Equilibrium Convection on a Tidally Heated and Stressed Icy Shell of Europa for a Composite Water Ice Rheology

Water ice I rheology is a key factor for understanding the thermal and mechanical\udstate of the outer shell of the icy satellites. Ice flow involves several deformation mechanisms\ud(both Newtonian and non-Newtonian), which contribute to different extents depending on\udthe temperature, grain size, and applied stress. In this work I analyze tidally heated and\udstressed equilibrium convection in the ice shell of Europa by considering a composite\udviscosity law which includes diffusion creep, basal slip, grain boundary sliding and dislocation\udcreep, and. The calculations take into account the effect of tidal stresses on ice flow\udand use grain sizes between 0.1 and 100 mm. An Arrhenius-type relation (useful for\udparameterized convective models) is found then by fitting the calculated viscosity between\ud170 and 273 K to an exponential regression, which can be expressed in terms of preexponential\udconstant and effective activation energy. I obtain convective heat flows between\ud*40 and *60 mW m-2, values lower than those usually deduced (*100 mW m-2) from\udgeological indicators of lithospheric thermal state, probably indicating heterogeneous tidal\udheating. On the other hand, for grain sizes larger than *0.3 mm the thicknesses of the ice\udshell and convective sublayer are*20–30 km and*5–20 km respectively, values in good\udagreement with the available information for Europa. So, some fundamental geophysical\udcharacteristics of the ice shell of Europa could be arising from the properties of the composite\udwater ice rheology