EFFECTS OF THE CORE COOLING ON THE INTERNAL DYNAMICS AND THERMAL EVOLUTION OF TERRESTRIAL PLANETS

The effects of thermal coupling of the core and mantle on the thermal evolution and mantle dynamics of terrestrial planets are investigated using three-dimensional thermal convection models in a spherical shell . Three pairs of models are presented to study mantle models of differ ent viscosities and internal heating. In each pair, one model adopts a constant temperature at the core-mantle boundary, and the other allow s the core to thermally couple to the mantle and cool. In the first an d second pairs, the mantle is heated only from below, whereas in the t hird pair, internal heating is due to radioactive elements. The mantle viscosity of the first and third pairs is 10(21) is, while the mantle of the second pair has a viscosity of 10(22) Pa s. The thermal coupli ng of the core and mantle has strong effects on the thermal boundary l ayer near the core-mantle boundary but only minor effects on the therm al boundary layer near the surface. It cools the core, substantially w eakens the thermal boundary layer near the core-mantle boundary, and t hus reduces the vigor of convection in the mantle. The models with coo ling cores result in a substantially colder and relatively less dynami c mantle than the models with a fixed temperature at the core-mantle b oundary which overestimates temperatures in the mantle.