T47 Mission description available here!

VIMS noodling near Huygens Landing Site
CIRS looking at nitrile and hydrocarbon concentrations near the Equatorial limb
UVIS looking at aerosol concentrations in upper atmosphere (particulate data) from 2 (two) stellar occultations

And ISS will get some nice images of Hotei Arcus, E Xanadu, and W Fensal region (looks like Sotra Facula will be in the dark).

-Mike

Here's a very rough lineup of the T47 narrow angle images over SE Xanadu superimposed on a wide angle view:
Click to view attachment

The red box image (N00124292) ID pretty solid, the other two are less clear.
The distinctive dark "caudal" shape in N00124292 looks similar to a feature central Adiri, - is it the same type of formation? (bright tectonic ridge cutting across a dark undulatory graben?)

I think N00124920 is a shot of Hotei Arcus.

[Man, figuring these out was pretty tough...]

-Mike

I agree. It looks a lot like this one from the last encounter (posted 5 November):

"Is this Hotei Arcus? It will be interesting to look for any topographic shading at the terminator. Can't wait to see the processed mosaics.
http://saturn.jpl.nasa.gov/multimedia/imag...ID=173100"

Mind you, nobody supplied the confirmation I was fishing for in that post. . .

--

Mike and everybody - do you think the recent Titan raws have got blander than usual (as happened once before when they changed some contrast setting) or is it just the terrain we're looking at here?

Quick question, my Titan map is a bit outdated (2006). Where can I find the most up-to-date Titan map?

http://photojournal.jpl.nasa.gov/catalog/PIA08399

I think Jason did this. Not sure if it's been updated recently.

I've been wondering if they changed the way that they stretch the image when creating the raw image .jpeg files.

Another key factor may be the phase angle. The higher the phase angle, it *seems* the lower the contrast image. (I could be way wrong here, that's just been my supposition).

I was getting kinda nervous until the full-on shots from the Nov. 13 distant look showed a reassuring nice contrast.

Playing around with compensating for the frustrating gradient exposure of surface images of Titan anywhere close to the terminator, I think I've got a method that might work OK. It worked on a test image, that with a distinctive "arrowhead and chevron shape" that is just to the W of Hotei Arcus.
Click to view attachment

Here's the recipe:
Converted the raw jpegs to 16-bit images then
Stack and averaging the images
Add a grayscale gradient that approximates the shading, adding an offset and gradient such that the bright white terrain is uniform across the image and the dark terrain is uniform across the image. (Add 0 to the brightest part of the image)
Then stretch the contrast.

-Mike

For comparison, here's a version of the same image, processed with just a high-pass filter:

Click to view attachment

The issue with such processing is that it gets rid of precisely the features that we're looking for: large albedo features like the "chevron".

Here's a work-in-progress mosaic of the T47 ISS images around Hotei Arcus:
Click to view attachment

They are aligned, but not a contrast balanced ensemble. (I switched to 8-bit processing, I couldn't get a negative offset to work with the 16-bit images.)



And like it seems after every home project, there are spare parts leftover. I have no idea where this goes. (There is a similar piece in the T46 mosaic):
Click to view attachment

Any suggestions?

-Mike

Mike

I hope you or someone can figure out what the arrowheads are. I remember we saw one (radar-bright)
in TA, and it always bugged me as something interesting whose origin is not obvious...

Intriguing, but I'm not sure what arrowheads we are talking about here. If there is a common class of them worth considering as a group then it would be nice to start a catalogue of annotated images. What scale range are we talking about? Huygens landed near a couple of beautiful arrowheads but the're a lot smaller than the shapes visible on ISS images. Can you point out the RADAR one(s) you have in mind? If there is a real case to crack here I'd like to be on the volunteer team. Perhaps we need to do a sort of 'arrowhead zoo'.

go for it!.

This is from TA, shown at 128 pix/degree (i.e. 375m/pixel or so, close to the intrinsic
resolution in this part of the swath). North is roughly up. This is (eyeballing) about 700km
East of Ganesa macula

Evidently acquired too long ago - isnt radar-bright after all; radar dark (compared to immediate
surrounds..)
Click to view attachment

Aah right. It does jump out at you, I agree. However I can't see much difference between the ground inside the V and outside to the right of it. Perhaps the right stroke of the V is the 'feature' - a straightforward linear one. Cover that up and the rest of the area reverts to quasi-random (fractal) light/dark boundaries. It will be interesting to look for more, though.

Also maybe Mike or one of the others who did so well analysing those Meridiani dunefields might be able to answer the question: How many 'arrowheads' would we expect to find in the Titan images through chance alone, without a special cause? I would guess a few, given that linear streaks and linear boundaries seem to be fairly common.

Leaving the maths to the experts, I will when I get home empty a box of matches on the carpet and count the V's. I'll also take note if any happen to coincide with patterns on the carpet in a 'suggestive' way.

Results here later.

Back to the T47 flyby...

