Thermal and magnetic evolution of Mercury with a layered Fe-Si(-S) core
Christopher J. Davies, Anne Pommier, Sam Greenwood, Alfred J. Wilson
Abstract
Elucidating the structure and composition of Mercury is important for understanding its interior dynamics and evolution. The planet is characterised by unusual chemical characteristics and a weak magnetic field generated in a large metallic core, and its early evolution was also marked by the presence of a magnetic field, widespread volcanism and global contraction. Here we develop a parameterised model of coupled core-mantle thermal and magnetic evolution considering a layered Fe-Si(-S) core structure with chemical and physical properties of the mantle and the core based on previous laboratory studies. We seek successful solutions that are consistent with observations of Mercury's long-lived dynamo, total global contraction, present-day crustal thickness, and present-day interior structure. Successful solutions have a mantle reference viscosity > 10 21 Pa s (corresponding to a present-day bulk mantle viscosity > 2 × 10 20 Pa s), a silicon concentration in the core >13 wt%, a present inner core radius of ∼ 1000 − 1200 km and a thermally stable layer ∼ 500 − 800 km thick below the core-mantle boundary. Our results show that if present, a molten FeS layer atop the core has minimal effect on Mercury's long-term thermal and magnetic evolution. Predictions from our models can be tested with upcoming Bepi-Colombo observations. • We model core-mantle thermal-magnetic evolution of Mercury with an Fe-Si-S core. • We seek models matching Mercury's dynamo activity, contraction and crustal thickness. • Viable models have > 13 wt% core Si, a ∼1100 km inner core and ∼700 km stable layer. • A molten FeS layer atop the core has minimal effect on Mercury's evolution.