  A free-floating planet is a planetary-mass object that orbits around a
non-stellar massive object (e.g. a brown dwarf) or around the Galactic Center.
The presence of exomoons orbiting free-floating planets has been theoretically
predicted by several models. Under specific conditions, these moons are able to
retain an atmosphere capable of ensuring the long-term thermal stability of
liquid water on their surface. We model this environment with a one-dimensional
radiative-convective code coupled to a gas-phase chemical network including
cosmic rays and ion-neutral reactions. We find that, under specific conditions
and assuming stable orbital parameters over time, liquid water can be formed on
the surface of the exomoon. The final amount of water for an Earth-mass
exomonoon is smaller than the amount of water in Earth oceans, but enough to
host the potential development of primordial life. The chemical equilibrium
time-scale is controlled by cosmic rays, the main ionization driver in our
model of the exomoon atmosphere.
