The Influence of Solar Irradiation and Solar Wind Conditions on Heavy Ion Escape from Venus

We apply a recently proposed method to estimate heavy ion (O+) escape from Venus, combining in situ spacecraft observations from Venus Express (VEX) with a hybrid plasma model that treats ions as particles and electrons as a fluid. Using this approach, we examine how various upstream solar conditions—including extreme ultraviolet (EUV) radiation, solar wind dynamic pressure, and the strength and cone angle of the interplanetary magnetic field (IMF)—influence heavy ion loss. Our results show that the heavy ion escape rate exhibits no clear dependence on EUV radiation, possibly due to transport-limited processes. Under low EUV conditions, the escape rate increases with solar wind dynamic pressure, whereas no consistent trend is observed under high EUV. The escape rate decreases with increasing IMF strength and is highest when the solar wind flow is aligned with the IMF (i.e., small cone angle), and lowest when the flow and field are perpendicular. In general, some of these findings agree with what has previously been found for Mars, but Venus appears to be less sensitive to solar variability than Mars.