Ongoing Measurements of Dune Width and Spacing on Titan Reveal Dune Field Properties
Résumé
Introduction: Saturn's moon Titan is home to many landforms similar to those found on Earth. One of Titan's most notable landforms are dune fields, which cover perhaps 20% of Titan's surface [1-5]. These dunes are linear in form and can stretch to hundreds of kilometers in length [6]. They are located in equatorial regions and can be found between latitudes of ±30º [1,2,4,5]. Modeling of dune parameters on Titan, such as dune width, spacing, and length have yielded important results concerning dune field maturity [6-8]. The emerging pattern analysis results and the uniformity of dune form across Titan indicate these dunes may be in an equilibrium condition that has persisted for a long time [8]. The duration of aeolian dune processes on Earth is also relatively long lived [9], so how Earth-like processes relate to those on Titan is the subject of current study [7-10]. The following are results from a pattern analysis study of Titan's dunes, presented along with a new method for measuring crest spacing of Titan's linear dunes. Methods: New measurements of dune width and spacing have been obtained, using Cassini Synthetic Aperture Radar (SAR) in the USGS program ISIS, for two main sand sea regions. The first is in the Fensal Sand Sea, east of Xanadu, with measurements so far from the T25 swath (20º S -20º N, 32º W -49º W, Fig. 1a,b) and the second is from the Belet Sand Sea, the 2500 km long collection of sand west of the Xanadu terrain, with measurements so far from the T8 swath (5º S -10º S, 189º W -315º W). This is a continuation of a previous study, in which dune width and spacing were measured in various locations in six different SAR swaths across Titan [8] and build on similar measurements by Le Gall et al. [4]. The Savage et al. [8] study utilized measurements obtained at approximately 5 km intervals, yielding ~7,000 each width and spacings [8]. Dune widths were measured from one light/dark boundary to the next across SAR-dark areas perpendicular to the long axis of the dunes. After widths were measured, interdune spacing was obtained for each region using the same method, across SAR-bright areas. Crest-to-crest dune spacing was approximated by adding the average dune width for a particular degree of latitude to the average interdune spacing for that same degree of latitude [8]. These methods were used because Cassini SAR resolution (~300 m.) is not good enough to distinguish actual dune crests. Current measurement methods differ from those of Savage et al. [8] in that crest-to-crest spacing is now done by measuring from one SAR light/dark boundary to the next SAR light/dark boundary perpendicular to the long axis of the dunes (Fig. 1c). Dune widths were measured as in [8], across each dark feature (Fig. 1c), and width and spacing was measured from the same starting point (Fig 1c). We believe this will provide us with a more accurate measurement for crest spacing, and will enable us to precisely correlate dune width and spacing.