The Impact of Background N₂ Pressure on the Habitability of Tidally Locked Rocky Exoplanets Around Cool Stars

Introduction: Rocky exoplanets in the habitable zones (HZ) of low mass stars will be prime targets for atmospheric characterization with the James Webb Space Telescope (JWST). Such planets are likely tidally locked and the determination of the habitability of those worlds requires the use of 3D global climate models (GCMs) to resolve the large-scale atmospheric circulation, heat transport, latitudinal and longitudinal water profiles and cloud coverage. Previous studies have determined the inner edge of the HZ for various low mass stars considering only a 1 bar background N₂ pressure. However, the background pressure can significantly impact the planet’s surface temperature, potentially enhance its habitability. Results: We show results from our GCM simulations using the Community Atmosphere Model 4 (CAM4), assuming a slab ocean configuration, for end member cases of low (0.25 and 0.5 bar) and high (10 bars) N₂ atmospheres. We compare our results of the inner edge of the HZ with Kopparapu et al., (2017), who assumed a 1 bar N₂ atmosphere. The assumed background pressure of N₂ has a meaningful effect on climate, stratospheric water vapor mixing, and deduced observables. Therefore, the inner edge of the habitable zone is sensitive the background gas pressure.