Effect of a thermally stratified layer in the outer core of Mercury on its internally generated magnetic field

The low intensity and lack of small-scale variations in Mercury’s present-day magnetic field can be explained by a thermally stratified layer blanketing the convective liquid outer core. The presence of a present-day stable layer is supported by thermal evolution studies that show that a sub-adiabatic heat flow at the core-mantle boundary can occur during a significant fraction of Mercury’s history. The requirements for both the likely long-lived Mercury dynamo and the presence of a stable layer place important constraints on the interior structure and evolution of the core and planet.

We couple mantle and core thermal evolution to investigate the necessary conditions for a long-lived and present-day dynamo inside Mercury’s core by taking into account an evolving stable layer overlying the convecting outer core. Events such as the cessation of convection in the mantle may strongly influence the core-mantle boundary heat flow and affect the thickness of the thermally stratified layer in the core, highlight the importance of coupling mantle evolution with that of the core. We employ interior structure models that agree with geodesy observations and make use of recent equations of state to describe the thermodynamic properties of Mercury’s Fe-S-Si core for our thermal evolution calculations.