Penetrating Solar Wind Protons in Venusian Upper Atmosphere Based on Venus Express Observations

A fraction of solar wind protons can be neutralized by the charge exchange process before they encounter the Venusian bow shock, allowing them to penetrate the dayside induced magnetosphere as neutral solar wind hydrogen atoms. These hydrogen atoms precipitate onto the Venusian upper atmosphere and are partially re‐ionized to become penetrating solar wind protons, providing insights into both solar wind dynamics and the Venusian exosphere. We utilized Venus Express Ion Mass Analyzer data to identify the signatures of penetrating solar wind protons. We systematically surveyed the proton data to provide statistical evidence for the presence of penetrating solar wind protons in the Venusian upper atmosphere, with an average flux of 4.4 10 3 cm −2 s −1 . From this flux, we derive the upstream column density of the Venusian exosphere to be ∼10 10 cm −2 , which is consistent with values obtained from previous Venusian exosphere observations and models. We also discuss the significance of penetrating solar wind protons by comparing them with the case of Mars.