Impact heating and coupled core cooling and mantle dynamics on Mars

Several giant impact basins of mid-Noachian age have been identified on Mars, and the global magnetic field appears to have vanished at about the same time. The impacts that formed these basins delivered a large amount of heat to the planetary interior, modified the pattern of mantle convection, and suppressed core cooling, potentially contributing to the cessation of dynamo activity. Here we investigate the thermal evolution of Mars in response to the largest basin-forming impacts, using a new method of coupling models of mantle convection with parameterized core cooling. We find that heating by a large impact generates a strong hemispheric upwelling in the mantle, which quickly spreads into a warm layer beneath the stagnant lid. The impact heating of the core leads to spherically symmetric stratification of the core; the outermost layers are strongly heated. This acts as a thermal blanket that prevents cooling of the interior and shuts down core convection. While the hottest part of the thermal blanket in the outermost core disappears relatively quickly, dynamo activity does not restart for similar to 100 Myr, and the core does not return to a fully convective state for similar to 1 Gyr following the impact.