Evolution of the KOI-1257b radius as a function of the age. The 68.3%, 95.5%, and 99.7% confidence regions are denoted by black, dark grey, and light grey areas, respectively. The curves represent the thermal evolution of a 1.45 M_♃   planet with a time-averaged equilibrium temperature of 511 K. Text labels indicate the amount of heavy elements in the planet (its core mass, in Earth masses). No dissipation of incoming stellar flux was considered (standard models), as they do not significantly depart from the ones shown above.