Ice Attenuation Properties at Low Frequencies and Low Stresses Relevant to Planetary Bodies

Abstract:

The mechanical properties of water ice have been much studied in laboratory but at stresses and forcing frequencies that are in discrepancy with the conditions relevant to the shells of giant planet satellites. As a result the anelastic response of ice, and associated energy dissipation, are not well understood and modeled.

The Planetary Tides Simulation Facility (PTSF) installed at the Jet Propulsion Laboratory (California Institute of Technology) has the capability to quantify the anelastic behavior of ice at stresses between 20-100 kPa and over a frequency range of 3x10^-6 to 0.1 Hz simulating tidal forcing frequencies relevant to many icy satellites, including Europa, Enceladus, and Charon.

Data are best fitted by the Andrade model, i.e., a function that accounts for anelasticity in the form of two parameters: a parameter β function of the density of defects in the material and a parameter α that captures the complexity of the defect distribution. From preliminary results we have derived empirical expressions of the fitting parameter β in terms of the intrinsic properties of the sample (i.e., viscosity and elastic moduli), leading to a function that is uniquely function of the parameter α. Combining our results with previous studies we have established trends for describing the behavior of α as a function of testing conditions and material properties (e.g., microstructure, presence of melt).

We will present applications of these results to icy satellites, and especially Europa.

Acknowledgement: Part of this work is been carried out at the Jet Propulsion Laboratory, California Institute of Technology under contract to NASA. Government sponsorship acknowledged.