3D simulations of TRAPPIST-1e with varied incident UV produce degenerate O3 transmission spectra features

TRAPPIST-1e is a potentially habitable terrestrial exoplanet orbiting an ultra-cool M Dwarf star and a key target for observations with JWST. One-dimensional photochemical modelling of terrestrial planetary atmospheres has shown the importance of the incoming stellar UV flux in modulating the concentration of chemical species, such as O₃ and H₂O. Three-dimensional (3D) modelling has demonstrated anisotropy in chemical abundances due to transport in tidally locked exoplanet simulations. We use WACCM6, a 3D Earth System Model, to investigate how uncertainties in the incident UV flux, combined with transport, affect observational predictions for TRAPPIST-1e, assuming an initial Earth-like atmospheric composition. We use two semi-empirical stellar spectra for TRAPPIST-1 from the literature. The photochemically produced total O₃ columns differ by a factor of 24 between the simulations, with the depth of O₃ spectral features in transmission spectra leading to degenerate states (e.g. overlap with scenarios that assume alternative O₂ concentrations) when interpreting the observations. Without the direct detection of O₂, additional context for determining the oxygenation state of the atmosphere may be gained from future missions that can better characterise the UV spectra of faint stars, or sensitive multi-wavelength observations that span the visible and infrared regions.