Aeolian sediment mechanics on Titan: Insights from the Titan Wind Tunnel

The presence of dunes on Titan is evidence that aeolian transport is of significant geomorphic importance on the Saturnian moon. However, atmospheric and sedimentological conditions differ significantly from terrestrial aeolian and fluvial systems, the two analogous sediment transport environments that exist on Earth. Specifically, differences in the fluid viscosity, fluid-sediment density ratio, and the submerged weight of the grains appear to change some fundamental aspects of sediment transport system behaviour. Recently hardware simulation of Titan transport processes has been conducted in the Titan Wind Tunnel (TWT), located in the Planetary Aeolian Laboratory (PAL) at NASA Ames Research Center, using high pressure to alter kinematic viscosity and fluid density to approach Titan conditions. Video recorded during threshold of motion experiments show grains moving with unusual modes of both entrainment and transport. Specifically, grains are entrained through rotational, translational, or skipping motions, as opposed to near vertical ejections under ambient Earth conditions. Further, the grains are transported with greater horizontal translation than expected, deviating from the characteristic aeolian saltation trajectory. We speculate that these differences arise from a change in the relative importance of two controlling thresholds: 1) the fluid threshold, where grain ejection is controlled primarily by fluid forces; and 2) the impact threshold, where grains are ejected via forces exerted through collision with grains already in transport. This change then alters the systems response, and has implications for modelling bulk transport fluxes.