SAND DUNES ON TITAN AND PLUTO AS REVEALED BY REMOTE SENSING MORPHOLOGICAL AND FIELD ANALOGUES

Sand dunes observed across the solar system are often discerned and classified based on their resemblance to dunes on Earth, even though the landforms form under different atmospheric conditions, sand compositions and time scales. While it is important not to categorize features based on a few similarities – for example, linear dunes are long and sub-parallel, with bifurcating junctions, as are ripples – it is wise to rely on a compendium of morphological evidence, when present, to lead to important conclusions about the origin of features.

Dunes on Titan are large, linear features that interact with topographic obstacles and are the same size and shape as large linear/longitudinal dunes of Earth’s big deserts. A comparative remote sensing study of dunes in the Namib Sand Sea and those in Titan’s Belet Sand Sea reveals that dune width and spacing increase toward the sand sea center and with increasing elevation, while similar relationships are not observed in Belet. Given the Belet Sand Sea is 100x the size of the Namib, further subdivision of the Belet may yield stronger associations. Field studies in the Namib using Ground Penetrating RADAR revealed that sand is transported along the dune long axis. This is consistent with observations of dunes interacting with obstacles, both on Earth and Titan, and with recent models predicting growth by this mode of transport.

Collections of linear features at the base of the Al-Idrisi Montes on Pluto demonstrate regular spacing, bifurcations, pattern coarsening toward the centers of the collections, and reorientation with changing predicted surface winds. Similar morphologies are seen in the Mesquite Flats dunes of Death Valley, also at the base of mountains. Sands for the Mesquite Flats dunes are sourced from the mountain fans, and it is possible the mountains are also the source of Pluto’s sands, likely methane ices. Future studies of planetary landforms should continue to incorporate important field and morphological analogues from Earth and other planetary surfaces.