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.


Click to view attachmentClick to view attachmentClick to view attachmentClick to view attachmentClick to view attachment[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

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.

Click to view attachmentClick to view attachmentClick to view attachmentClick to view attachmentClick to view attachment[attachment=1037
: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

Just in case you're wondering Mike I'm following your posts here with interest. It bothers me that if the prevailing winds are all one way there is still so much dune material out in the open that hasn't made it all the way to western side of a high obstacle by now. Either the wind reverses sometimes or the dune material is occasionally carried right over the 'continents' (without sticking) by exceptional gales. Also, what happens to a dune in a deluge? Shouldn't there be some dunes visibly damaged by flooding? Have we seen that anywhere? Does flooding somehow 'wipe the slate' from dark brown back to dark blue? Too many questions!!! I think we might answer some of them by following the Huygens flood deposits both upstream to their source and downstream to the first appearance of dune material, preferably with all of SAR, ISS and VIMS.

I think a massive rain storm around the equator might be useful in that respect to shake things up a bit. I'm thinking equinox here Let's hope all is still working and funded by then (only 2.5 more years!)

Those are excellent questions.

I'm trying to find RADAR images where an obvious stream crosses over either VIMS brown dark unit material or VIMS dark blue unit material.

If flooding does 'wipe the slate' from dark brown back to dark blue, I would expect to observe large dark blue margins in some areas along the Eastern shores. (as well as Northern, Southern, and Western shores - but the W ice sand margin is most susceptible to being covered up by windblown dune sands)

But we don't see any large ice sand margins in the E.

So the dune sand movement apparently happened AFTER the last major dark blue margin flood deposition event.

-Mike

Very good questions. On earth, we definitely find 'prevailing drift' patterns to the east or west of mountains - even small hills.

Another factor to consider is the information released by NASA/Ciclops about the circulation of Saturn today. The atmosphere is flip-flopped from prior models - the 'dark bands' are thought to be drawn up from the deeper layers, while the 'light bands' are thought to originate in the upper atomosphere. This has application to Titan, if it is assumed the Dark bands of Saturn have the same or similar composition to the dark surface features of Titan. Is atmospheric chemistry on Titan a major or minor contributor to the color patterns we see on the surface?

Yep, that's just about right!

There are a few examples of both RADAR dark and RADAR bright channels lying on top of (presumably) VIMS dark blue deposits in the Equatorial Sand Seas.

These are shown here (channels indicated by yellow arrows):
Click to view attachmentClick to view attachmentClick to view attachmentClick to view attachment


I was not able to find any examples of a dune field clearly cut through by a channel (either bright or dark). The area near western Xanadu in the T13 RADAR swath shows a large delta complex that feeds into the Shangri-La. A “channel” may be barely visible, but it does not cut through a dune area located to the W. The dark smooth area may be where a broad outflow fan of ice sands was deposited, then overlain by dune seas. This is shown below (delta indicated inside yellow box, potential channel/outflow fan with green arrow):
Click to view attachment


So it appears that RADAR-dark channels and RADAR-bright channels overlay dark blue ice sands, but not dark brown dune sands.

So deposition sequence (first to last):

1) Dark blue ice sands
2) Channels (RADAR-bright/RADAR-dark)
3) Dark brown dune sands

This also implies that the dark blue ice sands are not always infinitely permeable to liquid. They can support a stream, at least in some locations. This is very similar to wet terrestrial sand. Perhaps the dark blue ice sands are almost saturated with liquid, or perhaps they have a slight barrier to the liquid (semi-permeable crust). Perhaps in most locations, a small decent-sized flow can soak in, but a massive flood event will scour across the surface for a distance. In some areas, permeability is locally reduced, and even normal amounts of flow will course across the surface.

Since a massive feeder network of channels and ponds is not observed, rain must be able to soak into the sands to some extent. (Impermeable dirt would quickly create an eroded out network.)