I modified my method to deal with the gradient of Titan images near the terminator. Here is my latest processing of the T47 Hotei Arcus images side-by-side with my older 8-bit image:
Click to view attachment

Recipe:
Converted the raw jpegs to 16-bit images then
cosmic ray hit removal - Add median filter layer for each image, median filter 2 pixel, set layer opacity around 90%
Stack and average the images
Add a grayscale gradient that approximates the shading, (dark towards terminator, subtract 220 at brightest part of image)
Subtract the image and add a 50-100 unit offset.
Add curve layer for Anti-vignetting, add mask for AV layer (center dark, periphery bright)
Then stretch the contrast.

-Mike

Making V's -the match experiment result as promised.

100 matches scattered on flowery carpet: just one well-formed V (defined as match ends meeting neatly at an acute angle). No correlation with carpet albedo features.

Nice work with Hotei Arcus images Mike.

Here is the latest version of my work-in-progress T47 SE Xanadu Mosaic.
(I found where the missing piece went: one of the wide angle images gave me the clue)
Click to view attachment

These images were gradient corrected in Photoshop. The mosaic was constructed in Powerpoint. It turns out Powerpoint 2007 has a handy feature that allows contrast and brightness adjustment of imported images.

-Mike

Here's a wide angle view of SE Xanadu-Hotei Arcus that I used to line up some of the images.
I labeled some of the features you can see in the image:
Click to view attachment

The Feature I'm calling "The Pinecone" is extremely helpful and distinctive for orienting and lining up some of the images. Weird how it's embayment pattern is NW-SE - very different from surrounding terrains - like it's a rotated block or something....

And here is the latest version of the work-in-progress mosaic of the ISS images around Hotei Arcus from the T47 flyby:
Click to view attachment

-Mike

Final version T47 SE Xanadu-Hotei Arcus ISS Mosaic + PIA08399 crop as basemap:
(ca. 45% of the highest resolution T47 image)
Click to view attachment

-Mike

The VIMS ridealong version of this mosaic will knock your socks off! -- at least it will when I'm allowed to show it, which unfortunately won't be until we get a paper out or 2009 October 1, whichever comes first

- VIMS Jason

PS -- sorry for the tease!

I'll make a wild guess: (And I don't expect and answer, I'll wait until the paper comes out...)

Something I've been suspecting for a while...

[wild flaming speculation]
Hotei Arcus is an ancient impact crater. The impact punched through to a subsurface water/ammonia layer and created a permanent hotspot under Xanadu. The resulting Hotei Acrus cryocaldera is a large source of the dark lobate flows that would be best described as flood cryobasalts. The flood cryobasalts oozed and crept their way down the valleys and infilled lakes and valleys.

(Similar stuff was proposed on Earth to explain some of the antipodal hotspots on our planet, including Yellowstone and the Columbia River flood basalt province, check out: Hagstrum, J.T. Earth and Planetary Science Letters 236 (2005) 13-27. "Antipodal hotspots and bipolar catastrophes: Were oceanic impacts the cause?" doi: 10.1016/j.epsl.2005.02.020. Freely available here.)

So Hotei Arcus is a Titan version of Yellowstone and the Columbia River Flood basalts, but without the continental drift.

Intermittent hydrocarbon run-off ran down into the cryobasalt terrain and left their own pattern imprinted on the basalts, evidenced by RADAR-bright channels with jagged kinks. (Compare with the sloughs up in the north polar area: you'd expect such a wide sediment filled valley to contain a RADAR-dark winding slough.)

(Also check out the middle of T7: There is a large (kinda brightish) flat area that the stream curves around. Is this the contact between a flood basalt outpouring and softer terrain?)

Menrva is a failed Hotei Arcus: The Menrva impact did activate some cryovolcanic activity, but it was relatively short lived. (Explaining the uplifted dome in the SW corner of Menrva, the bulgy, zitty appearnce of the central portion of Menrva, and possibly the rough flow pattern to the E.) Later, sediments infilled the lower ring of the crater basin through a breach in the rim apron on the SW side.

Prediction for VIMS data for Hotei Arcus? The cryovolcanic flood basalts are composed of VIMS bright blue unit: These are sandwiched in valley walls of VIMS Equatorial Bright terrain. These bright blue valley constrained flood basalts might not have been large enough to have been picked up the lower resolution VIMS mapping (seen in Jason's avatar).
[/wild flaming speculation]

Anyone else wanna guess?

-Mike

Wonderful news Jason.

Mike your guess sounds reasonable to me, at least in general terms. I suppose we'd have to assume that the impact itself was very ancient. I'm not sure how a 'permanent hotspot' would work, but I could envisage a permanent weak area of crust that could be reactivated by subsequent energy inputs unrelated to the impact. These could include heating or mechanical stress arising from global internal (phase change?) processes or purely crustal deformation arising from reorientation episodes (polar flops). I hope we will learn conclusively whether activity continues up to the present time.

