Titan's Equatorial Sand Seas |
Titan's Equatorial Sand Seas |
May 7 2007, 03:53 PM
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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, 02:49 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 |
Approximately 60% (30 out of 50) of the “circular/oval features” in the EXCEL table from post 85 (above) can be described as “bright center dark halo circular features”.
Here are a few examples by ISS, RADAR and RADAR/ISS imaging: From the supposed deposition sequence and topology above, the ISS brightness is assumed to be terrain that was above the high methane mark during the last big inundation (after bright stuff was deposited). The RADAR brightness is assumed to be due to rough terrain. So: ISS bright, RADAR bright center = rough terrain left high and dry during last inundation. ISS dark, RADAR dark = smooth low lying terrain where bright stuff was dissolved/modified/washed away during the last inundation. (Either low lying dune sands (VIMS dark brown) or ice sands (VIMS dark blue)). Most likely, the bright center dark halo circular features have a rough central plateau or dome surrounded by a smooth depression. Taking Coats Facula as an example, here are images showing hypothetical makeup that could explain the observed morphology: (Coats Facula’s opening is downwind, thus dune sands were not able to penetrate into the dark halo. VIMS imaging of Coats Facula shows that the halo consists of dark blue ice sands. Other halo depressions where dune sands can easily penetrate should appear dark brown by VIMS). The proposed deposition sequence is the same as in post 21 (in this thread), except instead of the word “crater” substitute the awkward phrase “bright center dark halo circular feature”. -Mike -------------------- Some higher resolution images available at my photostream: http://www.flickr.com/photos/31678681@N07/
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