At the Huygens landing area, there are large and small channels visible in the straights off the island. There are also streams that flow off the island into the dark area. But I could not discern a connecting channel between the channels in the straight, and the outflow of the streams coming off the island. The outflow from the island streams seems absorbed by the dark blue ice sands. Perhaps the channels were carved during major flood events, presumably from the flow coming down the straight (SW to NE) and not from the island streams.

From the available data so far, RADAR-bright channels streaking across the ice-sands are not common. This implies that the equatorial sand seas are relatively flat. Irregular rough (RADAR bright) boulders cannot be supported by gradual slopes. The fact that we do observe channels does imply a slight change in elevation, so the Sand Seas are not totally flat. Further analysis should be able to determine flow direction (thus topography).

-Mike

Nice work, Mike. However I would propose an alternative caption to your 1 2 3 list as follows:

"Titan surface features in decreasing order of formation timescale:"

My reasoning is that the active processes involved are probably all concurrent over the long term. All that's needed to produce the apparent sequence is for the massive outwash floods to be very infrequent compared with 'ordinary' channel-forming rains and dune movement. I'm not even sure about the dunes coming third. Have you found any dunes that have drifted across (and blocked) a channel?

Ah, perfect: that the key phrase I was trying to come up with. Thanks!

All these process are occuring either simultaneously or episodicaly. From any given point, I'm asking "What is the last event that happened here to make it look this way?"

For example: a particular area may have had decades of stream deposition with dunes covering them at the same time, but then a massive flood came along and erased evidence of both of these events.


As for dunes covering over channels, I have not yet found any that clearly cut across a dark channel. (Anyone else seen one?)

-Mike

Here are some images and locations where dunes have partially buried a channel:
Click to view attachmentClick to view attachmentClick to view attachment


In the RADAR images of some of the dark channels in an earlier post (#8, above), dunes can be seen at the terminus of the channel.

I was not able to find any images where a channel was blocked by dunes, and then the channel was clearly modified by the blocking dune.

It appears that dune deposition is the "more-often happening event". The dunes are mobile. Or at least more mobile than the channels.

-Mike

Here is an example of a smaller isolated Dune Sea. This is a smaller area to the W of Minerva Crater in an area North of Xanadu. It is bounded to the W by a bright area (continent? highland?) that presumably should block any sands from entering the basin.

Click to view attachment

Since there is a sand sea present, either:

A. Sand can go over the bright areas.
B. Sand can be washed in from bright areas.
C. Sand occasionally comes from other directions, but the prevailing flow is generally W. (In this case the basin would be a sand trap)


There are several (flat?) RADAR-darker areas in Xanadu that do not have cat-scratch dune fields. This implies that either the RADAR-bright material covers or modifies the sands, or that the sands are not able to flow over large continental masses.

Gee, I wonder what is the nature of the bright material?

-Mike

Thanks for all the awesomeness, Juramike

Wish I had as much time to spend on analysing the Cassini data as you do!
Between Cassini observation planning and the Titan flagship study (presentation
to OPAG should go up on the OPAG website in due course), I'm barely
managing to read all the posts.....

I think in the bright area to the East of Menrva on T3 (with all the anabranching
channels) you will see a couple of faint dark streaks on the bright oval, suggesting
these are dunes that are superposed on a fluvial basin...

Mike, in your first illustration in post 11 (for example) I'm not quite sure what sequence of events is evidenced. Where your upper yellow arrows are pointing the dune pattern, including whatever constitutes the inter-dune surface, certainly continues uninterrupted. However it's not clear that the dark channel was continuous at this point until being buried by the dunes. Where the lower arrows are pointing is very interesting though. I can persuade myself that I am seeing a very narrow channel that has been 'recut' through the ends of the dunes. It would be interesting to look for more like that. (I'm sure you will!)

[quote name='rlorenz' date='May 12 2007, 04:40 PM' post='90040']
Titan flagship study (presentation
to OPAG should go up on the OPAG website in due course)

A b&w printout thereof is already on my coffee table. It's a lot easier to read than the Europa one if, like me, one isn't well versed in the latest management and planning jargon.

quote:
I'm barely
managing to read all the posts.....

