Observations and Modeling of the Mars Low-Altitude Ionospheric Response to the 10 September 2017 X-Class Solar Flare

Abstract : Solar extreme ultraviolet and X-ray photons are the main sources of ionization in the Martian ionosphere and can be enhanced significantly during a solar flare. On 10 September 2017, the Mars Atmosphere and Volatile EvolutioN orbiter observed an X8.2 solar flare, the largest it has encountered to date. Here we investigate the ionospheric response before, during, and after this event with the SuperThermal Electron Transport model. We find good agreement between modeled and measured photoelectron spectra. In addition, the high photoelectron fluxes during the flare provide adequate statistics to allow us to clearly and repeatedly identify the carbon Auger peak in the ionospheric photoelectron energy spectra at Mars for the first time. By applying photochemical equilibrium, O₂⁺ and CO₂⁺ densities are obtained and compared with Mars Atmosphere and Volatile EvolutioN observations. The variations in ion densities during this event due to the solar irradiance enhancement and the neutral atmosphere expansion are discussed.