Abstract
The efficiency of heat transfer in the outer shell of icy satellites is
important to determine the evolution and thermal state of their interior
with major implications for the cooling behavior of an internal ocean.
In this study, we systematically investigate thermal convection in the
ice shell of Europa using an Arrhenius viscosity and accounting for ice
I material that is dependent on both grain size and strain rate. To this
end, we employ the geodynamical code GAIA [1] with a mixed rheology
approach similar to [2], and perform calculations in a 2D Cartesian
box and spherical annulus geometry for two values of the ice shell
thickness (i.e., 30 and 70 km). In our simulations, we test various
constant grain size values. In a first serie of simulations, we tested
the importance of the dislocation creep mechanism for modeling
convection in Europa’s ice shell. Our results show that, in a mixed
diffusion-dislocation creep rheology, diffusion creep is the dominant
heat transfer mechanism, similar to the study of [3]. A pure
dislocation creep rheology leads to a conductive ice shell. Dislocation
creep may become dominant if its rheological prefactor increases by
about 5 orders of magnitude, which even taking into account the
uncertainty associated with rheological measurements is considered
unrealistic. Additional simulations that use a mixed diffusion-basal
slip rheology show that for ice shells, basal slip may be a relevant
deformation mechanism in addition to diffusion creep. Another important
aspect is that the efficiency of heat transfer is larger for a thick ice
shell (70 km, compared to a thinner one (i.e., 30 km)). However, the
dimensional surface heat flow obtained for a thin ice shell is larger
than for a thicker one. This is caused by the rescaling of
non-dimensional parameters to a dimensional heat flow. References:
[1] Hüttig et al., PEPI 2013; [2] Schulz et al., GJI 2019;
[3] Harel et al., Icarus 2020.