Titan's topography, strange.... Options

[titanicrivers]

Should note that the T50 swath found no correlations between rough terrain (or changes in radar brightness) and those near-IR bright streaks.

Yes that was a bit disappointing! And didn't a later VIMS image seem not to suggest mountains? Still there seems to be an uplift in the general topography going from South to North. (maybe explaining all those Ethane rain showers in Yalaing terra VIMS has been seeing! )
http://www.planetary-science.com/content/2/1/1

[titanicrivers]

Yes that was a bit disappointing! And didn't a later VIMS image seem not to suggest mountains? Still there seems to be an uplift in the general topography going from South to North. (maybe explaining all those Ethane rain showers

I wanted to include this outstanding article as well ... too bad VIMS didn't have a quality view of Yalaing terra on Dec 20 2010 when possible liquid ponding in central Yalaing was present.
http://www.readcube.com/articles/10.1186/2191-2521-2-1

[ngunn]

perhaps VP can update his Radar Swath Maps again and get bothT83 and T84 entered.

I've just noticed that he has. Thanks Jason.

EDIT: And on T83 there are more spactacular 'New Wrinkles'-like features in 'Hot Cross Bun' land. No doubt titanicrivers will do a fine job of integrating this with the other swaths and topography.

[titanicrivers]

Thanks for T83 and T84 VP! Agree with ngunn this is a fascinating area in the topography of the mid northern latitudes of Titan. Perhaps this is a cryovolcanic province with constructs of varying ages and degrees of erosion. The drawing places T64(left) with the 'new wrinkles' terrain and T83 (right) with the 'hot-cross-bun' possible volcanic construct and as Nigel points out, other roundish structures enclosing radial SAR density highlights. The T64 SAR has topographic and geomorphic unit maps http://www.lpl.arizona.edu/~rlorenz/titantopo/ superimposed, while T83 has not been analyzed in this way as yet (to my knowledge at least).

[ngunn]

It is a fascinating and unusual patch of ground, no doubt about it, but I'm cautious about inferring volcanism. Diapirism only requires a density inversion and materials capable of plastic flow. A heat source is helpful but not essential. I can imagine that different kinds of clathrate saturated to varying degrees with organic fluids might produce these features without being heated from below, in the same way that salt domes form in Earth's sedimentary provinces.

[Gerald]

Not quite shure, whether it's the best possible thread to post, but the contents of Cassini Data: Saturn Moon May Have Rigid Ice Shell is topography-related. So I'll post it here:

The researchers were surprised to find a counterintuitive relationship between gravity and topography.

"Normally, if you fly over a mountain, you expect to see an increase in gravity due to the extra mass of the mountain," said Nimmo, a Cassini participating scientist. "On Titan, when you fly over a mountain, the gravity gets lower. That's a very odd observation."

A possible interpretation is described in the referenced release.

[ngunn]

Nimmo has an agenda - to show that Titan has no internal activity. Whilst not denying that possibility, I'm suspicious of interpretations that come from such a starting point. Titan's mountains could be made of foamy low-density material. There should be no expectation for them to have a particular gravity signature either way.

[Gerald]

So the surmised topography - gravity - correlation needs to be verified. Thanks!

[Juramike]

Another interpretation is that Titan had a lot of erosive activity. So the lower gravity signature is a kind if remnant from when it had isostatically compensated mass.

The mass up higher is more detectable than the mass down below the ice shell. So if you shave off the top (erosion), you feel less mass during the flyby than you'd expect. At least that is how I understood it.

[nprev]

So, Mike, by implication then Titanian mountains don't have 'roots' like the mountains of terrestrial planets?

This place just seems to get weirder all the time. Love it!!!

[Juramike]

So here's some of the really weird stuff. (as I understand it.)

On an icy shell world with a subsurface ocean, the top is in isostatic equilibrium if the shell is thin. Load up the top, it drops down to compensate. Remove the weight, and it bobs up. Cool. (!)

Remember that ice1 (crustal ice) is less dense than water.

Here is where it gets weird. On a terrestrial world, if you heat up the mantle, it expands and rises up. And boom. Mountains.

On an icy world, if you heat up the bottom of the crust (no clue how, just run with it.), you melt the ice, lower the average density, and the top part sinks down to compensate.
If you cool the bottom, (higher thermal flux through the crust somehow), you freeze out more ice on the bottom, since it is less dense, the local density decreases, and the top of the crust should bob up.

Think of it like throwing a beach ball into a scummy pond. The ball bobs back up, but drags up the mat of algae with it. (I'd heard this analogy to describing the Olympic Mountains in Washington State).

But remember that Titan has a thick shell, (as the Nimmo et al. article states) and so does not have to be in isostatic equilibrium. It can have uncompensated mass.

[elakdawalla]

Nimmo has an agenda - to show that Titan has no internal activity.

I don't think that's Francis' agenda precisely. He's skeptical of volcanism, to be sure, but that's justifiable; there is a long history in planetary science of people pointing at features without an obvious explanation and saying "volcanism!" Consider Dione's wispy terrain and Ganymede's grooves. Or lunar craters, if you really want to go back in history. Later work tends to show things to be tectonic or endogenous in origin rather than volcanic. Francis, and also Jeff Moore (author of "Titan: Callisto with weather?") are setting up alternative explanations for features, explanations that do not require scientifically sexy active volcanism. If you're going to argue for volcanism, you have to show that it's more likely than these less-sexy possibilities presented by other workers.

The problem with Titan is that our data just aren't at that breakthrough resolution yet. We have Viking-quality data on Titan -- surface images at hundreds-of-meters resolution, one landing site that we didn't get to pick based on science. We didn't really start getting Mars until we broke through to tens or single-digit-meter-resolution image and spectral data. So the theorists and modelers still get to argue a lot about what might be happening there.

[JRehling]

I echo what Emily said and add that Mars has at least similar crustal composition to Earth. With Titan, we have meager constraints on surface and crustal composition. There has to H2O ice down there somewhere, but that's by inference rather than observation. Titan could have mountain ranges made of stuff that human beings have never observed in volume bigger than a flask, if at all. And we've already seen from small icy moons how H2O ice alone can behave in many different ways.

Titan's going to be tricky enough if we assume that all significant crustal structures consist of H2O ice. I can't even visualize what exploration pathway will be able to confirm or reject that hypothesis.

[TheAnt]

The case for a liquid subsurface ocean on Titan get stronger by these findings.
I'm surprised that the lower gravity from ice mountains can be detected, then again, they might be like icebergs in the ocean with 90% of the mass beneath. So any ice mountain on Titan might have a really large mass of ice beneath.

A bit of reading on this ice shell here.
New Cassini data from Titan indicate a rigid, weathered ice shell

[nprev]

Actually, Ant, the lower than expected local gravity over these mountains implies that there is less mass beneath them than would be expected on a terrestrial world. This is surprising and unexpected.

Hmm. "Surprising and unexpected" may be a serviceable blanket description of Titan all by itself. Fascinatingly different in almost every possible respect.