Atmospheric chemistry of a free-floating planet's exomoon

A free-floating planet (FFP) is a planetary-mass object that does not orbit a star but orbits a galactic center directly or a non-star massive object (like a brown dwarf or other FFP). It has been suggested that a FFP might conserve its companion moon in the ejection from a forming planetary system. The existence of life on a FFP's moon depends on the capability to reach (in the absence of a companion star) a temperature that allows relevant processes for life to take place. With a considerable atmosphere, this may ensure the long-term thermal stability of liquid water on the surface of that body. We employ the one-dimensional radiative-convective code PATMO to model the thermal structure of planetary atmospheres, coupled to gas-phase chemical kinetics. Opacity plays an important role in the thermal profile of an atmosphere. In this specific case, we employ a frequency averaged gray opacity function. We consider cosmic rays chemistry and molecular/eddy diffusion, and include tidal and radiogenic heating. Our ultimate goal is to assess the conditions under which liquid water might exist on the surface of such a moon. We explore different initial conditions and find that liquid water could exist if we consider that orbital parameters can be stable over time. The chemical evolution in a low-temperature environment can be slow, but it is plausible. The next step in our investigation is to further analyze the time evolution of water formation and include the rain-out process, which is important to estimate the amount of water.