Revival of surface water after the runaway greenhouse on close-in terrestrial planets

Close-in terrestrial planets orbiting M dwarfs can sustain ice cap on the permanent nightside under inefficient heat transport, which can bring potential habitability. However, the amount of ice may be limited considering the water surviving from the steam atmosphere after the runaway greenhouse state, and the condensation process through which water retains is not clear. Here, we use a two-column radiative-convective model to investigate the water condensation process of tidally locked planets after the runaway greenhouse state. We find that this process is determined by two equilibrium states, which results from the competition between the atmospheric greenhouse effect and dayside radiator fin. These equilibrium states are influenced by factors such as stellar flux and uncondensable greenhouse gases. Our result provides an easy method to quantify the amount of water condensed after runaway state and can help to understand water content of M dwarf planets.