ngunn - I was struggling to f...   Apr 21 2009, 04:39 PM
|- - Jason W Barnes   QUOTE (ngunn @ Apr 21 2009, 08:36 AM) I...   Apr 22 2009, 07:45 PM
|- - stevesliva   QUOTE (Jason W Barnes @ Apr 22 2009, 03:4...   Apr 22 2009, 08:43 PM
||- - Jason W Barnes   QUOTE (stevesliva @ Apr 22 2009, 01:43 PM...   Apr 24 2009, 12:39 AM
||- - stevesliva   QUOTE (Jason W Barnes @ Apr 23 2009, 08:3...   Apr 24 2009, 02:27 PM
|- - ngunn   QUOTE (Jason W Barnes @ Apr 22 2009, 08:4...   Apr 22 2009, 09:37 PM
- - ngunn   Glad you liked it. Did you listen to the Takemitsu...   Apr 21 2009, 09:54 PM
- - ngunn   After sleeping on it I'll now try to be more e...   Apr 23 2009, 08:01 AM
- - DFortes   "No disrespect," to quote Jon Stewart, b...   Apr 24 2009, 03:53 PM
- - Juramike   Link for Dorset, Acta Crystallographica B51 (1995)...   Apr 24 2009, 06:40 PM
- - Juramike   Stiles et al. Icarus (2009) ASAP. "Determini...   Apr 24 2009, 07:41 PM
- - ngunn   A stray thought on the dust-into-sand coagulation ...   Apr 24 2009, 08:25 PM
- - DFortes   On the crystalline versus amorphous debate There ...   Apr 24 2009, 10:50 PM
|- - Juramike   Good points. F.M Flasar and R.K Achterberg, Phil....   Apr 24 2009, 11:55 PM
|- - Jason W Barnes   QUOTE (Juramike @ Apr 24 2009, 04:55 PM) ...   Apr 27 2009, 06:41 PM
|- - stevesliva   QUOTE (Jason W Barnes @ Apr 27 2009, 02:4...   Apr 27 2009, 09:39 PM
- - ngunn   The paper is in the current issue of 'Science...   May 15 2009, 08:58 AM
- - titanicrivers   Wow such an incredible discussion ! It is tim...   Sep 26 2009, 09:33 AM
- - ngunn   Brilliant, TR! I think that needs doing for a...   Sep 26 2009, 09:44 AM
|- - titanicrivers   QUOTE (ngunn @ Sep 26 2009, 04:44 AM) Bri...   Sep 27 2009, 03:38 AM
- - titanicrivers   Here's a modified SARTopo map for Adiri and th...   Sep 30 2009, 11:34 PM
- - titanicrivers   Here's a modified SARTopo map of the Huygens l...   Sep 30 2009, 11:41 PM
|- - titanicrivers   QUOTE (titanicrivers @ Sep 30 2009, 06:41...   Oct 4 2009, 05:17 PM
- - Juramike   The "spooky dude" feature still puzzles ...   Oct 4 2009, 06:00 PM
- - ngunn   Mike, I noticed that you had implied this in one o...   Oct 4 2009, 07:15 PM
- - titanicrivers   I would also wonder if catastrophic flow was runni...   Oct 4 2009, 07:58 PM
- - ngunn   Against that suggestion I would note that these ov...   Oct 4 2009, 08:31 PM
|- - titanicrivers   QUOTE (ngunn @ Oct 4 2009, 03:31 PM) Agai...   Oct 6 2009, 08:20 PM
- - Juramike   Elevation shows the spooky dude formation is eleva...   Oct 5 2009, 12:14 AM
|- - titanicrivers   QUOTE (Juramike @ Oct 4 2009, 07:14 PM) E...   Oct 5 2009, 01:49 AM
|- - ngunn   QUOTE (Juramike @ Oct 5 2009, 01:14 AM) E...   Oct 5 2009, 06:12 AM
- - ngunn   Interesting comparisons there for sure. I'd li...   Oct 6 2009, 09:03 PM
- - Juramike   This oval feature shown above is part of the ...   Oct 7 2009, 12:34 AM
- - Juramike   Graphic showing elevation trace (based only on th...   Oct 7 2009, 01:11 AM
- - ngunn   Right! Got my position wrong, but the argument...   Oct 7 2009, 07:28 AM
|- - titanicrivers   QUOTE (ngunn @ Oct 7 2009, 02:28 AM) Righ...   Oct 11 2009, 10:35 PM
- - ngunn   That's great: I so much prefer a sequence of s...   Oct 11 2009, 11:10 PM
- - Decepticon   titanicrivers WOW!   Oct 12 2009, 12:43 AM
- - Juramike   Nice overlay TR! I'm not sure if the Spoo...   Oct 12 2009, 02:35 AM
- - titanicrivers   The recent http://photojournal.jpl.nasa.gov/target...   Aug 25 2010, 02:02 AM
- - Juramike   Interesting how the channels go to the north into ...   Aug 25 2010, 02:28 AM
|- - titanicrivers   QUOTE (Juramike @ Aug 24 2010, 08:28 PM) ...   Aug 25 2010, 07:08 AM
- - Bill Harris   TR-- Nifty topography. Reminds me of an uplifted...   Aug 25 2010, 04:17 PM
- - Decepticon   ^ I tried to do the cross eyed thing and my result...   Aug 26 2010, 02:21 AM
- - titanicrivers   I found this article via Wikipedia that may help y...   Aug 26 2010, 08:51 AM
- - titanicrivers   Here is another 2D to 3D image that is relatively ...   Sep 1 2010, 05:43 AM
- - titanicrivers   N00153307-9 composite with 2D to 3D conversion and...   Sep 7 2010, 06:27 AM
- - titanicrivers   N Aaru Mountains, Titan. T16 SAR swath Part2, edi...   Sep 10 2010, 08:31 AM
- - titanicrivers   Things are a little slow with Titan at the moment...   Dec 6 2010, 06:56 PM
|- - algorimancer   QUOTE (titanicrivers @ Dec 6 2010, 12:56 ...   Dec 7 2010, 01:59 PM
- - titanicrivers   Agree the horizontal ridge is not compatible with ...   Dec 11 2010, 07:46 AM
- - AndyG   My head's not wired to do cross-eyed 3d images...   Dec 11 2010, 09:09 AM
- - Juramike   Yeah, my head's not wired for side by side vie...   Dec 11 2010, 02:37 PM
- - titanicrivers   Here's a favorite spot on Titan for many of us...   Feb 27 2011, 07:47 AM
|- - algorimancer   Very subtle topography in this one. Incidentally...   Feb 28 2011, 04:11 PM
- - titanicrivers   T8 SAR part 2 contains lots of interesting topogra...   May 9 2011, 05:13 AM
- - titanicrivers   The recent Photojournal image http://photojournal....   Jan 6 2013, 05:58 AM
- - Ron Hobbs   I just saw this on the JPL web site: Cassini Sugg...   Jan 8 2013, 07:33 PM
- - stevesliva   I bet there's some fantastic small-scale topog...   Jan 8 2013, 10:45 PM
- - Ron Hobbs   Yeah, my mind is quivering with possibilities. Ma...   Jan 9 2013, 04:02 AM
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