Probing Venus’ Extended Exosphere through Deuterium and Hydrogen generated Pick-Up Ion Cyclotron Waves

Despite decades of exploration by multiple space missions, the history of water on Venus remains uncertain, limiting our understanding of the planet’s evolution and its potential for habitability. The atmospheric deuterium-to-hydrogen (D/H) ratio is a key tracer of past water loss and atmospheric escape processes. To date, measurements of this ratio have been largely confined to altitudes at or below the exobase level, derived from remote sensing and in situ observations of water vapor. In this work, we revisit magnetic field observations from Venus Express to analyze pick-up ion cyclotron waves generated by freshly ionized hydrogen, so called proton cyclotron waves (PCWs). We further extend this approach to investigate pick-up ion cyclotron waves associated with deuterium ion pick-up, providing the first altitude-resolved density profile of deuterium in Venus’ extended exosphere. We find that the hydrogen escape rate is consistent with previous observations, while the inferred deuterium escape rates are higher than expected, indicating a limited Venusian water inventory with implications for the planet’s atmospheric and planetary evolution (see EGU Abstract from Scherf+).