Contours of maximum stellar masses (abscissa) for two possibly habitable moons with given planetary host masses (ordinate). Solid lines correspond to the satellite’s time lag τ_s of 638 s and one out of five eccentricities, namely those of Io, Callisto, Europa, Titan, and 0.05, from left to right. Dashed lines refer to e_ps = 0.05 and variation of τ_s by a factor of ten. A satellite with host star and host planet masses located left to its respective eccentricity contour is uninhabitable.