Effects of basin-forming impacts on the historical Martian dynamo

It is now well accepted that Mars had an active dynamo in its early history [1-2], evidenced by the strong remanent crustal field observed by Mars Global Surveyor [3]. Recent studies [4] show a strong correlation between the timing of the dynamo termination and giant impacts (forming basins greater than 1000 km in diameter) during the mid-Noachian period. Further modeling studies [5-9] suggest that such impacts could generate a strong thermal heterogeneity in the deep interior. These results imply that giant impacts may play an important role in terminating the Martian dynamo via several possibilities, e.g., a small perturbation ending permanently a subcritical dynamo, or a strong thermal heterogeneity destroying a supercritical dynamo. To better understand the effects of basin-forming impacts on Martian dynamo, we simulate the Martian dynamo with a heterogeneous heat flux across the core mantle boundary arising from the shock heating from such impacts (e.g., Utopia). Our initial results show that depending on the location, the influence of the impacts can be catastrophic: a modest thermal heterogeneity from an impact in the equatorial region can destroy a strong field dynamo. However, if the same impact occurred near the polar region, the effect on the dynamo is minimal. These results could have implications on other geodynamic processes, e.g. paleo polar motion of Mars.