[S-IT16] Planetary cores: Structure, formation, and evolution

[SIT16-05] Investigation of Mercury's Core using Electrical Laboratory Experiments and Parameterized Modeling

★Invited Papers

*Anne Pommier¹, Christopher Davies² (1.Carnegie Institution for Science, Earth and Planets Laboratory, Washington, DC, USA, 2.University of Leeds, School of Earth and Environment, Leeds, UK)

Keywords:Mercury's core, electrical and thermal conductivity, magnetic field, planetary cooling

Planet Mercury currently generates a weak intrinsic magnetic field that is thought to be generated by a convection-driven dynamo in the large metallic core. This field is related to the structure and cooling history of the planet, which remains to be elucidated. The electrical and thermal conductivities of relevant core analogs are fundamental physical properties to define the structure and evolution of the planet, and especially its possibly layered core. Constraining the electrical conductivity-depth profile of Mercury is a science objective of the ongoing ESA-JAXA Bepi-Colombo mission, because this physical property relates to the present-day thermal state and composition. The thermal conductivity of the core can be estimated from electrical conductivity values, and informs about the core state, its chemistry, and the magnetic field.
We present a joint experimental-modeling study of an Fe-Si-S Mercurian core. Electrical measurements have been performed in the multi-anvil press up to 15 GPa and 2000 K on Fe-S and Fe-Si alloys using impedance spectroscopy. Using previous electrical data on expected mantle analogs, an electrical profile within the planet is obtained. Electrical conductivity values are also used to estimate upper and lower bounds of thermal conductivity. These values are then implemented into parameterized mantle-core models of Mercury to investigate the magnetic field through time. We consider an Fe-Si core with the possibility of an FeS layer at the base of the mantle. Models are considered successful when they reproduce main observational constraints about the dynamo, present-day crustal thickness estimates, and the present-day global contraction of the planet. Our results show that if present, an FeS layer (up to 100 km thick) atop the core has minimum effect on the evolution of Mercury. We estimate a present inner core radius of ~ 1000 km and a thermally stable layer ~ 700 km thick.