Thanks again for contributing here.

I stumbled a publication (PDF) entitled: 'Comparative Sediment Transport By Flowing Liquid on Earth, Mars and Titan: Synthesis Of Theory And Observations'

It could be of some interest, although you probably already know about it.

However, it's the first time I have seen it....

I stumbled upon a publication, rather.

^link?

Bill

http://www.lpi.usra.edu/meetings/lpsc2007/pdf/2222.pdf

I'm new to all this linking stuff...let's see if I got it right....

I’ve put together a hypothetical sequence that could explain the RADAR and VIMS appearance of the craters observed in the Equatorial Sand Seas. (Craters such as Sinlap, the T17 swath crater in W Fensal, and Guabonito). This sequence also explains the puzzling appearance of the bright material which highlights the crater rims and central peaks.

Click to view attachmentClick to view attachmentClick to view attachmentClick to view attachment
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1. Crater forms, either before or after the Sand Sea basin forms or is partially filled in..
2. Water ice sand erodes on outside of crater, forming a debris apron or ice sand margin.
3. Bright material is deposited.
4. Liquid or fog percolates up to a set topographic level at the crater. All bright material below this line (“highest sea level”) is dissolved/modified/washed away.
5. The liquid (fog) level retreats, leaving crater high and dry and revealing previous units.
6. Mobile dark brown dune sands deposited on W side, but don’t fill in downwind (E) in the wind shadow of the crater.


Here are some examples of what we would expect to observe from this scenario, compared to actual VIMS and RADAR images:

Click to view attachmentClick to view attachmentClick to view attachment


This nicely explains the bright material deposited on the rim of the crater, but not on the blue ice sand margins (in some of the craters like Sinlap). It also explains the bright deposit on the central peaks of Sinlap, as well as on the central peak of the crater-shaped feature NE of the Huygens Landing Site (seen in ISS)..

The key to this sequence is that the bright material was deposited BEFORE the last major sea level rise.

It is possible that each item in the sequence is periodic, rather than a one time deal. So the deposition of bright material is episodic and rare, floods are less rare, and dune sands move quite often.

The bright/dark line around the Equatorial Dune Seas are fixed by the last major sea level height attained in that basin after bright material was deposited.

Craters that formed environments that were eventually deeply flooded will have a significant light blue and dark blue sand ice margin that extends outside the brightest material deposit (especially to the W). They will have a bulls-eye pattern in VIMS. Those craters that formed in areas that were only slightly covered in liquid at it’s highest point will have a very small blue ice sand margin that extends beyond the bright material – these will have a very asymmetric look in VIMS (strong trailing to the E). Some craters were never inundated and thus would only have bright material covering the entire crater complex – these may not show up by VIMS, only by RADAR.

Craters that formed in what was eventually a deep liquid environments include Sinlap, the Western T17 RADAR swath crater in Fensal, and Guabonito.
Craters that fomed in an enviroment that was eventually shallowly covered in liquid include Minerva, and the crater(?) that is on the W tip of Quivra (seen in the T25 RADAR swath)
Craters that formed in environments that were never inundated include the crater on the N end of Shikoku Faculae. (not obvious in ISS, but seen in RADAR).

By this analogy, Fensal is deeper than Aztlan. And Shangri-La nearest Xanadu is deep (subduction?) and Shangri La is very shallow near it’s contact with Adiri.

In general, areas with steep shorelines (“highest level attained after the last bright stuff deposition event”) will have fewer indentations and have a smoother light/dark border (i.e. Xanadu). Areas with shallow shores with relative highest topography closest to highest sea level height will have very jagged and irregular bright/dark borders (ancient bright stuff/liquid shorelines). From this we would predict that average elevation of Adiri is very close to the highest attained level. It may be an area that has been gently upwarped to a level just slightly above the highest attained sea level in Shangri-La basin after the last bright stuff deposition event.

