Physics
Scientific paper
Dec 2007
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007agufmmr11a..07m&link_type=abstract
American Geophysical Union, Fall Meeting 2007, abstract #MR11A-07
Physics
3909 Elasticity And Anelasticity, 5422 Ices, 5460 Physical Properties Of Materials, 6221 Europa, 8160 Rheology: General (1236, 8032)
Scientific paper
The large icy satellites of the giant planets are subjected to periodic stress due to their resonance-effected orbital eccentricity. The dissipation of this tidal elastic energy represents a potentially significant internal energy source, the magnitude of which depends on the anelastic properties of the various material layers (ice, rock, etc.). In an icy satellite incorporating an internal ocean, as is suggested for Europa, most of the tidal dissipation (attenuation) occurs in the outer ice layer. Current models for attenuation in the icy shell rely on the inversion of a Maxwell model of steady-state rheology because, to date, no direct dynamic measurements of energy absorption in polycrystalline ice at low-stress/low-frequency planetary conditions have been reported. We are pursuing transient and steady-state creep as well as direct attenuation measurements on polycrystalline ice-I and on eutectic aggregates of ice-I and salt hydrates, such as those suggested to be present on the surface of Europa by the near-infrared spectral data. We focus primarily on system H2O-MgSO4 because it represents the best (binary-system) fit to the spectral data. Samples are fabricated using a misting/sifting technique in order to obtain fine grain-size, or, more accurately, eutectic colony-size (< 25 μm). Transformation of the time- domain data suggest the Maxwell model of steady state is inappropriate for understanding attenuation in pure ice, and wildly inappropriate for a ice-I/magnesium sulfate hydrate eutectic material, which demonstrates far higher attenuation (e.g., a factor of 102 at 1 Hz) than that predicted from the model. The absorption behavior of solid-state heterophase boundaries are argued as crucial in this behavior. Attenuation (cyclic compression- compression) experiments have commenced; we will report initial results, comparing these to earlier studies of the static response. Information gleaned from these experiment can help constrain models of crustal thickness and surface dynamics on Europa and icy satellites in general.
Cooper Reid F.
Goldsby David L.
McCarthy Carolyn Cordwell
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