[X] My Assistant

[peter59]

T7 swath released !
PDS - Cassini Radar

Volcanopele ! Time for update your site.
Titan RADAR SAR Swaths

[volcanopele]

It should be updated on Monday.

[alan]

Small version for the impatient

[dvandorn]

Thanks, Alan, for all of us impatient types!

I'm seeing several circular features in this swath -- if I didn't know any better (and I don't), I'd say they look like subdued impact features which have been mostly eroded into nothingness. Perhaps overlaid by sedimentary deposits. But I see lots of what really look, to me, like old craters. (Especially near the top of the lower third of the swath, above the obvious large flow feature that trends from bottom to top.)

This is one of the first times I'd say we see what looks like typical cratered terrain anywhere in the Titan radar swaths... even if it's been eroded to near-flatness.

-the other Doug

[alan]

Speaking of alluvial deposits, is that what we are seeing in this section of the T7 SAR?

[Phil Stooke]

The speckly nature of SAR images can make them difficult to interpret. Here I have suppressed it. Maybe this is a bit easier to look at. Well, maybe... but is it an area of alluvial deposits? The patterns of streaks might suggest it, but I don't see anything conclusive. More context would help, seeing for instance if a channel feeds into it or if it occurs at the foot of a range of hills.

Phil

[alan]

Phil, I linked to a smaller version of the entire swath in this thread.
http://www.unmannedspaceflight.com/index.p...=2745&st=29

[hendric]

Or it could be a bunch of dust-devil trails.

[Phil Stooke]

Thanks, alan. I had missed that. Well, the context does look promising. Two long channels cutting through a mottled area, opening into a smooth flat area. Could be alluvial. This really makes you want a good DEM, though! The next mission just has to give us global SAR and topography...

Phil

[elakdawalla]

It should be updated on Monday.

And it was! Thanks, Jason
http://pirlwww.lpl.arizona.edu/~perry/RADAR/

[volcanopele]

I have added the T7 swath to my RADAR swath page:

http://pirlwww.lpl.arizona.edu/~perry/RADAR/

Unlike Alan, I used the BIFQI version of the file. From the looks of it, the pixel values range from 0.05 to 1.4 or so, so I am guessing in this product, the pixel values have been converted to dielectric constant or some RADAR equivalent to I/F, like I do with ISS images while the BIBQI version uses the actual brightness values. the "F" version may also be corrected for incidence angle (or emission angle or what ever...). I would ask our resident RADAR team member, but I'm not sure he is in town.

I should also point out that the file has been rotated 90 degrees CCW from what is in the PDS. Also, if anyone wants lat-lon gridded versions at 128 pixels/deg., let me know.

EDIT: If I looked in the label file, I would find my answer... "The data values in this file are Synthetic Aperture Radar (SAR) normalized backscatter cross-section values. The values are physical scale (not in dB) and have been corrected for incidence-angle effects. The raw backscatter values have been multiplied by the function f(I), where I is the incidence angle and f(I) = 1.4142*sin(I)."

[The Messenger]

I went to drain the kiddie pool yesterday, and discovered a bunch of that silicate stuff they pack into diapers had leaked into the pool. I realized the density of this sandy jell is slightly greater than that of the water, which may correlate somewhat with the density of surface materials on Titan, relative to the atmosphere.

I played around a bit, swirling or setting up waves in the pool, then watching how the 'dust' settled. It is easy to create swirling patterns, and roundish blotches, a little more difficult to set up wave patterns (like Titan's dunes) - the flow has to alternate directionally at nearly 180deg angles, and any swirly motion quickly disrupts them.

I could only get alluvial patterns by setting up patterns in the underlying plastic. Before the dust settled, the alluvial patterns are dark, afterwards, light. I know this may sound silly, but it could explain why some of the alluvial patterns on Titan seem to be light and others dark - it could be a function of age, emissivity, and whether or not the 'sand' that seems to dominate the cat scratch regions is able to percolate into the alluvial gorges...and who was in the pool

[Guest_AlexBlackwell_*]

I just noticed Emily's interpretation of some of the geology we're seeing. Interesting.

