Publication: Equilibrium Convection on a Tidally Heated
and Stressed Icy Shell of Europa for a Composite
Water Ice Rheology
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Publication Date
2010
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Springer Science Business Media
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Abstract
Water ice I rheology is a key factor for understanding the thermal and mechanical
state of the outer shell of the icy satellites. Ice flow involves several deformation mechanisms
(both Newtonian and non-Newtonian), which contribute to different extents depending on
the temperature, grain size, and applied stress. In this work I analyze tidally heated and
stressed equilibrium convection in the ice shell of Europa by considering a composite
viscosity law which includes diffusion creep, basal slip, grain boundary sliding and dislocation
creep, and. The calculations take into account the effect of tidal stresses on ice flow
and use grain sizes between 0.1 and 100 mm. An Arrhenius-type relation (useful for
parameterized convective models) is found then by fitting the calculated viscosity between
170 and 273 K to an exponential regression, which can be expressed in terms of preexponential
constant and effective activation energy. I obtain convective heat flows between
*40 and *60 mW m-2, values lower than those usually deduced (*100 mW m-2) from
geological indicators of lithospheric thermal state, probably indicating heterogeneous tidal
heating. On the other hand, for grain sizes larger than *0.3 mm the thicknesses of the ice
shell and convective sublayer are*20–30 km and*5–20 km respectively, values in good
agreement with the available information for Europa. So, some fundamental geophysical
characteristics of the ice shell of Europa could be arising from the properties of the composite
water ice rheology.