Ice dynamic recrystallization within Europa's ice shell: Implications for solid-state convection.

Solid-state convection has been proposed to occur within Europa's ice shell based both on the interpretation of observed geological activity during Galileo spacecraft exploration and theoretical investigations. Laboratory experiments have investigated the effect of grain size insensitive creep and grain size sensitive creep on the ductile behaviour of polycrystalline ice. The ice grain size and the ice impurities content and, consequently, the viscosity of the ice within Europa's ice shell are poorly constrained, limiting the possibility to understand if solid-state convection can occur under Europa's ice shell conditions. To investigate how diurnal tidal flexing and the internal dynamics of Europa's ice shell influence the ice grain crystals' evolution, we adopted a thermal-mechanical numerical model that uses finite differences and marker-in-cell techniques, implementing the dynamic recrystallization of the ice and the ice grain evolution in a self-consistent way with the numerical model. We found that solid-state convection within Europa's ice shell can occur if it is diurnally tidally deformed, as the tidal stresses within the ice shell operate to reduce the ice grain sizes and the ice viscosity. We discuss future radio science experiments, in combination with radar sounder investigations, that will be capable of characterizing the possible presence of solid-state convection within Europa's ice shell. • Numerical solid-state convection model of self-consistent ice grain size evolution in Europa's ice shell • The diurnal tidal flexing of the ice shell influences the ice crystals evolution and, consequently, the onset of convection, and its stability. • The tidal stresses within the ice shell reduce the ice grain size, allowing the onset of solid- state convection within Europa's ice shell [ABSTRACT FROM AUTHOR]