Lifting of Tribocharged Grains by Martian Winds

TL;DR

This study demonstrates that tribocharging of sand grains can significantly lower the wind shear threshold needed to initiate sand transport on Mars, suggesting easier resumption of sand movement under Martian conditions.

Contribution

It provides experimental evidence and a model showing how surface electrification influences sand transport thresholds on Mars, a previously uncertain factor.

Findings

Electric charges reduce the threshold wind shear velocity for sand transport.

Tribocharging can facilitate the restart of sand movement after wind subsides.

Experimental results align with a model based on inhomogeneous surface charges.

Abstract

It is a long-standing open question whether electrification of wind-blown sand due to tribocharging - the generation of electric charges on the surface of sand grains by particle-particle collisions - could affect rates of sand transport occurrence on Mars substantially. While previous wind tunnel experiments and numerical simulations addressed how particle trajectories may be affected by external electric fields, the effect of sand electrification remains uncertain. Here we show, by means of wind tunnel simulations under air pressure of 20 mbar, that the presence of electric charges on the particle surface can reduce the minimal threshold wind shear velocity for the initiation of sand transport, u*ft, significantly. In our experiments, we considered different samples, a model system of glass beads as well as a Martian soil analog, and different scenarios of triboelectrification. Furthermore, we present a model to explain the values of u*ft obtained in the wind tunnel that is based on inhomogeneously distributed surface charges. Our results imply that particle transport that subsides, once the wind shear velocity has fallen below the threshold for sustained transport, can more easily be restarted on Mars than previously thought.