Titan's Equatorial Sand Seas Options

[Juramike]

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=1035
: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

Attached thumbnail(s)

 

[Juramike]

I used the published altimetry data to try and estimate the average depth of the Equatorial Sand Seas. The slides below show estimated traces adapted from released data.





DISR image interpretation gave relative topographical maps of two regions near the Huygens Landing Site. Region 1 is the island, and Region 2 is one of the potholes of the sandbar in the offshore channel (the “spooky dude” formation. It is assumed that the absolute topographic elevation of the two determined regions (Region 1 and Region 2) is the same. In both regions, the bright/dark boundary was estimated to be at ca. 30 m in the referenced figures.

[The highest points of the channel sandbar (region 2) are at 140 m above the bright/dark boundary. It is difficult to understand how a streambed deposit could have an elevation above the maximum sea level. (Unless maybe the sandbar was emplaced by an earlier and even higher inundation??) ]


Altimetry data from the Shangri-La basin immediately S of Tortola Facula showed a series of parallel E-W ridges that varied ” by several hundred meters”. Since these are not ISS-bright, they must lie below “sea level”, (below the bright/dark boundary). Thus, the elevations below sea level are estimated to be at least 0-200 m deep. [200 is minimal interpretation of “several hundred meters”]


The Ta altimetry trace just crosses extreme NE Fesal. Altimetry shows a shallow dip, indicating that Fensal is very shallow in this area.



Maximum depths observed:
Shangri-La basin (Huygens Landing site): at least 80 m deep
Shangri-La basin (S of Tortola Facula): at least 200 m deep
Extreme NE Fensal basin: 50 m deep

With this limited data, it appears that the basins (or at least it’s edges) are fairly shallow. Thus during the last inundation, the basins would have resembled shallow seas, not deep oceans.

-Mike

[JRehling]

I used the published altimetry data to try and estimate the average depth of the Equatorial Sand Seas. The slides below show estimated traces adapted from released data.

[...]
With this limited data, it appears that the basins (or at least it’s edges) are fairly shallow. Thus during the last inundation, the basins would have resembled shallow seas, not deep oceans.

-Mike

Nice work.

A companion analysis would be to say what kind of relief can be supported by H2O ice at these temperatures / acceleration due to gravity. Ganymede makes a very handy reference. DEMs from G1/G2 and from Voyager/G8 show delta-elevations of about 1500 m.

Take that empirical result with a grain of salt or two -- the uplift could be different in the two cases, and Titan may not be in steady state. And moreover, the stereo coverage of Ganymede is extremely limited. Also, the sand seas should be able to make steep icy slopes more "buoyant" than when they are exposed to the vacuum of space. That could preserve some deeper gorges that are under "sea level".

We shouldn't be surprised, though, if we find out that most of Titan's surface (including the icy surface submerged under sand seas) is within a range of 1500 meters or so of elevation. Since the sand seas occupy only a small fraction of the distribution [at the bottom, obviously], one would naively expect a depth that is a comparable fraction of the range. Eg, 1/10th of the range is about the bottom 150 meters. That happens to nail Juramike's estimates working from another direction.

Given the sharp linear features around Aztlan in particular, perhaps there are some isolated "Marianas Trench" locales where the sand seas are particularly deep, but that wouldn't operate across their full breadth, for sure.