A laboratory study of sediment flux within dust devils on Earth and Mars

Laboratory experiments using the Arizona State University Vortex Generator (ASUVG) were run to estimate sediment flux in dust devils on Earth and Mars. Particles of different sizes and densities were utilized in dust devil simulations at Earth and Mars atmospheric conditions to determine trends in sediment flux by measuring the mass loss as a function of time and size of the vortex. Characterization of the effects of non-erodible roughness elements on vortex flow, particle threshold, and sediment flux was also conducted. Laboratory sediment fluxes were used with in situ lander data and orbiter image statistics on dust devil distributions to estimate average sediment fluxes from five sites on Mars.;Sediment flux results showed that dust particles (less than 62 microns) are more easily lofted in dust devils than sand particles (62-2000 microns). Laboratory sediment fluxes ranged from 1E-6 to 1E0 kilograms per square meter per second when no roughness elements were present. Roughness elements resulted in lowered efficiency of the vortices leading to increased particle thresholds and decreased sediment fluxes for experiments involving medium- and high-density roughness arrays. However flow was enhanced for low-density roughness arrays (small elements) allowing lower thresholds and increased sediment fluxes led to the concept of an "optimal roughness" for dust devil sediment lifting. Laboratory results of dust devil sediment fluxes were used to estimate sediment fluxes from landing sites and sites with orbital images of dust devils. Laboratory sediment flux estimates yielded a range of 0.5 to 45.0 kilograms per square kilometer per sol depending on sediment availability, dust devil activity, surface roughness, and gravity differences between Earth and Mars. The results suggested that dust devil sediment flux input to the martian dust cycle could vary from region to region.