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The two faces of Titan's dunes
ngunn
post Jan 23 2012, 08:38 PM
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ESA press release today: http://www.esa.int/esaCP/SEMX5NH8RXG_index_0.html
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ngunn
post Jan 23 2012, 11:13 PM
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No comments? OK I'll post one. This is a fact-reporting article (observations, correlations) and at that it succeeds perfectly. It offers a tentative tying up of a number of loose ends. To me that's less convincing because we don't have all the ends yet so tying ends up now may mean making wrong connections. Lots of questions beckon, as always with Titan. If the dune material descends from the hydrocarbon haze this presumably happens at all latitudes, so what happens to it north and south of the tropical dune zone?
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Juramike
post Jan 24 2012, 01:18 AM
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Atmospheric sintering is just one of the possible ways of making dune particles.
(Remember, it's still not known exactly what is in the dune particles. RADAR dielectric constant suggests 'organic' (not ice).
VIMS, which only sees the first few microns, suggests some aromatics with benzene-like stretches near 5 micron are present?) To really determine composition, some type of in-situ separation/then characterization would be needed. (LC-MS/MS Orbitrap). This will be a really neat problem for a future mission.

Even uglier, atmospheric chemistry on Titan isn't the same everywhere. Some recent CIRS data shows that the concentrations of different atmospheric materials vary widely by lattitude (multiple orders of magnitude). So the starting ingredients for the atmospheric chemistry is different in different locations. That could also have an effect on what gets constructed in the atmosphere and then deposited on the surface.

So you'd want to send that LC-MS/MS Orbitrap down to different places. Titan's surface will taste different depending on your location. That might be one possible explanation for polar zones being different than equatorial zones.


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titanicrivers
post Jan 30 2012, 07:26 AM
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QUOTE (ngunn @ Jan 23 2012, 05:13 PM) *
... Lots of questions beckon, as always with Titan. If the dune material descends from the hydrocarbon haze this presumably happens at all latitudes, so what happens to it north and south of the tropical dune zone ...

and of course in the Xanadu region which lies WITHIN the tropical zone at a LOWER elevation than the surrounding dune seas and presumably is OLDER geologically than the dune fields!
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ngunn
post Jan 30 2012, 01:18 PM
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QUOTE (titanicrivers @ Jan 30 2012, 07:26 AM) *
and of course in the Xanadu region which lies WITHIN the tropical zone at a LOWER elevation than the surrounding dune seas and presumably is OLDER geologically than the dune fields!


We had an extended discussion about that in this thread: http://www.unmannedspaceflight.com/index.php?showtopic=5953.

See especially Ralph Lorenz's albedo-driven winds suggestion in post 11 and many posts following therefrom.
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ngunn
post Feb 26 2012, 08:07 PM
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Interesting article in Science Daily on the formation mechanism of linear dunes, with possible application to Titan: http://www.sciencedaily.com/releases/2012/...20224140615.htm
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Juramike
post Mar 2 2012, 01:24 AM
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Some more stuff on sticky longitudinal dunes (some behind a paywall, bummer):

Rubin and Hesp, Nature Geoscience 2 (2009), 653 - 658. Multiple origins of linear dunes on Earth and Titan. doi: doi:10.1038/ngeo610. Pay-for article: http://www.nature.com/ngeo/journal/v2/n9/full/ngeo610.html

An abstract discussing linear vs. bidirectional winds:
http://adsabs.harvard.edu/abs/2009AGUFM.P51G1193R

And a FREE article on Interplanetary dunes :
Bourke et al., Geomorphology 121 (2010) 114. Extraterrestrial dunes: An introduction to the special issue on planetary
dune systems. 10.1016/j.geomorph.2010.04.007 Link here.


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