Printable Version of Topic

Posted by: ngunn Dec 12 2006, 06:30 PM

Mountains on Titan - news via jupiter list:
http://tech.groups.yahoo.com/group/jupiter_list/message/7565
Edit: Shouldn't be in T21 thread - don't know how to move it though.

Posted by: volcanopele Dec 12 2006, 06:41 PM

Massive Mountain Range Imaged on Saturn's Moon Titan
http://saturn.jpl.nasa.gov/news/press-release-details.cfm?newsID=709

I'm not so sure I agree with their conclusion, but they seem to think that based on the appearance of the dark "stuff" to the east of the bright streaks at different wavelengths, that that dark "stuff" is topographic shading and that the bright streaks are mountain chains. I am not sure I agree with that statement. I can't go into detail why, but I think bright streaks are some kind of "stain" on the surface, not topographic.

The more interesting news is the statement:

VIMS was able to resolve the dunes and able to see the compositional differences between the dunes and the inter-dune regions.

Posted by: alan Dec 12 2006, 07:32 PM

I've been looking forward to seeing something like this:
http://photojournal.jpl.nasa.gov/catalog/PIA09035

volcanopele: what direction does the wind blow on the Titan's surface?

Posted by: ugordan Dec 12 2006, 07:34 PM

Westward.

Posted by: AlexBlackwell Dec 12 2006, 07:36 PM

And I was going to say "leeward."

Posted by: volcanopele Dec 12 2006, 07:40 PM

West to east

Posted by: ngunn Dec 12 2006, 08:45 PM

Thanks for posting the proper link.
Are you questioning the whole mountain range idea or just a more subtle aspect of their interpretation?
Does the 3D appearance of the 'mountain' image arise from processing based on an assumption about the topography or is it intrinsic to the data?

Posted by: volcanopele Dec 12 2006, 08:48 PM

They could be mountain ranges, but I question that they are seeing topographic shading, which underpins their mountain interpretation. I think the "3D" appearance arises from the pattern of bright-dark material in that region that makes it look like some of the dark material is actually topographic shading.

Though this image, http://saturn.jpl.nasa.gov/multimedia/images/image-details.cfm?imageID=2381, is really good for having been taken from 12 billion km away

Posted by: ngunn Dec 12 2006, 09:09 PM

It is, isn't it! Looks a bit lke that thing on Iapetus.

Posted by: helvick Dec 12 2006, 09:17 PM

Very clever of them to put such a good instrument on Voyager 1

Posted by: JTN Dec 12 2006, 10:47 PM

There's an http://wwwvims.lpl.arizona.edu/2005-03-31.T4_dunes.jpg supporting this (side-by-side comparison of radar and VIMS) that appears on the http://wwwvims.lpl.arizona.edu/whatsnew.html (caption is near the bottom), but not on the JPL site, for some reason. (The same region with VIMS overlaying radar is http://saturn.jpl.nasa.gov/multimedia/images/image-details.cfm?imageID=2385, but the caption doesn't mention the dunes.)

Posted by: Jason W Barnes Dec 13 2006, 03:29 AM

I guess I shouldn't be surprised to find that this group picked up on the newly released VIMS T20 images so quickly!

Originally the RADAR/VIMS with the dunes there was supposed to be an animated .gif blink, I thought, but maybe we were going overboard with the blinks, so they just released the straight VIMS over RADAR comparison. I kind of like the blink version better, as it seems to be the best way to intercompare the two. Did you see the sinuous red streak near the RADAR circular feature in the lower left? Better than 400m resolution -- we're getting down toward the scale of flows on, say, Mauna Loa.

Posted by: Jason W Barnes Dec 13 2006, 03:46 AM

Aha -- you have to go into the 'full-res' part to get the blinks. Here are direct links to them:

http://photojournal.jpl.nasa.gov/archive/PIA09034.gif

http://photojournal.jpl.nasa.gov/archive/PIA09036.gif

Posted by: ngunn Dec 13 2006, 10:45 AM

Thanks Jason B. Can you (or anyone) answer the question I put (not very clearly) to the other Jason? it's about the 'mountains' image. Has there been any reprojection of the image following 'draping' over inferred topography?

