M‐GITM Simulations of the Ionosphere and Thermosphere of Mars During the 10 September 2017 Solar Flare Event: Changes Over Time During the Flare Event

Due to the rapid timescales of solar flares, the observed response of the upper atmosphere of Mars during a solar flare event depends on the timing within the flare event at which measurements are made. To accurately constrain the impact that solar flares may cause to the Martian upper atmosphere, the full time‐extent of a solar flare's atmospheric effects must as such be understood. In this paper, the full duration of changes to the Martian upper atmosphere due to the 10 September 2017 X8.2‐class solar flare are investigated using M‐GITM simulations. Analyses characterize the Martian upper atmosphere's electron, ion, and neutral densities and composition over time at the fixed location of MAVEN spacecraft periapsis observations during this flare event. In particular, the effects of the atmospheric processes that drive these changes—which are uniquely accessible during a solar flare's rapid changes due to their differing timescales—are investigated to provide insight into these time‐dependent changes. Results indicate rapid initial plasma density changes across the vertical extent of the ionosphere, plasma and neutral density changes with strong altitude‐ and species‐specific dependence, and a long duration of maximum perturbed upper atmospheric conditions due to this flare over time. The neutral thermosphere's thermal expansion over time is found to extend and magnify many of the density changes produced by photochemistry. Constraining solar flares' time‐dependent atmospheric effects provides context to future observation‐based comparisons of flare events and investigations into the role of solar irradiance in shaping Mars' early climate and impacting technology.