Plot of the E₁ region for two different values of a_m/R_p. For a planet born rapidly rotating, no moon will be found in the shaded regions of parameter space, as otherwise passage through the E₁ region during the planet’s tidal despinning and alignment occurs. The E₁ region can also be encountered due to lunar migration if the lunar migration timescale is faster than the planet’s despinning timescale. In this case, the moon is lost if the planet’s obliquity lies within about 69^◦ and 111^◦ (i.e. between the black dashed lines) independent of a_m/R_p.