Novel Experiments to Measure the Viscosity of MgO at Lower Mantle Conditions*

The viscosity of minerals such as magnesium oxide (MgO) under high pressures and temperatures strongly influences a terrestrial planet’s mantle dynamics, which dictates most of the planet’s chemical and thermal evolution. On Earth, mantle convection plays a crucial role in important processes like plate tectonics, volcanism, mountain building and magnetic field generation. Mantle dynamics also have a direct effect on the atmosphere and climate through interactions such as outgassing and the silicate-carbonate cycle. The mantle is expected to play a similarly important role in almost all other terrestrial planets. Characterizing mantle dynamics is crucial in our understanding of the geologic history of planets in our solar system, as well as establishing habitability of exoplanetary systems. Despite the importance of mantle material viscosity, there is currently no consensus from either theory or experiment on its value at high pressures (>50 GPa). The lack of constraint is often cited as a major source of uncertainty in planetary interior modeling, especially for super-Earths. We present initial results from two novel techniques that experimentally constrain the viscosity of MgO at high pressures and temperatures using laser compression along with the VISAR (Velocity Interferometer System for Any Reflector) and SOP (Streaked Optical Pyrometer) diagnostics.