Implications of an internal dynamo for the thermal history of Mercury

Constraints placed on the thermal evolution of Mercury by the dynamo model of the planet's magnetic field are investigated. It is assumed that Mercury is a differentiated planet possessing an iron-nickel core with a radius approximately three-fourths of the planetary radius, that the mantle is made of silicates with thermal and rheological properties similar to those of earth's upper mantle, and that differentiation was a global process which resulted in the removal of radioactive heat sources from the core and the upward segregation of heat sources in the mantle. These assumptions are found to lead to the conclusion that the existence of a molten core requires the retention of a minimum concentration of heat sources throughout the mantle, the value being comparable to the mantle-wide average concentration for earth. Thus, it is suggested that the differentiation of Mercury could not have resulted in the complete removal of heat sources from the mantle into a crust near the planet's surface.