37th DPS Meeting, 4-9 September 2005
Session 63 Galilean Satellites
Oral, Friday, September 9, 2005, 9:00-10:30am, Law LG19

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[63.06] Tidal Stress on Europa: Sensitivity to Ice Shell Thickness

T.A. Hurford, R. Greenberg (University of Arizona)

On Europa, tidal stress computed with a thin-shell approximation have been used successfully to explain many characteristics of the tectonic features observed (Helfenstein and Parmentier. 1985. \emph{Icarus} \textbf{61}.; McEwen. 1986. \emph{Icarus} \textbf{321}.; Greenberg \emph{et al.} 1998. \emph{Icarus} \textbf{135}.; Greenberg and Geissler. 2002. \emph{Meteoritics and Planetary Science} \textbf{37}.). For example, cycloidal cracks have been reproduced by tracking crack propagation as the diurnally varying tidal stresses exceed the tensile strength of the surface ice (Hoppa \emph{et al.} 1999. \emph{Icarus} \textbf{153}; Sarid \emph{et al.} 2005. DPS). The thin shell approximation assumes the outer layer is an elastic sheet, decoupled from the deeper interior of the body by a fluid layer. The sheet deforms to fit the tidal figure taken by the body's interior, producing stress on the surface.

To compute Europa’s tidal deformation with a finite thickness to the outer elastic shell, we treat Europa as an incompressible body with layers homogeneous in density and rigidity (Sabadini and Vermeersen. 2004. Global Dynamics of the Earth). This method predicts the stress on its surface for various assumed internal structures. We find that the stress on Europa's surface is sensitive to the thickness of the icy crust. For a thick ice layer, approaching the thickness of the total H2O layer, the stresses are qualitatively different from thin ice shells, predicting compression along the tidal bulges. These stresses might be similar to the stresses produced on moons with deep subsurface oceans, like Ganymede. Even if the ice is only 10 or 20 km thick, there are substantial differences in the theoretical stresses from those predicted by the traditional thin-sheet method. Using stresses produced by multi-layered models of Europa to understand the tectonic fabric of its surface has the potential to constrain the thickness of Europa's icy crust.

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