Radius anomaly (difference between observed and modeled radius – see text –) as a function of planetary mass (in log) for a selection of known transiting giant planets. Left panel: standard models (including stellar irradiation but no extra heat source) are used for the comparison. Right panel: models assume an extra heat source at the planet’s center equivalent to 1% of the incoming stellar heat flux (see Guillot & Showman 2002). CoRoT-2b is labeled “27”. It is the most anomalously large planet on the right panel.