Energy-limited escape flux as a function of stellar age (ϵ = 0.15; solid curve) for Gl 581 c (black) and HD 85512 b (gray). The dotted curve is the diffusion limit in the runaway state (f_str(H₂) = 0.1 and T_str = 300  K), and the dashed curve is an upper limit to the escape in the collapse state (f_str(H₂) = 10^-4 and T_str = 220  K). The time needed to evaporate an Earth ocean of water (≈ 1.4 × 10²¹ kg) is indicated on the right scale.