The bright island at the Huygens Landing Site sits just above the level of the “highest level of liquid attained in Shangri-La after the last bright stuff deposition event”. The bright/dark contact line of the highland sits at the highest level of liquid attained in the Shangri-La basin. In the channel some of the sand bars have bright material deposited on them. This should allow us to link the two units. The bright stuff on the sand bars would also be just poking above the highest level of liquid attained in the Shangri-La basin after the last bright stuff deposition event..

The analogy of the Great Basin of North America, painted white, and then flooded with a Glacial Lake Bonneville amount of turpentine and then drained seems pretty close. (Possibly very close chemically).

-Mike

This seems like as good a place as any to deposit this experiment, rather than resurrecting the old map thread. This is a largely cosmetic retooling of the Fensal-Aztlan portion of the global map with the currently released SAR swaths overlain (T3. T13, T16, T17, T25). The resolution here is barely decent enough to make out the dunes in places, but it gives a pretty good indication of what sort of mapping products will be possible from these growing datasets.

Click to view attachment

Wow! Thank you, Exploitcorporations!

(Looks like I muffed the image of the VIMS inset of the T17 W Fensal crater. I thought it was the crater at the north nortwest end of your image (it just got missed by the T17 swath, although the southern debris apron might've gotten picked up). I should have grabbed the image of the crater much further to the W. It's interesting how those two craters look fairly similar with a slight "wing" off the NW part of the crater.)

I would predict that when this "bulls-eye crater" is imaged by RADAR SAR, that it will look very similar to the T17 W Fensal crater, and to Sinlap crater (but possibly with an even bigger apron).

-Mike

simply...wow! amazing how sharp it is!

What crater? Are you talking about the feature that you thought was Ksa?

(I think when the boss-man finds out, I'm doomed! )

But thank in advance for all your suggestions, input , and helpful guidance when you are able!




The perfect "smoking gun" SAR RADAR image would have a N or S flowing channel which is either cut by or cuts into the E-->W flowing dune features. I haven't found this yet. [Odd, I'm kinda suspecting that most tectonic features seem to trend E-W in the equatorial zone].


Based on Dr. Lorenz's suggestion, I found an interesting are to the SW of Minerva that consists of a bright stream (pretty much originating at the outer wall of the crater) that feeds into a delta complex that is being encroached upon by dunes. (Or is the delta encroaching the dune field? based on the sharpness of the dunes lines at the E edge, I think it is the dunes encroaching upon the delta). These dunes have a funky look. Further to the SW it appears to be a channel with dunes lying across a RADAR-dark channel.

Here is the annotated image:Click to view attachment


Is the RADAR-dark channel continuous (in this location or the other locations)? I really can't say, but I would strongly speculate that the dunes are lying on top of a continuous dark channel.

-Mike


P.S. "Anabranch" is my new word for the day!

The RADAR image in my post is of Ksa (I got that one right).

The ISS image (which I thought was Ksa, but it is not) is of the feature at center top mentioned in the second image of your previous post.

I've indicated some of these features in a section clipped from the wonderful mosaic posted today (thanks, again!) by Exploitcorporations:

Click to view attachment


In Figure 6 of the Soderblom et al paper "Corellations between Cassini VIMS spectra and RADAR SAR images: Implications fo Titan's surface composition and the character of the Huygens probe landing site", this feature in the VIMS processing to make Figure 6 has a very small blue ring around it. (I'd also argue that his larger buddy to the E also looks similar). I suspect that this is a very low-lying crater (old?) that when eventually imaged by RADAR will look like a miniature version of Minerva. (Mini-Minerva?).

To the SW is an interesting feature that also has a blue tail in VIMS, but seems relatively dim by ISS. Could this be another type of feature (cryovolcano?) or a very low-lying crater that did not get a large dusting of bright material or suffered only partial scrubbing?

Can't wait for more RADAR!

-Mike

hmm, I suspect that the feature you thought was Ksa is actually a Ganesa-type cryovolcano, with a flow to the east and north...

Are there easy ways to discern between a cryovolcano and an impact feature?

