Fluid Threshold of Windblown Sand and Dust on Mars Considering Electric Field and Insolation

Abstract The fluid threshold, the wind required to move a grain from rest, is considered the critical friction velocity above which saltation begins. In this paper, the electrostatic force and the lift force of the thermal creep gas flow due to the insolation are simultaneously considered to theoretically investigate the fluid threshold of Martian grains. A model of the fluid threshold for grains saltating on the surface of Mars is derived based on the moment balance equation, which is validated with the experimental results and the prediction results of Mars Weather Research and Forecasting. It is found that the electrostatic force reduces the fluid threshold by 10.4%, and the lift force induced by insolation reduces the fluid threshold by 11.7%, and the reduction of the fluid threshold by both these forces is more significant, which enhances the dust flux by about an order of magnitude. The fluid threshold calculated by the model explains that wind‐blown sand still exists at low wind speeds on Mars observed by the Viking Lander 2, Curiosity rover and Perseverance rover. In addition, the effect of insolation and electric field on the fluid threshold is more significant when the cohesion is stochastic, and the model predicts that Martian grains in micrometer size can be lifted off the surface by the electrostatic force and the lift force induced by insolation even with no wind.