DIVerse Exoplanet Redox State Estimations

New observational capabilities with the JWST and ARIEL space telescopes will strongly advance our ability to characterize exoplanetary atmospheres. While the community focusses mainly on biosignatures, in DIVERSE I will search for signatures of geophysical factors that influence habitability, specifically the diversity of planetary redox states. The redox state is of major importance for habitability, since reducing conditions favour prebiotic chemistry for life as we know it. Atmospheres of rocky planets are typically divided into two distinct classes – H2/He-dominated (reduced) atmospheres of primordial origin – here denoted as Class I planets – or secondary (more oxidized) atmospheres of volcanic origin – here named Class II planets. In the Solar System, observations are limited to old, evolved atmospheres that became oxidized over time and do not allow to directly constrain the planets’ interior redox states. Furthermore, detection of reduced species such as CO or CH4 does not unambiguously link back to the interior redox state.In contrast, if we were able to detect H2-dominated atmospheres lacking He – here called Class X planets – the most likely explanation would be strongly reduced degassing from the magma ocean or subsequent volcanism. Distinguishing Class I and X planets would truly allow to constrain the planetary redox state and indicate how it depends on observables such as stellar composition or planetary mass. Estimates on the distribution and observability of Class X planets are yet missing but became recently possible. DIVERSE will build strong predictive, theoretical models, linking the interior evolution including core formation with atmospheric abundance and erosion models including the observability potential, to determine the diverse evolution pathways of reducing atmospheres of primary, secondary or hybrid origin. I will thus address whether (and for which planet classes) the atmosphere could indeed serve as a window into the interior.