-Mike

Well, it would be nice if it erupted. That would make it much easier

To be honest, it would require a good ISS/VIMS observation of Ganesa to determine what a Ganesa-type feature looks like in VIMS and ISS images. My basis for saying, at the very least, to hold off on declaring that feature a crater, is that while it is circular, there are a number of other ways to form circular features, like the Ganesa-type pancake dome. The apparent flow to the east and north and the fact that it doesn't match the appearance of other dark terrain craters (Guabonito, Sinlap, Velas, and the guy north of Adiri), with very dark interiors, intermediate albedo crater walls, and bright raised rims/ejecta blankets also suggest that we should serious consider a cryovolcanic origin for this feature. But, I'll admit the evidence is about as conclusive as Tortola Facula (the VIMS snail from Ta) being a cryovolcano.

Hmmm. Actually, there might be a way to see a recently erupted cryovolcano, at least in the dark basins:


If the hypothetical scenario presented above (post#21) is correct, anything that recently coughed up bright material (ammonium sulfate + other salts?) AFTER the last bright-material-dissolving event should be pretty obvious by VIMS and RADAR.

In that case, we would expect a ISS and VIMS stain in the dark basin that would be larger than the RADAR signature. (Older features that had their bases scrubbed should have a smaller ISS and VIMS stain compared to RADAR.)


Similarly, any impacts (or bulges that did not release bright salt material) in the dark brown basins after the last bright-material-dissolving event should be dark brown. They should not have any VIMS or ISS bright material on them compared to their surrounding area. Are there any craters visible only by RADAR that appear dark brown by VIMS?

-Mike

Here's another work in progress. This makeover of the Adiri-Shangri-La regional view is cobbled together from the ISS basemap (10/06), the obligatory SAR swaths (T8/T13), raw frames from the 13 May T30 encounter, the nifty CICLOPS "looking ahead" Celestia mosaics, and a cannibalized 1/64th of Paul McCartney's birthday present. This is presented in the standard Exploitcorporations LLMF Equal-Area Projection ™, so plan on losing your blimp anywhere west of the center of the map.



Click to view attachment

Very nice. I hope you will do more of these.

Phil

Exploitcorporations

All your work is breathtaking. Agree with Phil Stooke. Please continue!!!!! Just Wonderful!!!!!

Craig

Wow!! That is totally awesome!!!

I just rearranged my office posters to make room for these!!

Thank you for all your efforts to make these images!!

-Mike

One of the dark channels from the T8 RADAR swath in western Belet (or eastern Senkyo) has a very curious appearance: at both ends of the of the 3 km channel there are RADAR dark smooth areas that is over 25 km2 in size. This symmetrical “bone shaped” appearance may have resulted from a tidal current flushing back and forth through the channel.

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For comparision, I have compared the zoomed RADAR image of the Dark Channel in W Belet with a graphic showing marine topography of Deception Pass in Washington State (Deception Pass Coordinates: 48 degrees 24’ 23”N; 122 degrees 58’40” W). Deception Pass is located near the San Juan and Gulf Islands in Washington/British Columbia. This island group was formed through crustal extension and inundation to form an archipelago (sound familiar?). The entire the island group (especially the Gulf Islands of British Columbia) appear morphologically similar to areas on Titan. Deception Pass is notable for having an extremely strong current due to tidal effects. (A Seattle Times article on Deception Pass can be found here.)


The way Deception Pass (and by analogy, the W Belet Dark Channel) develops ferocious tides is shown in the graphic below:

Click to view attachmentClick to view attachment

1. Tidal bulge reaches from the Pacific Ocean into the Strait of Juan de Fuca.
2. Sea level on the west side of the Pass rises faster than the sea level on the eastern (Skagit Bay) side of the Pass.
3. Height difference of 4.5 feet between the two sides causes eastward flow of 56,000 m3/s water through the channel
(for comparison, the Mississippi River average flow is 17,600 m3/s).
4. As the sea levels on either side of the Pass eventually equilibrate, from both water flowing into Skagit Bay from through the Pass, and the longer route around Whidbey Island, the flow through the channel drops to near zero.
5. Tide bulge leaves Pacific
6. Sea level on west side of Pass drops faster than Skagit Bay can empty out.
7. New height differenential sets up, now current flows west (Skagit BayPacific) through Pass (Ebb tide –cycling to Lo).
8. Skagit bay sea level drops, sea level differential drops to zero, flow through channel drops to near zero.

