Logarithm of the mass-loss rates (colour coded) as a function of planetary mass and radius. The adopted T_eq and F_XUV values are given on the top of each panel. The equilibrium temperature increases from top to bottom, while F_XUV increases from left to right. All planets orbit a 1.0 M_⊙ star. For reference, the dashed lines mark constant Λ values of 8, 20, and 50 (from top to bottom). The red lines indicate planets for which the Knudsen number at the upper boundary is equal to one (solid line) and ten (dashed line).