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

Abstract

Water ice I rheology is akey factorfor llllderstanding 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 bOlmdary sliding and dislo cation creep, and. The calculations take into aCcOllllt 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 fOlllld then by fi tting the calculated viscosity between 170 and 273 K to an exponential regression, which can be expressed in terms of pre exponential constant and effective activation energy.

The Growth of Europa's Icy Shell: Convection and Crystallization

“…In this subsection, we consider ice deformation through diffusion creep and GSS creep, as dislocation creep dominates at higher stresses (>1 MPa) than thought to be broadly present in the Europan ice shell (10 −4 –0.1 MPa; Barr & Pappalardo, 2005) and is generally ignored in shell rheological studies (Barr & McKinnon, 2007; McKinnon, 2006; Ruiz, 2010). To capture GSS creep within our effective viscosity, we will use the activation energy for GBS creep specifically ( Q = 49 kJ/mol) in tandem with the Christensen (1984) approximation, as BS creep dominates over GBS in very low‐temperature conditions that will be present in the rigid lid of the ice shell (Barr & Showman, 2009), and not the ductile, convective interior.…”

Domes, pits, and small chaos on Europa produced by water sills

“…A compilation of published values, however, indicates great variability from hundreds of meters to a few kilometers [ Billings and Kattenhorm , ; Nimmo and Manga , ]. The equilibrium thickness of Europa's ice shell has a conductive layer extending to depths of ~10 km thick for a wide range of ice rheologies [ Ruiz , ]. Given that pits, domes, and chaos are among the younger features on Europa [ Pappalardo et al , ], assuming an ice shell thickness similar to equilibrium values seems reasonable.…”

“…For an ice shell and ocean at thermal equilibrium, the liquid water temperature is between 269 and 273 K [ Ruiz , ] and the temperature in the ice shell at the equator varies from 110 K at the surface to the ocean temperature at the shell bottom, with an average of 163 K. Since we suppose the sill intrudes relatively deep into the ice shell, we use an average temperature difference of 60 K between the liquid water and the surrounding ice. Using values for the parameters listed in Table , we calculate a timescale for dyke arrest by solidification equal to the timescale necessary for the frozen margin thickness to reach the dyke width; this timescale is between 4×10 5 and 4×10 7 s for dyke widths between 10 cm and 1 m as calculated in section 3.1.…”

Thermal convection in ice sheets

“…59, No. 213, 2013 *Convection is thought to occur on some of the Galilean satellites of Jupiter (Reynolds and Cassen, 1979), and possibly the Saturnian moons (Ellsworth and Schubert, 1983), with most recent attention being on the Jovian moon Europa (Pappalardo and others, 1998;Ruiz, 2010), but this is essentially mantle convection, and the setting is quite different to that considered here. kilometres-wide fine-scale tributaries that are revealed in the astonishing figure 1 of his paper (but which, incidentally, are not visible in the presumably lower-resolution image at the web page he cites,* and which latter has also been published (Rignot and others, 2011)).…”