In the Google Earth image you can actually tell which way the current is flowing when the Google Earth image was taken (Hint: Flood tide into Skagit Bay).

The deeper areas at the two entrances to the Pass are swept clean from the current. (The Skagit River dumps a huge amount of sediment into the bay, if the current did not sweep the sediment out to sea, all the topography on the Skagit bay side would become a mudflat, similar to the area at the extreme NE of the Deception Pass graphic). There are other tidal channels in the San Juan Islands that display almost the same pattern of bottom topography: a narrow channel with localized depressions (deeper areas) at both tide channel exits. (Examples include: San Juan Channel; Spieden Channel; Harney Channel; Upright Channel; and Thatcher Pass.)


The Dark Channel in western Belet (or eastern Senkyo) is approximately 3 km wide. This is 6x wider than Deception Pass.

Using the formula [Flow (m3/sec) = 0.46 X1.61 channel width (m) ^1.22] that was used for other channels on Titan, we arrive at a predicted flow of 13,000 m3/s for the W Belet Dark Channel..
Extrapolating from Deception Pass numbers (Pass width = 500 m), we instead arrive at an extrapolated flow of 336,000 m3/s for the W Belet Dark Channel.

Either way, it’s pretty impressive. Given the relative size of the dark areas at the ends of the channel (>25 km2!), I would be inclined to favor the larger numbers.

If this is a tidal channel on Titan, it tells us several very important things.

1. There was a large sea or ocean in this area.
2. The sea or ocean lasted long enough to experience several tide cycles (with a 14 day cycle?)
3. Large flow rates were set up through the tidal channel.
4. The basin on the W is approximately at the same level as the basin on the E (at least the high methane mark)

(An alternate possibility to be considered is that the channel is bi-directional and resulted from a single/multiple flood events going from E to W, then later from W to E.)

If the deposition sequence put forward in post #21 is correct, we would expect that this channel should appear dark by ISS. I would expect that during the time the channel was inundated, tidal currents would have swept the Dark Channel clear of loose sediments. So this area may be relatively clear of ice sands and windblown dune sands compared to other areas in the Equatorial Dune Seas. If the channel bottom can be resolved by VIMS, the channel itself may be very interesting – it may give us a glimpse into the bottom substrate that exists under the dune seas. I’m hoping this area gets observed during the upcoming May 31 pass.

I wonder if other tidal channels can be found by further examination of RADAR or VIMS images of Titan’s surface?
Could we use these to infer the tidal pattern and current flows of past methane seas on Titan? (Astropaleohydrology?)

-Mike

Surely Titan's Saturn synchronous orbit would inhibit tides ?

I woulda thought so, too.

But Tokano et al. invoke Titan's orbital eccentricity around Saturn as causing tidal winds on Titan. (Tokano, T; Neubauer, F. M. Icarus, 2002, 158 499-515. "Tidal winds on Titan caused by Saturn." Abstract available here)

Their paper is discussing tidal winds in the atmosphere, but their arguments (and diagrams) would also seem to extend to large bodies of fluids on Titan's surface.

-Mike

I remember reading a paper before Cassini reached Saturn that claimed Titan couldn't have oceans and continents because the tides would produce enough erosion to eventuallly wear down the continents until they were below sea level.

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

You're probably referring to one of the two following papers:

The tide in the seas of Titan
Carl Sagan and Stanley F. Dermott
Nature 300, 731-733 (1982).
Abstract

Tidal effects of disconnected hydrocarbon seas on Titan
Stanley F. Dermott and Carl Sagan
Nature 374, 238-240 (1995).
Abstract

We have a beautiful example of a tidal channel here in North Wales - the Menai Strait:
http://biology.bangor.ac.uk/research/wetla...es/image032.jpg

Tidal range is up to 10m at one end and about half as much at the other. The phase difference is about one hour beween the two ends. Currents reach 8 knots. there are several deep spots including one near the NE end.

