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T44 Flyby (May 28, 2008), The Last Flyby of the Primary Mission
titanicrivers
post Aug 9 2008, 02:07 PM
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'So is that dark object in the PIA10956 a dome or a lake with a crusty zone?'

That radar dark area reminds me of a degraded crater (or dried up lake) with a delta wash through deposit. There appears to be a channel (black arrows) flowing from (do I dare say) from East to West (white arrow). Can't quite make out the outlet breach for the shizzle but I wonder if it eventually joins the larger delta to the west.

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Olvegg
post Aug 9 2008, 04:38 PM
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It must be located somewhere between and slightly north of Eir Macula and Tui Regio:
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Juramike
post Aug 9 2008, 05:02 PM
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I think there's some seriously complicated stuff going on in this image:

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I suspect that there is a long channel (tectonic fault? ancient riverbed?) running from NW to SE (red arrows in image; red dotted line in diagram).
This may have been an old river channel.

This runs parallel to the bright dark boundary and seems to run parallel to some of the mountain chains (and also to the RADAR seam - so the line up of the mountain chain could be a look angle effect).

The violent bend (indicated by blue arrow in image) in the western wide RADAR-bright channel (channel A, dark blue in the diagram) happens right where it intersects this long channel. Could it be that it captured part of the ancient stream channel?

Going upstream a tad from the first 90 degree bend, the channel turns away from the long NW to SE channel and cuts through the mountains. It appears that it's direction is altered due to a roughly W-E tectonic ridge (black dashed line in figure) that breaks the NW-SE channel.

It is VERY interesting how the Stream channel A cuts straight line through the NW-SE mountains. ("Like butter").
To me, that implies that either the stream existed first, and the mountains rose up slowly as the stream cut through (example: New River in the Appalachians) or that the river was cutting a straight course in a sl. sloping soft landscape and erosion slowly revealed the mountain range as the covering landscape eroded away (example: Green River through the Uinta Mountians).

On the other side of the EW tectonic ridge, near the circular feature there is a RADAR-brighter wispy feature ("B", light blue, I'm not comfortable calling it a channel near the circular feature) that runs roughly parallel to the tectonic ridge until it turns into the NW-SE long channel.

The current drainage pattern seems to be constrained by the EW tectonic ridges, but use (capture) segments of the (older?) NW-SE long channel.

-Mike





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Juramike
post Aug 9 2008, 05:45 PM
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This "dome or crusty lake thing" is really bugging me. There appears to be a RADAR darker outer margin as well.

It is a RADAR dark circular feature with a RADAR-brighter margin facing the look angle, as well as an outer RADAR-dark outer margin in the direction of the look angle.
This would be consistent with a RADAR dark feature with a semicircular trench/channel/valley at the edge.

The dark outer margin of the Xanadu feature is puzzling: the Ganesa Macula dome doesn't look like this, the lakes (even the crusty ones) don't look like this. The RADAR-bright margin of these Ganesa and the crusty zone lakes blends into the background.

The only thing I've seen similar is another dark circle in the NW Xanadu tectonic ridge image (PIA10654). It also has the same aspect with regard to look angle. (It is also situated next to an EW tectonic ridge as well).

Here is an graphic showing these two features in comparison. (I'm no longer real comfortable calling the NW Xanadu feature a degraded crater.)

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-Mike


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stevesliva
post Aug 9 2008, 07:07 PM
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The analogue I keep thinking of is water flowing on top of a glacier, creating total chaos:


And the channels starting out from both on top of and beneath the glacier forming channels on the plain...


So what are the chances that you get the solid phase being eroded by the liquid phase of the same compound in those radar bright areas? With ice/water on earth on polythermal glaciers, you also get the occasional supraglacial lake:


I guess it's required to have temperatures both above and below the freezing point at various times in the year...
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Juramike
post Aug 9 2008, 09:39 PM
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QUOTE (stevesliva @ Aug 9 2008, 03:07 PM) *
I guess it's required to have temperatures both above and below the freezing point at various times in the year...


Not necessarily. (Those are really pretty pictures, BTW)

You could have some sort of organic solid being extruded out onto the Titanian surface. It could be plastic enough when it comes out to make a pancake shape when it hits a flat surface (like pancake batter). But some of the materials may be easily dissolved, or could be liquid themselves. (Hypothetical example, a mixture of acetonitrile and ethane bubblin' up from the ground, as the acetonitrile sets up, the ethane separates out and flows away, like liquid water in the glacier examples above.)

That would leave you with a dome of an organic solid (acetonitrile in the example above) with flow features around the margins.

Altough the dome shape might be similar, the mechanism would be different from a cryovolcanic pancake dome like Ganesa Macula. Ganesa is presumably cryolava (molten ice + organics). The "chemical glacier" described above is more like a mud volcano or seep of a different material than the crustal stuff and at lower temperature. It is interesting that the two examples in Xanadu both seem to be up against a mountainous area (tectonic ridge) on their backsides.

