Mars' atmosphere, volatiles, and climate as the sun heats up over the next 6 billion years

As the solar luminosity continues to increase over the next 6 billion years, the Martian surface will heat up to above the melting temperature of water ice. Water ice currently in the polar caps and ground ice will melt, potentially repopulating crater lakes or a very small ocean, with the abundance possibly enhanced due to diffusion upward of water currently locked in the deep crust. CO2 adsorbed in the regolith and locked up in the south-polar ice cap will diffuse into the atmosphere, providing up to 50 mbar total pressure; this will further increase the temperature via greenhouse warming. There are two end-member scenarios for the climate under these conditions: (i) Surface water could drive an atmospheric water cycle somewhat analogous to present-day Earth's, which would create a global clement climate conducive to the existence of widespread surface life. (ii) The widespread presence of liquid water could cause CO2 to form carbonate minerals and H2O to hydrate surface/subsurface minerals (or allow H released from water to escape to space), and CO2 and H2O could be lost to space, leaving Mars with a dry environment. The climate could end up between these end-members and also could vary with time. This uncertain climate end state informs our view that exoplanet evolution and habitability can be driven by endogenous processes associated with a terrestrial planet as well as by the ability of EUV and a stellar wind from the host star to strip away atmosphere.