Dune length, width and orientation in the sand seas of Titan reveal regional properties

<p>Large linear dunes are found in great abundance across the equatorial regions of Saturn&#8217;s moon Titan. They are similar in width and spacing to the large dunes of the Saharan, Arabian and Namibian deserts, indicating atmospheric conditions, sand sizes and winds are comparable to those on Earth. An examination of their geomorphometric properties, such as length, width, spacing and distribution can reveal aspects of their relationship with wind strength and direction and controls by underlying topography. We traced long axes of about 70% of all measurable dunes, which involved over 20,000 measurements. We mapped all of the dunes in Shangri-La, Fensal, Aztlan, and half of the Belet Sand Sea. In addition, we measured 90,000 dune widths across Titan at 500 m intervals and fit a nonstationary statistical model with a Gaussian spatial process to determine correlations of dune spacings. Dune long axes are dominantly oriented E-W, a proxy for the sand flux and wind directions. Dunes range to over 400 km in length, with an average length of 40 km. The average length may reflect a rough spacing of obstacles, large-scale topographic variations, or the availability of sand. Dunes are directed slightly NE in the Belet Sand Sea, where dunes are especially abundant and wider. The longest dunes are also found here. Belet may thus represent a fully mature sand sea, where dunes are free to grow as long and large as possible. To the east is the Shangri-La sand sea, which is the location of the <em>Dragonfly</em> landing site. Shangri-La hosts dunes directed dramatically southward, especially near the Xanadu region margin. Dunes here are narrower and interdunes are clearly visible near the elevated rim of the Selk impact crater and other topographic obstacles. Sand collects most densely along the eastern boundary, at the margin of Xanadu, and at the downwind margins of all sand seas. This perhaps indicates that sand is transported until major boundaries are encountered that preclude sand movement. Dune width values can be divided into about 5 major (20 minor) regions globally within the sand seas, with widest groupings at the sand sea centers and isolated, narrower groupings at higher latitudes. The narrowest dunes appear to have the most obstacles or topographic control or be at the highest latitudes. However, within each cluster, dunes of any size within the 1-3 km width range can exist. These studies reveal that while local controls are impactful, dunes will ultimately grow to the extent possible under the conditions present, which on Titan are highly favorable for large linear dunes. Further examination of dune parameters can reveal details about the landscape, basement bedrock conditions, sand transport history and regional wind effects on the dunes of Titan.</p>