Radius vs. age for the planet HD 209458b. The solid red lines are for MESA, using the gray_irradiated atmosphere model. The dotted black lines show the CEPAM code results. The dashed blue lines show the MESA calculation using the F –Σ surface heat source. The data point with error bars is the observed value of the radius for HD 209458b quoted in Guillot (2010). The two sets of curves are deep heating (upper three curves) and shallow heating (lower three curves).