Lifting and Transport of Martian Dust by the Ingenuity Helicopter Rotor Downwash as Observed by High-Speed Imaging From the Perseverance Rover.

Martian atmospheric dust is a major driver of weather, with feedback between atmospheric dust distribution, circulation changes from radiative heating and cooling driven by this dust, and winds that mobilize surface dust and distribute it in the atmosphere. Wind-driven mobilization of surface dust is a poorly understood process due to significant uncertainty about minimum wind stress and whether the saltation of sand particles is required. This study utilizes video of six Ingenuity helicopter flights to measure dust lifting during helicopter ascents, traverses, and descents. Dust mobilization persisted on takeoff until the helicopter exceeded 3 m altitude, with dust advecting at 4-6 m/s. During landing, dust mobilization initiated at 2.3-3.6 m altitude. Extensive dust mobilization occurred during traverses at 5.1-5.7 m altitude. Dust mobilization threshold friction velocity of rotor-induced winds during landing is modeled at 0.4-0.6 m/s (factor of two uncertainty in this estimate), with higher winds required when the helicopter was over undisturbed terrain. Modeling dust mobilization from >5 m cruising altitude indicates mobilization by 0.3 m/s winds, suggesting nonsaltation mechanisms such as mobilization and destruction of dust aggregates. No dependence on background winds was seen for the initiation of dust lifting but one case of takeoff in 7 m/s winds created a track of darkened terrain downwind of the helicopter, which may have been a saltation cluster. When the helicopter was cruising at 5-6 m altitude, recirculation was seen in the dust clouds.
(© 2022. The Authors.)