Ionospheric Effects of the X9.3 Solar Flare of 6 September 2017 on Earth and Mars: A Comparative Study of Density, Temperature, and Plasma Upflow

Abstract

Solar flares are known to strongly perturb the ionospheres of terrestrial planets through sudden enhancements in X-ray and extreme-ultraviolet (EUV) irradiance, yet relatively few studies have directly compared how this perturbation unfolds on different Earth-like bodies. Here we use two self-consistent, one-dimensional planetary ionosphere models to simulate how the Earth and Mars ionospheres responded to the solar flares of 6 September 2017. Both planets show a clear rise in electron density in the lower ionosphere, although the magnitude of this enhancement differs considerably between them. Ion-temperature responses are broadly similar at the two planets, with the background neutral atmosphere responsible for the differences that do appear. For the X9.3 flare, the electron temperature at Earth rises by as much as 250 K, whereas at Mars it instead falls by roughly 40 K. Both planets also develop an enhanced upward plasma velocity during the flare, and the resulting upward flux grows by 2.16 × 1012 m⁻² s⁻¹ at 800 km at Earth and by 8.45 × 109 m⁻² s⁻¹ at 400 km at Mars. To our knowledge, this is the first self-consistent simulation to reproduce a flare-driven enhancement of upward plasma flow at Mars.