Structure and Sources for Mars' Night-side Ionosphere from MAVEN Observations

The Mars Atmosphere and Volatile Evolution (MAVEN) mission arrived in September 2014 and is the first to make comprehensive particle and field measurements down to altitudes of 150 km. This study focuses on the structure of Mars' night-side ionosphere, as defined by the densities of the dominant thermal ion species (O2+ and O+, measured by STATIC and NGIMS) and thermal electron densities (measured by LPW). We map these densities as a function of solar zenith angle, local solar time, altitude, latitude and longitude, and record additional information, including solar wind dynamic pressure (from SWIA measurements), magnetic field strength (from MAG), superthermal electron flux (from SWEA) and extreme ultraviolet flux (from EUV). At altitudes above 150 km, the night-side ionosphere is thought to be supplied by transport from the sunlit hemisphere (via bulk flow and plasma pressure gradients) and created in situ by precipitating particles (ions and electrons). These maps will help to identify the primary sources in specific regions of solar zenith angle, local time and altitude. For example, electron impact ionization is an important source for the night-side ionosphere, but access to specific regions is controlled by the magnetic field configuration. Night-side thermal plasma densities will be correlated with measured hot electron fluxes to investigate this relationship. We will also focus on the variation of thermal plasma density across the terminator as a function of altitude to investigate the role of bulk transport and plasma pressure gradients in supplying the night-side ionosphere.