Physics
Scientific paper
Dec 2008
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008agufmmr12a..05s&link_type=abstract
American Geophysical Union, Fall Meeting 2008, abstract #MR12A-05
Physics
3919 Equations Of State, 3944 Shock Wave Experiments, 5420 Impact Phenomena, Cratering (6022, 8136), 5422 Ices, 5460 Physical Properties Of Materials
Scientific paper
New experimental data and cratering calculations illustrate the complex response of H2O ice to shock compression. We present peak and post-shock temperature measurements from shocked H2O ice. In experiments with shock pressures between 8 and 14 GPa, initially ~150 K ice is compressed to a supercritical state. In the time frame of the experiment, the supercritical H2O releases to the saturation vapor curve and does not achieve full decompression. Further decompression requires a significant volume expansion. In general, the time scale of expansion will depend on the internal energy and the surrounding conditions (e.g., confined or unconfined). The temperature data validate a new 5-Phase hydrocode equation of state model for H2O, which includes ice Ih, VI, VII, liquid, and vapor. Using the 5-Phase EOS, we model impact cratering onto icy satellites. After passage of the impact-generated shock wave, material beneath the growing transient crater has a layered composition: vapor, liquid, high- pressure phases (ices VII and VI), and ice Ih. The high pressure phases cannot fully decompress without a large volume increase. Thus, these phases initially unload to the pressure along the phase boundary; this pressurized region affects the excavation flow field. The changes in crater excavation lead to differences in crater size and amount of ejecta compared to excavation in a homogeneous target. The differences are significant for large craters (e.g., complex craters on Ganymede and Callisto). The modified excavation flow field also concentrates highly shocked material in the crater floor. In cases where a large, hot plug is buried during crater collapse, explosions occur as the material cools by transforming to vapor, producing features similar to central pits observed on Ganymede, Callisto, and Mars. The behavior of shocked H2O ice during decompression should lead to a variety of features that depend on the ambient conditions specific to each icy planetary body.
Obst Andrew W.
Seifter Achim
Senft Laurel E.
Stewart Sarah T.
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