Titan

""Shit, they colonized one of the Saturn's moons." - Ratchet Paraforent, During reaction at hologram of moon Titan in underground base."

Titan is the largest moon of Saturn and the second-largest natural satellite in the Solar System. It is the only moon known to have a dense atmosphere, and the only known body in space, other than Earth, where clear evidence of stable bodies of surface liquid has been found. However, it was colonized by the Combine.