P083-07
Effect of temperature-dependent material properties on ice shell convection
Wednesday, 16 December 2020: 05:54
Virtual
Evan Carnahan, University of Texas at Austin, Austin, TX, United States, Natalie Soheila Wolfenbarger, University of Texas at Austin, Institute for Geophysics, Austin, TX, United States, Jake Jordan, Rice University, Houston, TX, United States and Marc A Hesse, The University of Texas at Austin, Geological Sciences, Austin, TX, United States
Abstract:
Ice shell dynamics are an important control on the habitability of icy ocean worlds. Convection governs ice shell thickness, the rate of heat loss, and material transport across the ice. The convective stability of the ice shell is controlled by material properties of the ice (viscosity, density, heat capacity, and thermal conductivity). Temperatures in the ice shell can range from 30 K to 273 K, which leads to large variations in these properties. For the thermal conductivity of ice Ih there is a large spread in the experimental data at low temperatures. We fit a comprehensive collection of previously published thermal conductivity data that spans the range of temperatures relevant to icy ocean worlds. We find that the Hobbs conductivity model used in planetary science is a lower bound and underestimates the low-temperature thermal conductivity by more than a fifth. Assuming constant thermal conductivity, as is commonly done, underestimates the thermal conductivities at the surface by an order of magnitude.
We present a systematic study evaluating the effect of temperature-dependent material properties, tidal heating, and surface temperature on the convective stability and ice shell response time. We explore a parameter range suitable for the ice shells of Europa, Titan, and Enceladus. We find that the choice of thermal conductivity relationship can shift the critical Rayleigh number for the onset of convection by more than one order of magnitude and is larger than the effect of tidal heating on the stability of the ice shell. This is of importance to Europa and Enceladus where the majority of possible ice shell parameter combinations are below the critical Rayleigh number for any thermal conductivity relationship. Furthermore, we show that including temperature-dependent specific heat capacity decreases the energy stored in the conductive lid which reduces the response timescale of the ice shell to thermal perturbations by approximately a quarter.
