Titan's Equatorial Sand Seas |
Titan's Equatorial Sand Seas |
May 7 2007, 03:53 PM
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#1
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Senior Member Group: Moderator Posts: 2785 Joined: 10-November 06 From: Pasadena, CA Member No.: 1345 |
I’ve put together a sequence of events that could explain the morphology of the Equatorial Sand Seas. (An example basin similar to Shangri-La is shown)
This could explain the ria-like topography [http://en.wikipedia.org/wiki/Ria] on the Eastern shore, as well as the VIMS dark blue western parts of the Sand seas, and the placement of the dark brown unit on the Eastern parts of the sand seas. 1. Basin formation. 2. Water-ice sand deposition [slowly, suddenly?] forms an ice-sand margin 3. Mobile dark brown dune sands deposit on E side, depositing inland up W facing valleys. :attachment] The dark brown sands will blow in following the predominantly W winds and make a dust coating on low-lying terrains on the eastern margins. This will be visible by VIMS and ISS as the dark-bright margin, placed “inland” from the "real margin" and will accentuate the local topography as seen by optical instruments. This accentuation on the E margin will make the Equatorial Sand Sea visible margin look “swoopy” and windblown (in effect, it is) from the dark basin. Similarly, the W margin will have a dark blue zone that appears blown from the western bright areas. On the Eastern shore, the RADAR images will place the smooth-dark/mottled gray boundary far to the W of the VIMS brown dark-bright margin. (RADAR should be able to penetrate a thin coating of dark sands). The features in the limbo zone have been covered by dark sands, perhaps not enough to form dune structures, but enough to cover up the ice-sand margin, the near shore terrain, and perhaps even some of the underlying bright terrain. This makes the deposition sequence in the Equatorial Sand Seas: 1: Basin formation 2. Major water ice sand emplacement 3. Dune sands cover up low-lying downwind valleys (enough to mask visible imagery) Other Equatorial Sand Sea basins should look very similar around Titan: Shangri-La, Belet, Senkyo, Fensal and Quivra. Local winds may play a bonus role, but the overall trend of dark sand deposition up valley should be towards the E. For example: the false-color image in Figure 6 of the Soderblom paper seems to imply a predominant wind vector in Fensal and Quivra to the ESE. [I’m pretty sure all this has been described in pieces before, but it gave me a really great excuse to play with PowerPoint. ] -Mike -------------------- Some higher resolution images available at my photostream: http://www.flickr.com/photos/31678681@N07/
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Jun 14 2007, 07:23 PM
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#2
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Senior Member Group: Moderator Posts: 2785 Joined: 10-November 06 From: Pasadena, CA Member No.: 1345 |
Here is a short list of possible suspects for the “bright center dark halo circular features”:
(Listed in order of “drama”: high energy impact is high drama (and would be way rad to watch happen!), a slow cold diapir slowly working it’s way to the suface is low drama (and not real exciting to watch). External: Impact origin followed by modification (impact then maybe cryovolcanism or slow crustal rebound?): 1) Modified impact crater (up-lifted dome) 2) Modified palimpsest/type II palimpsest/penepalimpsest 3) Modified central dome crater Internal: Cryovolcanic origin 4) Collapsed pancake dome 5) Thermal plume 6) Ice pluton 7) Diapir The difficult thing to explain is the formation of a topographically depressed halo around the central dome or plateau. Any ideas? -Mike -------------------- Some higher resolution images available at my photostream: http://www.flickr.com/photos/31678681@N07/
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Jun 15 2007, 09:28 AM
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#3
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Senior Member Group: Members Posts: 3516 Joined: 4-November 05 From: North Wales Member No.: 542 |
The difficult thing to explain is the formation of a topographically depressed halo around the central dome or plateau. I have to say that I feel uncomfortably out on a speculative limb here. In particular I think your assumption that elevation and liquid levels are the only determinants of the light/dark patterns is unsafe. However, going along with it for now I don't find it too hard to imagine the outer skin of an ice diapir being richer in volatile materials, making it more prone to deflation by outgassing and/or erosion. One could envisage a dark depression appearing first, acquiring a bright centre later as more of it emerges. |
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Jun 15 2007, 06:24 PM
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#4
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Senior Member Group: Moderator Posts: 2785 Joined: 10-November 06 From: Pasadena, CA Member No.: 1345 |
I have to say that I feel uncomfortably out on a speculative limb here. In particular I think your assumption that elevation and liquid levels are the only determinants of the light/dark patterns is unsafe. I'm totally cool with your concerns. All of these speculations are built up on the original speculations of a bright/dark level being pretty much set by "the last inundation sea level". (= "house of cards"?) (There may be some effect of dark brown dune sands drifting in from the W as well). It is also built up on the speculation that most of the sand sea basins (exception: Mezzoramia) are interconnected and have a "last inundation sea level" at the same gravitational level of the geoid. (The semi-permanent tidal bulge will make a difference in absolute elevation). A key observation that supports this hypothesis is that at the Huygens site (granted, only one local observation), the bright dark boundary appeared to be very close to the "seashore" of the islands. Hopefully this hypothesis would be easily testable from an altimetry track across one or several Sand Sea Basins. If the above hypothesis is correct, we should observe the bright/dark boundary at the same (tidal bulge effects taken into account) absolute elevation across all the basins. Alternate hypotheses for setting the light/dark boundary include: * local "bright stuff" snow line: (if bright stuff is solid material) * local methane rain virga limit (assuming bright stuff has been scrubbed clean by methane percolation) * local "fog elevation" (assuming methane fog helped dissolve out bright material) (If y'all got any others?) Like any other supposition, if data comes in that torpedoes these assumptions, it'll be time to modify the hypothetical sequence. But so far, everything seems kinda consistent.... So far.... -Mike -------------------- Some higher resolution images available at my photostream: http://www.flickr.com/photos/31678681@N07/
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