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Inferring the Mean Effective Elastic Thickness of the Outer Ice Shell of Enceladus from Diurnal Crustal Deformation
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  • Alexander Berne,
  • Mark Simons,
  • James Tuttle Keane,
  • Ryan S. Park
Alexander Berne
California Institute of Technology

Corresponding Author:[email protected]

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Mark Simons
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James Tuttle Keane
NASA Jet Propulsion Laboratory, California Institute of Technology
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Ryan S. Park
Jet Propulsion Laboratory
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The thickness of the outer ice shell plays an important role in several geodynamical processes at ocean worlds. Here we show that observations of tidally-driven diurnal surface displacements can constrain the mean effective elastic thickness, ˜del, of the ice shell. Such estimates are sensitive to any significant structural features that break spherical symmetry such as faults and lateral variation in ice shell thickness and structure. We develop a finite-element model of Enceladus to calculate diurnal tidal displacements for a range of ˜del values in the presence of such structural heterogeneities. We find that the presence of variations in ice shell thickness can significantly amplify deformation in thinned regions. If major faults are also activated by tidal forcing—such as Tiger Stripes on Enceladus—their characteristic surface displacement patterns could easily be measured using modern geodetic methods. Within the family of Enceladus models explored, estimates of ˜del that assume spherical symmetry a priori can deviate from the true value by as much as ~ 20% when structural heterogeneities are present. Such uncertainty is smaller than that found with approaches that rely on static gravity and topography (~ 250%) or analyzing diurnal libration amplitudes (~ 25%) to infer ˜del at Enceladus. As such, despite the impact of structural heterogeneities, we find that analysis of diurnal tidal deformation is a relatively robust approach to inferring ˜del.