Three-dimensional simulations of thermal and non-thermal hydrogen and deuterium escape from Venus

The enrichment of Venusian atmospheric D/H ratio is commonly interpreted as evidence for substantial water loss, but its connection to present-day atmospheric escape remains uncertain. Because hydrogen and deuterium can escape through different thermal and non-thermal pathways, quantifying their relative escape rates is essential for assessing the escape fractionation of Venusian water. We present new developments of the LMDZ Venus Planetary Climate Model for the study of H and D escape. Building on the recent thermospheric and ionospheric extension of the model, we have introduced deuterium-bearing species and reactions, allowing the H- and D-bearing species to be followed from the lower atmosphere to the thermosphere. The model is used to compute the thermal escape of H and D and to provide a self-consistent three-dimensional atmospheric and ionospheric background for non-thermal escape calculations. Photochemical escape is investigated with a Monte Carlo test-particle model, while solar-wind-driven ion escape is studied by coupling the Venus PCM outputs to the LatHyS Venus hybrid model. This work provides a unified framework for comparing the main escape channels of H and D at Venus and for estimating the present-day D/H escape fractionation factor. It offers a step toward linking current upper-atmospheric loss processes to the long-term isotopic evolution history of Venusian water.