Martian Atmospheric Electricity and Global Circuit Driven By Dust Storms

It is well-known that small particles of differing composition and size will exchange charge via contact electrification or "tribo-electrification". On Earth, mixing grains in dust devils have been found to generate electricity via tribo-electric processes. When in collision with the ground or surface, smaller grains tend to obtain a negative charge polarity while heavy grains/surface contain an equal and opposite positive charge. Due to vertical winds, the small negative grains are lofted high into the storm thereby generating a charge separation into a dipole and thus creating macroscopic electric dipole moment within the storm. Electric fields in terrestrial dust devils have been measured to exceed 100 kV/m in a coherent, dipolar configuration that is consistent with a dipole moment oriented downward (negative charge at higher altitudes). It is believed that similar processes occur in Martian dust devils and storms, giving rise to large dust storm E-fields. Since electrical breakdown in CO2 gas is ~ 20 kV/m, the storm E-fields are limited in values to levels well below that of terrestrial dust devils/storms. However, the low levels of electrostatic energy density are compensated by the relatively large volumes of the storms that can then create a global atmospheric electric circuit. Previous analysis suggest the circuit is highly variable, becoming most intense during dust storm season. The storms may also modify atmospheric chemistry, creating oxidants and becoming a sink for atmospheric methane. We will review models of the Martian dust storm electrostatic system, global circuit, and introduce the new harsh chemistry that can occur. We will also show lab and desert studies that are consistent with these models.