Menai Strait chart attached:
Click to view attachment

Note that this is quite a young feature - it has probably widened and deepened considerably even since Roman times. I guess the same could be true for the Titan feature, so you might only need a (relatively) brief wet episode to produce it.

(I sooooo totally could not resist this...)


Further support for the similarity between Titan's archipeligos and the San Juan Islands of the Pacific Northwest:
"gunkholing!".

-Mike

If we are saying that the equatorial basins once contained liquid then presumably tides could have caused much larger scale erosion features than just that small winding channel in Western Belet. In fact it could have been a major factor shaping the morphology of the basins, particularly their margins. Is this what you have in mind, Juramike? That could mean that quite a lot of the streaky features that we have been thinking about in terms of dunes and prevailing wind patterns are really tidal erosion features merely exploited and rendered more visible (like a fingerprint) by a 'dusting' of dune material. Some of the funny directions might make more sense that way. I have never been entirely happy about the wind patterns on Titan being redirected in major ways by what is really quite modest topography, but liquid would be another matter.

Yup. That's what I'm thinking:

1. Basic morphology of the archipeligoes set up from impacts and crustal extensions (maybe even plate subductions?)
2. Grabens and basins partially filled up with eroded sands.
3. Bright stuff deposited from cryovolcanic venting.
4. Inundation with methane (removes lower parts of bright stuff, and sets up tidal channels which accentuates topography of grabens ("dancing monkey" of T28?).
5. Dune sands blowing around with the prevailing W wind.


There may have been several cycles of inundation/tidal erosion and bright stuff deposition.

If we see an obvious tidal channel (from RADAR) that is VIMS bright, we could argue that the particular tide channel was set in place in an earlier inundation/ocean event that occured BEFORE the last bright stuff deposition. (i.e. massive big huge inundation/tidal erosion-->bright stuff deposition-->big inundation leaves the lower bathtub ring).

I have not seen any obvious signs of earlier pre-latest-bright-stuff shorelines or benches (except maybe the "Ghost Coast" area in NW Xanadu in the T13 RADAR swath).

-Mike

Are the sand basins really very far below the surrounding light-colored regions? If they were liquid-filled, how deep would they be?

Those are really, really good questions!

How deep from "highest sea level since bright stuff deposition" to lowest sediment level in the basin?
(How much liquid did the basins hold at the last flood event?)

And also how deep is the dune/ice sand layer to the basin substrate?
(How much sediment has washed in?)


The only papers I have found with altimetry data tracks over Equatorial Sand Sea basins are:

Soderblom et al Planetary and Space Science, 2007, article in press. (Topography of Huygens landing site areas)
Sotin et al. Nature, 2005, 435, 786-789. (Topography of line offshore S of "Snail" feature in Shangri-La)
Elachi et al. Science, 2005, 308, 970-974. (Topography of line in NE Fensal? (or did it just miss the basin?))
Rodriguez et al LPS (2007) Abstract (and figure) freely available here. (I think this is the same track as in Elachi paper - NE Fensal?)

Does anyone know if there have been any other altimeter or topograhic data released of an Equatorial Sand Sea basin?

-Mike

Another question, Mike. I'm looking at the 'sliced carrot'/'Mcnaught tail' feature to the north of Adiri. To me that looks like a wide ridge (possibly a very large ancient crater rim) eroded through in several places by tidal currents. The northeastern margin of Belet shows a lot of lineation trending roughly the same way which could also have arisen from somewhat more random original topography modified by tidal action. Does that fit with your picture?

Excellant theory, Mike. If the sand dunes are still active - not frozen, we should see patterns change; and if the dunes are moving, the channels are likely being replowed, at least seasonally, by active tides. This is the best explanation I have seen for both the oddball flow patterns suggested by the 'channel', the connected 'lakes'; and the competing dune and gorge terrain.