[X] My Assistant

[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.



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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

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[Juramike]

Ganymede et.al.
Undoubtedly we can look to the Galileans and other moons of Saturn for guides to Titan's likely bulk composition. Also, large impacts might be expected to produce comparable surface features. However I think it's worth reviewing the actual and potential differences. In the first place neither the ISS albedo patterns nor the topography revealed by radar on Titan remotely resemble any other body. Secondly it is reasonable to expect that the the geology of Titan will reflect the fact that volatiles brought to the surface are not immediately vented into space.

The geology of most the Saturnian moons should be very, very similar. Geologically, they are all brothers and brought up in the same house (Saturn orbit). The big differences with Titan compared to the other Saturn moons are with regard to impactors are:

it has weather and floods (erosion will erase many of the features)
it's bigger: tectonic activity? cryovolanic activity? (might erase many of the features)

it's bigger (compositional makeup, depth of lithosphere)
it has an atmosphere (small impactors burn up, a big impactor should not be affected, but venting might be suppressed [very good point, ngunn])
it has organics on the surface (but this might not be enough to make a difference)
it's bigger: faster impactor speed???

The first two factors could help explain why there are so few obvious impact craters (they get wiped), and may explain their different form compared to other moons.

IIRC (but I can't remember the source), the impact features of Saturnian moons (other than Titan) seem to resemble the impact features of terrestrial planets more than those of Galilean satellites. The Galilean satellites seem to be sorta "oddball" (compositional differences of target material? lithosphere differences? impactor differences?).

So we would predict that without erosion, Titan craters should look like other Saturn moon craters/terrestrial craters with a possible trend to Galilean craters. (The trend being due viscous relaxation of icy surfaces on larger bodies).

Ganymede et.al.
On Earth the recycling of water lubricates plate tectonics. We have no idea what analogous processes may operate on Titan. Thus we don't know even if ancient circles would remain circular - or even remain at all. More data required!

I don't think ancient circles remain circular at all....(I think some of this data might already exist)...

-Mike