Electrostatic Repulsion of Dust from Planetary Surfaces

Abstract

Surfaces of planetary bodies can have strong electric fields, subjecting conductive grains to repulsive electrostatic forces. This has been proposed as a mechanism to eject grains from the ground. To quantify this process, we study millimeter-sized basalt aggregates consisting of micrometer constituents exposed to an electric field in drop-tower experiments. The dust aggregates acquire high charges on subsecond timescales while sticking to the electrodes according to the field polarity. Charging at the electrodes results in a repulsive (lifting) force and continues until repulsion overcomes adhesion and particles are lifted, moving toward the opposite electrode. Some aggregates remain attached, which is consistent with a maximum charge limit being reached, providing an electrostatic force too small to counteract adhesion. All observations are in agreement with a model of moderately conductive grains with a small but varying number of adhesive contacts to the electrodes. This supports the idea that on planetary surfaces with atmospheres, electrostatic repulsion can significantly contribute to airborne dust and sand, i.e., decrease the threshold wind speed that is required for saltation and increase the particle flux as suggested before.

Charged Atmospheric Aerosols from Charged Saltating Dust Aggregates

“…We connect this work to the one by Onyeagusi et al [17]; while the previous work looked into the charging behavior of dust aggregates on a conductive surface within an electric field, we now study the charge exchange during the collision of two such aggregates. We focus on the charge balance of these collisions.…”

“…Due to the weak contrast and crowded field of view, the small grains we observe cannot always be attributed to a specific collision of larger aggregates. However, according to Onyeagusi et al [17], charged grains of pixel size will be accelerated by and eventually stick to one of the electrodes and cannot be ejected or released through recharging. Therefore, we assume that the fine dust that moves freely through the chamber is a result of aggregate collisions and we conclude that its charge is not influenced by recharging at the electrodes.…”

“…As a matter of fact, Esposito et al [16] found that these electric fields can strongly increase the amount of material lifted. Onyeagusi et al [17] studied this additional lifting force in an electric field on an individual grain level in drop tower experiments. They showed that basalt dust aggregates, adhering to a conductive surface in a strong electric field charge until the repulsive force is strong enough to outweigh adhesion.…”