Different mechanisms of moon loss as a function of the system’s parameters. The top panel shows the instability limit (a_m = 0.36 r_H) for a Super Earth-like and Jupiter-like planet in solid lines, and the midpoint radius r_M (evaluated with the planet spinning at 2/3 its maximal rate) in dashed lines. The second panel shows the regions of parameter space for the lunar mass ratio (m_m/m_p) and planet semi-major axis (a_p) for a typical super Earth (SE). The gray region above the black dashed line is where moons are lost anyway through runaway migration (Barnes & O’Brien 2002). The vertical green line denotes the boundary between where planets do and do not despin within ∼1 Gyr (Eq. (10)). The blue solid curve denotes the boundary where lunar tidal migration (Eq. (29)) and tidal planet despinning result in comparable changes to a_m/r_M (Eq. (34)): above this curve, E₁ is crossed due to lunar migration; below this curve, E₁ is crossed due to planetary despinning. The blue dashed line denotes the boundary where lunar tidal migration results in significant changes to a_m/r_M in ∼ Gyr timescales. Accordingly, the region where moons are lost due to lunar migration (with or without capture in secular spin–orbit resonance) is shaded blue, and the region where moons are lost due to planetary despinning is shaded green. The vertical purple line denotes the point at which r_M = 5R_p (Eq. (33)). The middle panel is the same for the parameters of Kepler-79d, and the red cross denotes the fiducial parameters adopted for a hypothetical moon (see Fig. 6). The bottom panel is the same for a Jupiter-mass planet.