Logarithm of tidal torque exerted on planet. In the cases of the pure solid (top panel) and oceanic (middle panel) tidal responses, and in the general case (bottom panel), these are shown as functions of the normalised semidiurnal frequency for a circularorbit (red line) and an orbit of eccentricity e = 0.2. The torques , , and are computed using the expression given by Eq. (44), and the values given by Table 1 for an Earth-sized planet orbiting TRAPPIST-1 (M_⋆ = 0.09 M_⊙) with a six-day orbital period. The Rayleigh drag frequency is set to σ_R = 1.0 × 10⁻⁶ s⁻¹. Solid (dashed) lines designate the regimes where the tidal torque drives the planet towards (away from) spin-orbit synchronousrotation.