The Importance of Pickup H ⁺ Escape at Mars

Abstract The loss of hydrogen ions on Mars to space largely occurs through the interaction of solar wind with planetary atmosphere. However, the relative importance of different ion escape channels is not yet fully understood. In addition, there are still open questions about the proportion of escape in relation to total hydrogen loss. Using magnetohydrodynamics (MHD) modeling, we demonstrate that the dominant pathway for planetary loss is not the ionospheric ion outflow through the magnetotail, but rather the pickup ion escape of newborn generated by solar wind charge exchange with Mars' extended hydrogen exosphere. We further show that the seasonally recurring or dust storm‐driven variations in hydrogen exosphere density can modulate the escape rate. The dependence of modeled escape rate on solar wind flux highlights the importance of the pickup ion escape channel for hydrogen loss in the history of Mars.