Degassing history of Mars and the lifespan of its magnetic dynamo

[1] The volcanic and magnetic activity on the surface of Mars is directly related to its thermal evolution and to the melting potential of its mantle. Mars does not have an internal magnetic field today but geologic evidence suggests a dynamo was active during the first 500 to 800 million years of Martian history. The existence of the magnetic field on the planet sets a lower bound on the vigor of convection within its liquid core. The vigor of core convection can be maintained by efficient cooling of the overlying mantle. An initially wet mantle will promote strong convection, rapid core cooling, and dynamo activity. Magmatic degassing and planetary cooling increases the mantle's viscosity, thus decreasing the rate of core cooling and possibly terminating dynamo activity. The timescale for ending core dynamo activity is controlled by the initial amount of water in the mantle and by the efficiency of the degassing process. This process is an alternative to recent models that postulate dynamo termination on Mars is controlled by impact heating of the mantle.