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 feedbacks betweenatmospheric dust distribution, circulation changes from radiative heating and cooling driven bythis dust, and winds that mobilize surface dust and distribute it in the atmosphere. Wind-drivenmobilization of surface dust is a poorly understood process due to significant uncertainty aboutminimum wind stress, and whether saltation of sand particles is required. This study utilizesvideo of six Ingenuity helicopter flights to measure dust lifting during helicopter ascents,traverses, and descents. Dust mobilization persisted on take-off until the helicopter exceeded 3 maltitude, with dust advecting at 4-6 m/s. During landing, dust mobilization initiated at 2.3-3.6 maltitude. Extensive dust mobilization occurred during traverses at 5.1-5.7 m altitude. Dustmobilization threshold friction velocity of rotor-induced winds during landing are modelled at0.4-0.6 m/s (factor of two uncertainty in this estimate), with higher winds required when thehelicopter was over undisturbed terrain. Modeling dust mobilization from >5 m cruising altitudeindicates mobilization by 0.3 m/s winds, suggesting non-saltation mechanisms like mobilizationand destruction of dust aggregates. No dependence on background winds was seen for theinitiation of dust lifting, but one case of takeoff in 7 m/s winds created a track of darkened terraindownwind of the helicopter, which may have been a saltation cluster. When the helicopter wascruising at 5-6 m altitude, recirculation was seen in the dust clouds.