Shock and Post-Shock Temperatures in an Ice-Quartz Mixture: Implications for Melting During Planetary Impact Events

Details Shock and Post-Shock Temperatures in an Ice-Quartz Mixture: Implications for Melting During Planetary Impact Events Shock and Post-Shock Temperatures in an Ice-Quartz Mixture: Implications for Melting During Planetary Impact Events

Dec 2009

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009agufm.p23e..07s&link_type=abstract

American Geophysical Union, Fall Meeting 2009, abstract #P23E-07

Physics

[3939] Mineral Physics / Physical Thermodynamics, [3944] Mineral Physics / Shock Wave Experiments, [5420] Planetary Sciences: Solid Surface Planets / Impact Phenomena, Cratering, [5422] Planetary Sciences: Solid Surface Planets / Ices

Scientific paper

Melting of H2O ice during planetary impact events is a widespread phenomenon. On planetary surfaces, ice is often mixed with other materials; yet, at present, how energy is partitioned between the components of a shocked mixture is still an open question in the shock physics community. Knowledge of how energy is partitioned to the ice component would help to predict and interpret a wide range of processes including shock-induced melting and chemistry. In this work, we construct a conceptual framework to elucidate the thermodynamic pathways of the components in a mixture and define three broad regimes based on the relative particle size with respect to the thickness of the shock front: (1) small length scale mixtures that reach pressure and temperature equilibration immediately behind the shock front; (2) intermediate length scales where pressure but not temperature equilibrium is achieved behind the shock front; and (3) long length scales where pressure equilibration requires multiple wave reflections. Here, we conduct shock temperature experiments in an H2O ice-SiO2 quartz mixture in the intermediate length scale regime. For shock pressures between 8 and 23 GPa, we determine the shock and post-shock temperatures of the H2O component. We find that the mixture is shocked to pressure equilibrium but not thermal equilibrium immediately behind the shock front. The shock and post-shock temperatures of the H2O component demonstrate that it is shocked to the principal Hugoniot. Therefore, in the intermediate length scale regime, the shock energy initially partitions according to the Hugoniots of the components. At present, the complexity of the thermodynamics of icy mixtures are not captured by available hydrocodes; however, using educated constraints on length and time scales, more accurate estimates of volumes of melt may be attained. We discuss energy partitioning in mixtures over the wide range of length and time scales encountered during planetary impact events. In some cases, the criteria for shock induced melting are the same as for pure H2O ice.

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