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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May 8 2007, 11:44 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 |
I’ve put together another hypothetical series of events that could explain the RADAR appearance of many of the “islands” seen in the Equatorial Sand Sea.
1. Hill/ridge formation, either before or after the Sand Sea basin forms or is partially filled in. 2. Water ice sand erodes off the hill, forming a debris apron or ice sand margin. 3. Mobile dark brown dune sands deposit on E side, but don’t fill in downwind (E) in the wind shadow of the island. :attachment] This could explain the bullet-shaped appearance of the islands (or ridges) and the ghost-like tails that stretch downwind, usually towards the E. Other tectonic features, like grabens, would also show similar features. The relative height of the island above the equatorial dune sand level partly determines it’s appearance. Lower islands may not suffer erosion if they are covered by dune sands, so they may have a small or non-existant debris apron.. RADAR will penetrate the obscuring dune sands deeper, so the islands will appear bigger by RADAR than by VIMS or ISS. The eastern side of the “island” will have dark blue ice sands extending to the E as a tail. This may be visible in VIMS imaging until eventually obscured by a coating of dark brown unit dunes. The islands and features in all the Equatorial Sand Sea basin should look very similar. “Islands” and ridges in Shangri-La, Belet, Senkyo, Fensal and Quivra should all share a similar appearance. Many of the island ridges may have started out as tectonic features, like parallel ridges (as observed to the W of the Huygens landing area), or hummocks poking out of the basin. As an example, I pulled a RADAR image out of the T8 swath (PIA08454) {Actually, I used the image from TPS, for some reason it was clearer on my computer} -Mike -------------------- Some higher resolution images available at my photostream: http://www.flickr.com/photos/31678681@N07/
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