Observing Exoplanet Biosignatures outside the Conservative Habitable Zone

Abstract Liquid water can exist on exoplanets in a circumstellar region significantly wider than the Conservative Habitable Zone (CHZ). In particular, tidally locked planets orbiting closer inwards than the inner CHZ border could have liquid water on their night side provided the heat transport between the day and night side is low. Planets further away than the outer CHZ boundary can maintain subglacial liquid water if they have geothermal heat sources or in the form of subglacial lakes similar to the Martian polar lakes. Pressurized water can reach the planetary surface through faults and cracks in the ice cover, creating plumes and enriching the atmosphere with molecules that may be present in subglacial oceans. We discuss the model and the conditions needed to detect water and other molecules in the transmission spectrum by JWST, as have recently been detected in small hot exoplanets such as GJ287 b.