Radius of giant planets as a function of mass for different moments in time. The lines correspond from top to bottom to t = 0.1 (magenta, long-dashed), 1 (blue, dashed-dotted), 4.6 (red, solid), and 10 Gyr (green, short-dashed). All planets are at 5.2 AU from the sun and have a core of 33 M_⊕, except for the 0.14 M_X planet, which has a core of about 18 M_⊕. The two dotted, very light blue lines show the result from Fortney et al. (2007) for planets with cores equal to 25 M_⊕ at 1 AU (upper line) and at 9.5 AU (lower line), at 4.5 Gyr. The dotted branch of the magenta line in the top right corner shows the result for “hot start (accreting)” simulations. Otherwise, the radii are virtually identical for the “hot” and “cold start” scenario at these late times.