Effects of Hot Oxygen Corona on Ion Escape From Venus‐Like Planets

Abstract

Due to the lack of a significant planetary magnetic field, the upper atmospheres of Venus‐like planets interact directly with the stellar wind. Therefore, thermal atomic oxygen in the thermosphere and hot oxygen in the corona produced by non‐thermal processes in the upper atmosphere act as a source of ion pickup loss. Here, we investigate the effects of hot oxygen corona on ion escape under different X‐ray and EUV (XUV) environments and stellar wind conditions. A Monte Carlo model is developed to simulate the transport of hot oxygen in the thermosphere. A simulation under present‐day Venus conditions successfully reproduces the observed oxygen density in the corona. The calculated hot oxygen distributions under different XUV environments are then used as input for a multispecies magnetohydrodynamic (MHD) model to simulate the stellar wind interaction with the upper atmosphere. The model results suggest that ion escape is controlled by flow patterns that depend on the pressure balance between ionospheric thermal and stellar wind dynamic pressures. This finding may account for the observed ion loss rate dependence on stellar wind dynamic pressure, as pointed out by previous studies on present‐day Mars and Venus. Under high XUV radiation, enhanced thermospheric heating causes the thermospheric component to dominate over the hot oxygen corona. Under low‐density stellar wind conditions, reduced stellar wind density suppresses ionization processes via charge exchange and electron impact ionization. Consequently, the contribution of hot oxygen corona to the total escape rate decreases under high XUV radiation or low‐density stellar wind.