Irradiation temperature T_irr as a function of the planet’s temperature T_p. Several curves are obtained due to different values of g_b and M_b in the available parameter range. The coldest planets exhibit a degeneracy, as the same amount of irradiation is consistent with two different atmospheric structures. As shown by the color bar, when taking the “hot” solution for T_p, the temperature at the bottom of the atmosphere T_b is >2000 K.