Critical semi-major axes for Earth-like planets around low-mass stars. We show the results for an atmosphere with p_s = 1 bar (in blue) and p_s = 10 bar (in red). Planets on the right-hand side of the critical lines are expected to present asynchronous rotation. We also show the limits of the habitable zone (black curves) for stellar fluxes within 450 < F_* < 1508 W m⁻². The dots correspond to the already known planets (in black for R/R_⊕ < 1.7, in green for 1.7 < R/R_⊕ < 2.0, and in orange for 2.0 < R/R_⊕ < 2.2).