Preliminary Comparison of the Attenuation Properties of Polycrystalline Water Ice and CO2 Clathrate Hydrates

Details Preliminary Comparison of the Attenuation Properties of Polycrystalline Water Ice and CO2 Clathrate Hydrates Preliminary Comparison of the Attenuation Properties of Polycrystalline Water Ice and CO2 Clathrate Hydrates

Sep 2009

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009dps....41.6108c&link_type=abstract

American Astronomical Society, DPS meeting #41, #61.08

Astronomy and Astrophysics

Astronomy

Scientific paper

We will present measurements of the attenuation properties of CO2 clathrate hydrates and polycrystalline water ice. These laboratory data are necessary to support models of tidal heating within the icy shells of Europa and Enceladus. Particularly, the attenuation properties of clathrates, likely involved in Enceladus’ outgassing, remain unconstrained. Samples are synthesized from ice seeds with a grain size of 150 - 425 microns. Seeds of carbon dioxide clathrate hydrates are synthesized within a high pressure - low temperature vessel, by reaction of CO2 at 30-40 bars with the ice seeds at -10 to -1 °C. Solid samples are produced from the compaction of the seeds at -80 °C, under vacuum and at a 100-MPa pressure applied over several hours. The microstructure of the samples before and after testing is characterized by optical cryo-microscopy and by Cryo - Scanning Electron Microprobe (CryoSEM). The CryoSEM is equipped with an Energy Dispersive Spectrometer, which provides elemental composition of the samples. Microstructural evolution and potential changes in composition resulting from clathrate dissociation can be assessed with these techniques. Cyclic loading measurements are being conducted with the Planetary Tides Simulation Facility at JPL, a cryogenic uniaxial compression system, within the frequency range 3x10-6 - 10-3 Hz, which encompasses the orbital frequencies of Enceladus and Europa. We will compare and contrast the attenuation observed for clathrate hydrates and polycrystalline ice in order to characterize the microstructural mechanisms driving dissipation in these samples. We will address the implications of these new observations in the context of icy satellites.
Acknowledgements: MC is supported by a NASA Postdoctoral Program Fellowship, administered by Oak Ridge Associated Universities. This work has been conducted at the Jet Propulsion Laboratory, California Institute of Technology, under contract with NASA. Copyright 2009, California Institute of Technology. Government sponsorship acknowledged.

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