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 22 2007, 01:42 AM
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#2
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Member Group: Members Posts: 723 Joined: 13-June 04 Member No.: 82 |
If Titan had global oceans on its surface, its tides would be enormous. Saturn's gravity well is far deeper than Luna's, and the eccentricity of Titan's orbit would be sufficient to induce tides measured in hundreds of metres. I worked through the calculation in an earlier post a couple of years ago, and came up with a result of about 150m.
(the tides are not caused by rotation within the tidally influencing body's gravity well, but by the local gravity differential across the diameter of Titan varying in strength due to the eccentricity of Titan's orbit) Since there is no global surface ocean on Titan, the tides would be proportionately smaller. I have to imagine that even such relatively small seas as we do see must have a tidal range of several metres, depending on the differential distance to Saturn between the closest and farthest points of the sea surface. At a first estimate, each 100km difference in distance to Saturn between the closest-to-Saturn and farthest-from-Saturn points of a single sea on Titan should produce about 3m of tidal range at those extremities. This tide would take the form of a 'slosh' with a period of roughly 15 days, with the sea levels on the sub-Saturn hemisphere reaching a maximum at the point closest to Saturn, and minimum at the point farthest from Saturn, when Titan is closest to Saturn, and the opposite pattern -- the sea levels at a minimum at the point closest to Saturn, and maximum at the point farthest from Saturn -- when Titan is farthest from Saturn. The shoreline midway between these two points should have little or no tidal range. Seas on the anti-Saturn hemisphere would have the opposite tidal pattern. Of course, local seabottom topography would have a big effect on tidal ranges too. Bill |
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