Nighttime ionosphere caused by meteoroid ablation and solar wind electron-proton-hydrogen impact on Mars: MEX observation and modeling

Abstract

We report that radio science (RS) experiment onboard Mars Express (MEX) has observed three plasma layers in the nighttime ionosphere of Mars at altitudes ~80–100 km, ~120 km, and ~160 km, which are reproduced by model calculation due to impact of meteoroid, solar wind proton, and electron, respectively. The densities of 21 ions (Mg⁺, Fe⁺, Si⁺, MgO⁺, MgCO₂⁺, MgO₂⁺, MgN₂⁺, FeO⁺, FeO₂⁺, FeN₂⁺, FeCO₂⁺, SiO⁺, SiCO₂⁺, SiN₂⁺, SiO₂⁺, CO₂⁺, N₂⁺, O⁺, O₂⁺, CO⁺, and NO⁺) have been computed between altitude 50 km and 200 km. The model shows that all atmospheric ions (CO₂⁺, N₂⁺, O⁺, CO⁺, O₂⁺, and NO⁺) are produced above 100 km due to solar wind electron and proton impact ionizations. The metallic ions are formed between 50 km and 100 km due to ablation of micrometeoroids. It is found that mass ~3.0 × 10⁻⁴ g of incoming meteoroid is sufficient for meteor ablation and its characteristic flux ~4.0 × 10⁻¹⁵ cm⁻²s⁻¹ could produce the nighttime metallic layer observed by MEX. The calculated electron densities are also compared with the occultation measurements made by Mars 4/5 in the nighttime ionosphere of Mars.