EDIT- a reminder that weak crust can be reconciled with elevated topography if the density is low, and we already have RADAR evidence that Xanadu is 'porous'.

I'm wondering if there is something 'special' about Xanadu that primed it for oozing cryolava. (And for making dramatic scenery).

Some sort of crustal weakness, preexisting "bulge" that got relaxed back, different materials to start with, etc.

One compositional possibility might be a higher than average fraction of dissolved or clathrated (is that a word?) volatiles. I'm imagining a material that behaves a bit like foam filler from a spray can - frothing up and setting when presssure is removed. It seems to me that the volume change associated with such a process could produce some pretty wild - and porous - topography. Any external disturbance (like an impact) that exposed new surfaces would induce a frothing fit.

Possibly resulting from a deep,deep core-mantle layer hotspot?

IIRC, methane is percolating up through the mantle and high pressure ice layers from the core, fizzes through the subsurface ocean, then percolates into the crustal ices. (Possibly clathrating at the water/crustal ice boundary).

-Mike

I thought about that. That's the problem with these ocean moons. They've each got, as it were, another world nested inside with it's own geography and history. You can always invoke asymmetry of the inner world to explain asymmetry of the crust but that pushes the whole issue beyond observational control, at least for the immediate future. My very tentative feeling is that anything fizzing up steadily into the ocean from below would pretty quickly mix and distribute evenly throughout the ocean. Also I doubt that any one point on the crust has remained over the same interior location throughout Titan's history. These are the reasons why I think a 'permanent' hospot on the surface is unlikely. I could more easily accept the sort of process you describe if it took the form of a comparatively short-lived convulsive episode - but even so it's pretty untestable.

I wonder if something like this could show up as a gravity anomaly and be detectable by Cassini flyby trajectory information. A large blob of warmer stuff near the core should be less dense than surrounding material.

I know this is really, really wrong, but I keep looking at Xanadu and the graben of Shiwannae Virgae and imagining the Tharsis bulge and Valles Marineris. (dand near the same orientation too.)

-Mike

Well a couple of major differences come to mind:

Mars is (mostly) solid, hence surface features cannot drift relative to the interior, and the crust is rigid enough to support Tharsis as an overburden.

Titan's crust is free-floating and relatively plastic, so presumably the features are close to isostatic equilibrium.

Gravity may tell us something, but I doubt if it will be enough to constrain Titan's interior structure unambiguously. I think that will require a global seismic network. (So I hope some of the answers we're after turn out to be less deeply buried!)

I've got another guess for the VIMS data of Hotei Arcus:

The VIMS of the ISS dark lanes will show it to be the Deep Black VIMS unit: dark thermally processed organic tars blooped up from the subsurface crustal layers.

This would make Hotei Arcus the flood basalt version of Omacatl Macula. (Omacatl Macula being like a tar geyser)


So my two guesses are for one of the two "ends" of the VIMS terrain unit spectrum. Either the bright blue unit (purest ice) or the deep black unit (gnarliest organic tars). Both guesses imply extensive thermal processing of Titan stuff.

I'll be watching Jason's rotating VIMS globe avatar carefully to see any subtle changes over the next few months.....

-Mike

Jason...

Any chance of a peak during the AGU next week? If not, paper ASAP please!!!!

Craig

*sigh* -- I'm afraid that "ASAP" for us means at least 6 months! The whole process just takes that long. But I'll post it here as soon as we've got something.

I'll have to miss AGU this year because I'm teaching, so I'll be following it here on UMSF just like everyone else this time

- Jason

That...is...just...so....cool.

You rock!

Here is a zoom of the completed T47 SE Xanadu - Hotei Arcus Mosaic with the T13 RADAR Swath blended in:
Click to view attachment

(For the RADAR Swath, this is approximately 1.4 km/pixel resolution)
The dark lane at the top of the T13 Swath correlates to a slightly-darker-than-surrounding lane in the T47 ISS images.

The more I stare at this, the more I really, really like the flood cryobasalt idea:

The darker arc shape to the NE of Hotei Arcus is dark in both the ISS and RADAR. But as you work your way up the arc shape counterclockwise into the T13 Swath area, the dark zone yields to lighter toned terrain with a continuing arc shape pattern. This would imply that the lower reaches are embayed and the upper lighter tone terrain is not, suggesting topographic control. (The regional gradient is to the S, as evidenced by the bright channels).

It seems likely that some of the darker spots closer to Hotei Arcus are similar embayed lowlands similar those seen in the T13 Swath.
(It is not clear if RADAR-dark always correlates to ISS dark in Xanadu.) (Note how jagged RADAR-bright streams cross the embaying material.)

A higher quality version can be downloaded here (same resolution).

-Mike

Thank you Sir!!!

I understand that ASAP in this case means time. We are so spoiled any more for 'instant results'. I look forward to having my socks knocked off!!!!

And I must say I appreciate all the input from all the researchers, and operations folks, and engineers, etc., who contribute on this forum.

You all rock!!!!!

Craig