Wind Tunnel Experiments as an Analog for Sediment Motion in Planetary Systems

Wind shapes the surface of a wide range of planetary bodies, from Earth, to those known for their dense atmospheres (such as Venus and Titan), to those with relatively thin to ephemeral atmospheres (such as Mars, Pluto, and Comet 67P/Churyumov-Gerasimenko). Sediments transported by the wind range from quartz and basalt sands to exotic materials such as grains of ice and organics. Several wind tunnel and field experiments have formed the basis of our understanding of particle motion initiation and cessation, but these initial studies were limited to terrestrial boundary conditions and materials. Recent work has demonstrated that extrapolating the results of models generated using terrestrial data to other planets, such as Mars or Titan, results in inaccurate predictions of particle motion.

Previous work has relied on a combination of using analog sediments and altering fluid density, though results remain inconsistent with in-situ observations. Taking a different approach, we use low-density spherical grains at ambient gravity, atmospheric density, composition, and pressure. We employ a combination of custom-produced and commercially available plastic grains. Using scaling parameters from previous studies, materials such as table tennis balls are being used as analogs for sediment transport of organics on Titan and nitrogen ice on Pluto. With 3D printing, we are able to produce grains of specific densities and scales, with parameters chosen to replicate the balance of forces experienced by grains in extraterrestrial systems. This study aims to generalize the expressions for threshold velocities to accurately represent motion initiation in a range of conditions.