[Guest_Myran_*]

For dvandorn and others looking for craters. There's one bona-fide crater in the right end of this radar image.

[The Messenger]

I just noticed Emily's interpretation of some of the geology we're seeing. Interesting.

Some of the terrain Emily finds difficult to interpret may resemble "The Fins', in Arches National monument. This was a sandstone sea bed that was pushed up and out from beneath. The fins cracked and spread, then were cross-cut by a river, with some dune formation on the edges. On the whole the terrain was incomprehensible, at first.

[The Messenger]

Frazier has posted this ESA picture of the iani depression on Mars:

http://www.universetoday.com/2006/07/17/iani-chaos-on-mars/

Which may be similar to the chaotic part of T7. I am also reminded of some of the hills and terrain around Fairbanks, where permafrost is melting and potholes and fissures are opening up chaotic gaps.

[Olvegg]

Considering recent discoveries of countless Northern Lakes, what can be said about the 'liquidity' of this southern 'sea'? Is Mezzoramia dark enough to be a sea today?

[tasp]

Is it too early to ponder how these Titanian fluids 'work' the surface ??

We see incised flow features in many locations. Does the fluid flow directly erode into the surface, or do entrained minerals or grains aid the 'cutting' process ?

On earth water is a polar solvent, IIRC, most of the candidate fluids for Titan are non-polar, do those fluids 'do' erosion the same way ?

[Juramike]

Is it too early to ponder how these Titanian fluids 'work' the surface ??

We see incised flow features in many locations. Does the fluid flow directly erode into the surface, or do entrained minerals or grains aid the 'cutting' process ?

On earth water is a polar solvent, IIRC, most of the candidate fluids for Titan are non-polar, do those fluids 'do' erosion the same way ?

A hydrocarbon solvent should behave sorta-kinda similar to water erosion on Earth:

1) Any "chunks" or pieces of material carried along the stream and bouncing along as sediment grains will physically abrade the streambed. The chunks could be loose pieces of ice sand, insoluble salts, or insoluble organics. (Just like the muds, sands, boulders and rocks in a meltwater stream during flood stage).

2) Hydrocarbon solvent may leach out (dissolve) emplaced organics on the surface. (The organics having been emplaced during geological processes forming the surface. For example: water circulating around through pores after an impact or cryovolcanic event could emplace veins of partially soluble organics. Just like an ore vein on Earth). In this case the ground liquid could chemically dissolve the veins and cut into surrounding hard ice-rock.

3) [I'm speculating here] Additionally, methane may transition to vapor at Titan's surface temperature. So an initial rainfall hitting hot rock, or a flash flood cruising down a gully, could cause an initial methane boil-off. The boiling would start at small cracks and surface defects of the streambed. I imagine that the expansion of the methane bubbles during boiling would physically help expand the cracks and defects to break down the streambed. (Just like freeze-crack-thaw on Earth - except we are dealing with a surface close to the boiling point of the cycling liquid, rather than the freezing point. And since methane contracts when it freezes, it would lack the molecular "oomph" of water's freeze expansion. It is thus at methane's boiling point where things get interesting.)

The important thing to remember is that water ice is pretty much insoluble in pure hydrocarbon solvent. (Additives could help however). Just like how most rock is pretty much insoluble in pure water.

A lot of details can be found in Lorenz and Lunine Icarus 122 79-91 (1996) "Erosion on Titan" .

-Mike

[elakdawalla]

No, it's not too early to ponder that. Here's a couple recent papers from Geoff Collins on the topic. If you email him he'd probably send you full versions of the articles, he's a nice guy.
Relative rates of fluvial bedrock incision on Titan and Earth (GRL, 2005)
Incision of Fluvial Channels on Titan (AGU abstract, 2005)

And by Devon Burr (Geoff is a coauthor, along with Ralph Lorenz)
Sediment transport by liquid surficial flow: Application to Titan (Icarus, 2006)
(Note it's a new thing that ADS has Elsevier journals in its database...hooray!)

Those should keep you busy

--Emily