-Mike


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volcanopele
post Aug 9 2008, 09:45 PM
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The Ganesa-like feature you point out Mike looks like a modified crater to me. There is a hint of a shadow along the margin that would suggest that it is a depression. The bright edge could just be rougher terrain along the edge of the depression (larger rocks washed down from the surrounding mountains perhaps).


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Juramike
post Aug 9 2008, 09:54 PM
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QUOTE (volcanopele @ Aug 9 2008, 05:45 PM) *
The Ganesa-like feature you point out Mike looks like a modified crater to me. There is a hint of a shadow along the margin that would suggest that it is a depression. The bright edge could just be rougher terrain along the edge of the depression (larger rocks washed down from the surrounding mountains perhaps).


I'll buy that.

The dark outer margin is the depression inside the rim. The RADAR-bright inner margin is rockfall from the rim, and the overall dark stuff in the center is the typical fine mud deposits.

That explanation also kinda hints as to why the surrounding streams are so bright - Xanadu rocks like to break into big RADAR-bright chunks.

(But I'm still at a loss for why the backside of these features aren't also RADAR bright. I woulda thought rockfall around the rim would be pretty uniform.)

-Mike


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Juramike
post Dec 22 2008, 02:58 AM
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QUOTE (titanicrivers @ May 30 2008, 06:08 AM) *
Raw images are up! An interesting one is shown below (1). Looks like a cloud band in N00111091 taken on May 28, 2008 from approximately 43,517 kilometers away using the CL1 and CB3 filters. Not sure of the location, probably in the southern hemisphere...

1) [attachment=14479:N00111091T44cloud.jpg]


Yup! There are four frames in the flyby set with clouds. Three of them make a sharp line at -19 S.
(That particular frame N0011091 is the one I can't figure out, but I think it's somewhere on Xanadu very close to Hotei Arcus.)

Three of the frames connect nicely across the "Pinecone" feature of Hotei Arcus, and the clouds overlap on the images.

So if we are seeing equatorial clouds, does this mean rain is coming soon?

(And are these methane clouds, or something upwind volatiles up?)


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ngunn
post Dec 22 2008, 12:00 PM
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Nice. I've just checked the diagram with all the observed cloud locations on P14 of the recent Turtle, Perry et. al. lakes and weather paper. It does seem that -19 is one of the favoured latitudes, though rather less so than the others at -70, -40 and +56.

EDIT - The 'nice' image is of course in the Xanadu thread here http://www.unmannedspaceflight.com/index.p...st&id=16801
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Juramike
post Dec 22 2008, 06:49 PM
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I think the T44 images are part of the data that was presented in the figure of the Turtle, Perry et al paper.

I'm pretty sure they correspond to the red rectangles (2008 data) in the figure. Which means that the fourth image NO111091 should be on a line with and to the W of the westmost image in the mosaic.

Which...I...just...couldn't...make....fit...

[I'll need to use the T47 Xanadu mosaic to make a T46 mosaic; then use the T46 mosaic to line up the last T44 image. The T46 set seems a little more accessible, is nice and high-res, and doesn't have as much apparent vignetting.]

One thing I noticed, is that even after lining up the surface features between two images, the clouds themselves seemed to move between images. There was a slight shift from one frame to the next. This might be a parallax effect, or it could be from me not being able to line up the images well. I think the clouds might be waaay the heck up there.

Might be fun with someone with more math skills to try to estimate cloud height based on the slight shift due to spacecraft motion. (Unfortunately, only one cloud frame was obtained over "The Pinecone", that would have made image lineup and distance estimation easier).

-Mike


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titanicrivers
post Dec 22 2008, 10:28 PM
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I'm pretty sure they correspond to the red rectangles (2008 data) in the figure. Which means that the fourth image NO111091 should be on a line with and to the W of the westmost image in the mosaic.

Which...I...just...couldn't...make....fit...

Mike. The photos were taken at different distances from Titan by NAC. According to the raw images N0111091 was taken by the NAC about 2hrs before closest approach (at 43,517 km out). The frame of the NAC from mission description (and presumably any photos taken ) would cover latitudes 25-30 deg South, a bit different from the latitude of your cloud band. (see post # 16 and # 18). Photos N00111076 to N00111079 were taken a bit farther out from 57,911 to 54,583 km so a slightly different latitude may have been centered in the NAC. Also about 30 minutes would have elapsed between N00111079 and N0111091 and some cloud movement and configuration change may have occurred.
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peter59
post Apr 8 2009, 06:19 AM
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T44 - Equatorial Anti-Saturnian hemisphere (Southern/Southwestern Xanadu, Eir Macula, Eastern Tui Regio, North-central Shangri-la, Southern Dilmun)
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Juramike
post May 12 2010, 10:01 PM
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T44 SAR Swath released as PIA12989


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