The Three-Dimensional Structure of the Martian Ionosphere from MAVEN Observations

Abstract:

To the first order approximation, the structure of the induced Martian magnetosphere during solar maximum can be considered in terms of pressure balance, where pressure in the solar wind (dominated by dynamic pressure) is ultimately balanced by pressure in the ionosphere (dominated by thermal pressure). During solar minimum, by contrast, the ionospheric pressure may be insufficient to balance the pressure from the solar wind. Each ion species, as well as electrons, contribute to thermal pressure, and the distribution and temperature of each species can vary spatially and temporally. Carried by the Mars Atmospheric and Volatile EvolutioN (MAVEN) spacecraft, the Neutral Gas and Ion Mass Spectrometer (NGIMS) has been providing measurements of ionospheric species below ~500 km altitude since October 2014. We present statistical analyses of NGIMS ion observations in order to determine the three dimensional morphology and variability of the ionosphere and the ion contribution to ionospheric thermal pressure. The spatial and temporal variability of the main ionospheric species (O⁺, O₂⁺, CO₂⁺) are mapped in three different coordinate systems: geographic, Mars-solar orbital, and Mars-solar electric field. Maps of ion thermal pressure are produced, with special attention to dependence on solar EUV flux, asymmetries with respect to the solar wind convection electric field, and non-uniformity associated with crustal magnetic fields.