Mathematics – Logic
Scientific paper
Oct 2007
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007dps....39.5702r&link_type=abstract
American Astronomical Society, DPS meeting #39, #57.02; Bulletin of the American Astronomical Society, Vol. 39, p.531
Mathematics
Logic
Scientific paper
The thousands of dunes that cover 7% of Titan's observed surface ( 20% of Titan's total surface if extrapolations are valid) [1,2] are an indication of unique geological conditions necessary for their formation and persistence. There must be sufficient sand supply, and because dunes are dark to Cassini Radar (2.17 cm), ISS, and VIMS (both NIR) [3] it is presumed the dunes are composed of mostly organic particulate "sands". Winds must be sufficiently strong to initiate and maintain saltation of these particles in dune regions ( 1 m/s [1]), mainly within +-30 degrees latitude. Nearly all dunes observed on Titan are longitudinal, and thus require one of several proposed conditions for wind direction and timing. Based on dune orientations and divergence around topography, as well as other features such as bright materials trailing behind obstacles, the best model is the prevailing wind hypothesis, in which winds blow parallel to the dune long axis [e.g. 4,5,6]. In Titan's equatorial regions, these winds are best explained as dominantly Eastward [1,2]. Some features indicate a two-wind, or resultant model may operate in some regions, in which two winds blow slightly oblique to the dune long axis [e.g. 7,8]. These features include increased dune sinuosity (particularly at higher latitudes), characteristic of dunes on Earth that form by this model. Finally, the formation and persistence of dune fields require the regions to be generally dry and free of sediment-trapping lakes and streams. All lakes and presumed-full streams have thus far been observed in the polar regions [9], distant from dune fields.
[1] Lorenz e.a., 2006. [2] Radebaugh e.a., in revision. [3] Soderblom e.a., 2007. [4] Blandford, 1877. [5] Folk, 1971. [6] Fryberger and Dean 1979. [7] Tsoar, 1983. [8] Lancaster, 1982. [9] Stofan e.a., 2007.
Allison Michael David
Boubin G.
Callahan Philip
Cassini RADAR Team
Kirk Randolph L.
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