Publication: Heat flow and thickness of a convective ice shell on Europa for grain
size-dependent rheologies
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2007
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Elsevier Science B.V., Amsterdam
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Abstract
Although it is mostly accepted that the lower part of the ice shell of Europa is actively convective, there is still much uncertainty about the flow
mechanism dominating the rheology of this convective layer, which largely depends on the grain size of the ice. In this work, we examined thermal
equilibrium states in a tidally heated and strained convective shell, for two rheologies sensitive to grain size, grain boundary sliding and diffusion
creep. If we take a lower limit of 70 mWm−2 for the surface heat flow, according to some geological features observed, the ice grain size should
be less than 2 or 0.2 mm for grain boundary sliding or diffusion creep respectively. If in addition the thickness of the ice shell is constrained to a
few tens of kilometers and it is assumed that the thickness of the convective layer is related to lenticulae spacing, then grain sizes between 0.2 and
2 mm for grain boundary sliding, and between 0.1 and 0.2 mm for diffusion creep are obtained. Also, local convective layer thicknesses deduced
from lenticulae spacing are more similar to those here derived for grain boundary sliding. Our results thus favor grain boundary sliding as the
dominant rheology for the water ice in Europa’s convective layer, since this flow mechanism is able to satisfy the imposed constraints for a wider
range of grain sizes.