Thermal Conductivity and Compressional Velocity of Methane at High Pressure: Insights Into Thermal Transport Properties of Icy Planet Interiors

Methane is a primary component of the “ice” layers in icy bodies whose thermal transport properties and velocity-density profiles are essential to understanding their unique geodynamic and physiochemical phenomena. We present experimental measurements of methane's thermal conductivity and compressional velocity to 25.1 and 45.1 GPa, respectively, at room temperature, and theoretical calculations of its equation of state, velocity, and heat capacity up to 100 GPa and 1200 K. Overall, these properties change smoothly with pressure and are generally unaffected by the imposed atomic structure; though we observe a discrete spike in conductivity near the I-A phase boundary. We cross-plot the thermal conductivity and compressional velocity with density for the primary “ice” constituents (methane, water, and ammonia) and find that methane and water are the upper and lower bounds, respectively, of conductivity and velocity in these systems. These physical properties provide critical insights that advance the modeling of thermo-chemical structures and dynamics within icy bodies.