Suspended dust mass over time. Vertical lines mark the start of constant-speed descent (solid), visually detected dust lifting under the helicopter (dotted), and touchdown (dashed). The curves for sols 58, 61, 76, and 193 were obtained with the right eye, sol 69 with the left eye, and sol 64 with each eye (right eye dashed). From sol 64, there were times with the helicopter out of the field of view that were not measured.
Friction velocity and helicopter altitude. The Rabinovitch et al. (2021) model, adapted for atmospheric density of 0.020 kg/m3, 2,800 rpm, and Thrust:Weight = 1, is shown as a red dashed line. Horizontal lines show representative thresholds for a conventional model (Shao & Lu, 2000) and a low-pressure model (Swann et al., 2020); the calculated thresholds are for mobilization of sand (200 diameter, 3,200) and aggregates (500 μm, 380 kg/m3). Vertical solid lines show representative altitudes at which dust lifting was seen during landing and traverse; dotted lines are extended upward to 2x the model prediction.
