Titan's topography, strange.... |
Titan's topography, strange.... |
Apr 12 2009, 12:44 PM
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Senior Member Group: Moderator Posts: 2785 Joined: 10-November 06 From: Pasadena, CA Member No.: 1345 |
Recent article in Science by Zebker et al.:
Zebker et al. Science in press, "Size and Shape of Saturn's Moon Titan". doi: 10.1126/science.1168905 (published online April 2, 2009) Link to abstract (pay-for article): http://www.sciencemag.org/cgi/content/abstract/1168905 Article on spaceref discusses this paper: http://www.spaceref.com/news/viewpr.html?pid=27912 Figure 3 from the Science article is a global elevation map relative to barycenter. Key points of article:
"Xanadu seems to be systematically lower than other parts of the equatorial belt, and not uplifted like most mountainous areas on Earth." (quote from Fig. 3 caption in article) -Mike -------------------- Some higher resolution images available at my photostream: http://www.flickr.com/photos/31678681@N07/
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Apr 24 2009, 06:40 PM
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Senior Member Group: Moderator Posts: 2785 Joined: 10-November 06 From: Pasadena, CA Member No.: 1345 |
Link for Dorset, Acta Crystallographica B51 (1995) 1021-1028. "The crystal structure of wax."
(Pay for article; no abstract): http://scripts.iucr.org/cgi-bin/paper?S0108768195005465 The authors showed that mixed paraffin waxes after evaporation from light peteroleum ether (mostly pentanes, probably the best room-temperature terrestrial analog for liquid methane) oriented themselves into laminar sheets. When viewed from the side, the position of the carbon atoms is in a hexagonal arrangement (like a sheet of benzenes). The kinks of the chain are evidently 180 degrees out-of-phase with the chain below it. So the distance of 2 adjacent carbons is close, then far, then close as one moves along the chain. The atoms at the center of the chain are pretty locked in, but at the edges the location is more random. (Probably due to voids or other defects since these are mixed component crystals) (The structures in the article were not placed in the Cambridge Crystallographic Database). However, the crystal structure of the more complex beeswax, was much less resolved. Since one would expect multiple functionalities on Titan surface deposit materials (tholin NMR analysis indicates multiple functional groups in the mix), I'd expect that beeswax might be a better analog. [Although some of the functional groups might help orient the molecules in a crystal lattice] Another article mentions that large long chain alkanes with varying lengths compounds can orient themselves in different ways. One form which can cause large voids in the structure. http://scripts.iucr.org/cgi-bin/paper?S0108768195005465 But again, these are long straight-chain boring hydrocarbons. AFAIK, the tholin formation/deposition experiment results have been goopy smears. **** Titan's surface organics are presumably caused either by atmospheric fallout or by chemical reactions from stuff released at the surface (declathrate/reaction) or processing of stuff in hydrocarbon or aqueous solution in the subsurface. Stuff falling out of the atmosphere should be in the amorphous phase (and fluffy). It would need to be reprocessed by either solution (aqueous/organic), pressure or melting to dissolve/reorder/crystallize or reorder/recrystallize the materials. I'm not quite sure I understand the mechanism by which non-volatile dry atmospheric fallout could recrystallize/reorder at 1.5 atm and 95 K. (However, under pressure, in partial-solution, or at higher temperature the grains could agglomerate and recrystallize) -------------------- Some higher resolution images available at my photostream: http://www.flickr.com/photos/31678681@N07/
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