Redox Disequilibrium in the Clouds of Venus – A Sign of Life

The simultaneous occurrence of highly oxidised and highly reduced molecules in an atmosphere, such as O2 and CH4, is known to be caused by biological activity on Earth. Therefore, such Redox Disequilibrium Pairs (RDPs) have been suggested as spectral signatures for the detection of life on other planets. On Venus, such RDPs have indeed been detected in form of H2S, NH3 and PH3 in combination with O2, leading to the hypothesis that some microbiological activity might be sustained in the liquid droplets forming the clouds on Venus. Our project will investigate whether other abiotic reaction pathways can create RDPs on Venus, both theoretically and experimentally. We will carry out novel laboratory experiments of UV photo-processes on acidic surfaces, and apply the measured rates to the sulphuric acid cloud particles in the Venusian clouds irradiated by the Sun. We will include these processes into our advanced chemical models for the whole Venus atmosphere reaching from the hot rocky surface at 90bars to high above the clouds, where the pressure drops to micro-bars. These models include the outgassing and deposition at the interface of the atmosphere to the rocky ground, gas-kinetic and photo-chemical processes, diffusive mixing, radiative transfer, and the formation of sulphuric acid cloud particles and the chemical processes occurring at their surfaces. In addition, we will perform new evolutionary models for Venus to study whether Venus might have had an ocean in its history, providing the habitable conditions in its past necessary to develop the life forms that might still be present in the clouds today, and how the water disappeared via atmospheric escape. The upcoming Venus exploration missions, in particular the ESA EnVision mission, but also DaVinci and the Life Finder mission, will provide excellent and timely opportunities to check and verify our conclusions.