I suspect the answer is 'No' but just want to be sure.

Posted by: Matt Dec 14 2006, 01:41 AM

I hope this is correct about the taller mountains, because I was always very fond of the orographic interpretation regarding those mid-southern latitude clouds.

They sound pretty conclusive about it.

Posted by: Jason W Barnes Dec 14 2006, 03:16 AM

Correct; there's no draping. If we only knew the topography so that we *could* drape it! Getting topography on Titan has proven very difficult. The only places where we have a good handle on it are near the landing site, where there's some limited stereo coverage, and the few places where we have 1-D RADAR altimetry tracks.

Posted by: ngunn Dec 14 2006, 10:18 AM

Thanks. I now look forward to sometime hearing more from 'volcanopele' about why he doubts the mountains (which look pretty convincing - at least to this particular layman).

Posted by: remcook Dec 14 2006, 12:09 PM

If you don't know or can't derive the topography, you can't distinguish between shading and mere dark spots on a flat surface at any one instance- I think. It would be interesting to see the terrain at various local times and see if there's movement (shadows). Or for radar, different incident angles.

I think it looks strange (I am a complete layman in geology so maybe it's not strange at all!): It looks kind of like a mountain, but then there doesn't seem to be any correlation with the dark-light pattern of the 'continents'. I would expect the appearance to correlate with altitude, but that doesn't need to be the case of course. So it looks to me, layman, that either the 'mountains' are streaks that are laid on top of the 'continents' (so no real mountains, or that 'continents' are deposited from the atmosphere on top of real topography (the mountains). But then you would expect the 'continents' to be changing, which they are not. hmmmm

Anyway, enough rambling from me

Posted by: ugordan Dec 14 2006, 01:35 PM

Jason W. -- have any successful attempts at deducing topography from methane absorption been made? Or is the data too noisy to pick up miniscule decreases in atmospheric column height over high topographic points? Especially since Titan's atmospheric scale height is very large and topography comparatively subtle.

Posted by: ngunn Dec 14 2006, 03:11 PM

On the contrary that was a really good ramble! Here's some more: We know from Huygens that IR albedo sometimes correlates with topography. We also know that IR albedo sometimes correlates with radar, but that there are areas both large and small where this correlation is completely absent. We know that both ices and organics can be either dark or light, and (independently) either high or low. We suspect that both the surface markings and the topography arise from both weather and cryovolcanism, and that some of the weather is indeed related to releases of methane (and what else?) from the interior. However we are pretty ignorant of the time scales for all of these processes. With so many possibilities I find it hard to say that I 'expect' anything in particular just yet. As to the patchwork effect on the 'mountains' - Think of a mountainous area with complex geological history, such as North Wales where I live. I've seen a geological map of this area printed onto a plastic relief model. The result was pretty much patchwork mountains.

Posted by: volcanopele Dec 14 2006, 04:21 PM

remcook hit the nail on the head, I'm unconvinced they are seeing topographic shading. As remcook states, I would be more convinced if additional views of these features at different incidence angles (think time of day) were taken. Then we can see if the dark material just east of some of the bright streaks is from topographic shading or just dark stuff on the surface.

Now, these could still be mountains. The fact that they are much brighter than the surrounding terrain could be due to material condensing at high altitude. If they are mountains, they could be similar to the mountains seen in eastern Adiri by RADAR during T8 (see http://photojournal.jpl.nasa.gov/catalog/PIA03566).

Posted by: ngunn Dec 27 2006, 04:00 PM

Just noticed Emily has a nice 26 Dec. update on the alleged Titan mountains on her Planetary Society blog. It addresses nicely some of the worries I had about the physical difficulty of observing topopgraphic shading on a hazy world, but sails breezily over the issue of surface markings failing to match topography - the main(?) cause of scepticism on the part of volcanopele and remcook.