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C.E. Krauss, M. Horanyi (LASP, Univ. of Colorado), S. Robertson (Dept. of Physics, Univ. of Colorado)
Due to the prevalence of Martian dust devils and dust storms, an understanding of the underlying physics of electrical discharges in Martian dust is critical to future Mars exploratory missions. When dust particles come into contact, charge can be transferred between the grains. Wind driven dust studies by Stow (Weather, 1969) show that in the case of particles with identical compositions, the particle with the larger radius in a collision preferentially becomes positively charged. The stratification of particle sizes generated by upwinds within a dust cloud causes an electric dipole to form. When the electric potential within the cloud exceeds the breakdown voltage of the surrounding atmosphere, a discharge occurs.
Mars' low atmospheric pressure and arid, windy environment suggest that the dust near the surface of Mars is even more susceptible to triboelectric charging than terrestrial dust. Electrical discharges on Mars should occur more frequently but at lower intensities than those seen on Earth.
We have conducted experiments to determine the range of pressures and wind speeds over which discharges can be observed. We have also investigated the affects of regolith particle size on the discharges. Measurements done in our lab on the charging of single dust grains show that particles of JSC-Mars-1, a Martian regolith simulant, can have large electrical potentials due to triboelectric charging. When JSC-Mars-1 is agitated in a low-pressure CO2 atmosphere, electrical discharges are electronically detected. Under extremely dark viewing conditions, these electrical discharges are visually observed in the laboratory at pressures between 0.1 and 50 Torr. Measurements of the frequency and intensity of these discharges as a function of pressure (from 0.5 to 7.3 Torr) and stirring speed (corresponding to wind speeds from 0.1 to 5 m/sec) show that discharges occur at pressures and wind speeds similar to those expected on the Martian surface.
This work is supported by NASA Space Science GSRP, NGT5-50345.