Optical Depths of Dust Devils Observed in Gale Crater, Mars

Abstract

The Mars Science Laboratory (MSL) Curiosity Rover has detected dust devils using the on‐board Navigation Cameras (Navcam) and the Rover Environmental Monitoring Station (REMS) throughout the MSL mission. While previous studies have quantified the frequency and location of dust devils, their optical depth and how it changes with time, season, and location is still unclear. In this work, we derive the optical depths of dust devils imaged with Navcam to understand the factors influencing their optical depths. We find that dust devil optical depths have a minor seasonal dependence with substantial interannual variability. Diurnally, dust devil optical depth is highest between 11–14 local true solar time (LTST), and lower in the morning and evening. Comparisons with REMS convective pressure vortices indicate that, while a higher number of pressure vortices correlates well with a higher number of dust devils, stronger pressure vortices are not fully consistent with high optical depths. By examining the dust devil optical depth through the rover's traverse, we see that surface properties may be a factor influencing dust devil optical depth, where the highest values are observed in low thermal inertia locations with sand patches, such as the Bagnold Dunes and the Sands of Forvie. Overall, these results indicate that dust devil optical depth is influenced by a combination of seasonal, diurnal, and environmental factors that likely act together to produce the observed variability.