Modelling Wind-Driven Ionospheric Dynamo Currents at Mars: Expectations for InSight Magnetic Field Measurements

We model expected dynamo currents above, and resulting magnetic field profiles at, InSight's landing site on Mars, including for the first time the effect of electron-ion collisions. We calculate their diurnal and seasonal variability using inputs from global models of the Martian thermosphere, ionosphere, and magnetosphere. Modeled currents primarily depend on plasma densities and the strength of the neutral wind component perpendicular to the combined crustal and draped magnetic fields that thread the ionosphere. Negligible at night, currents are the strongest in the late morning and near solstices due to stronger winds and near perihelion due to both stronger winds and higher plasma densities from solar EUV photoionization. Resulting surface magnetic fields of tens of nanotesla and occasionally >100 nT may be expected at the InSight landing site. We expect currents and surface fields to vary significantly with changes in the draped magnetic field caused by Mars' dynamic solar wind environment. Plain Language Summary In the upper atmospheres of planets, solar extreme ultraviolet (EUV) radiation produces ions and electrons. Electric currents flow whenever electrons and ions move differently from each other, due to their opposite charges and different masses. When neutral wind causes this differential motion, it is called a dynamo current. Here we simulate these dynamo currents above the NASA InSight Mars lander, resulting from magnetic and collision forces acting upon ions and electrons in the Martian upper atmosphere. We find that modeled currents primarily depend on (a) the density of electrons and ions and (b) the strength of the neutral wind component that is perpendicular to the combined draped and crustal magnetic field that sits within the Mars ionosphere. Negligible at night, predicted currents are the strongest in the late morning and near solstices, due to stronger winds, and near Mars' closest approach the sun, due to both stronger winds and higher plasma densities from solar EUV photoionization. Resulting surface magnetic fields of tens of nanotesla and occasionally >100 nT may be expected at the landing site. We expect currents and surface fields to vary significantly with changes in the draped magnetic field caused by Mars' dynamic solar wind and space weather environment.