Thermal evolution and magnetism of terrestrial planets.

We evaluate a numerical model on the thermal evolution of terrestrial planets to estimate life-time of planetary intrinsic magnetic field for various mass planets. In this model, we take into account the pressure-dependency of density profile of the planet by using Birch-Murnaghun equation of state, and simulate thermal evolution of the planet by means of mixing length theory. According to our numerical results, the planetary mass must be between 0.1 and 1.4 Earth mass to sustain the intrinsic magnetic field for 4.5Gyr. If existence of intrinsic magnetic field were a key factor to make the planet habitable, the mass range above indicates that super-Earths would not be habitable.