Mathematics – Logic
Scientific paper
Dec 2007
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007agufmmr54a..01p&link_type=abstract
American Geophysical Union, Fall Meeting 2007, abstract #MR54A-01
Mathematics
Logic
5199 General Or Miscellaneous, 5420 Impact Phenomena, Cratering (6022, 8136), 5460 Physical Properties Of Materials, 5470 Surface Materials And Properties
Scientific paper
The cratering process is strongly affected by the physical and chemical properties of target material, including porosity, volatile content and natural mixtures of diverse rocks. On Earth craters in water-saturated sediments are larger than their energy-equivalents in dry soils, which, in turn, are larger than their energy-equivalents in crystalline rocks. On Mars, the distinctly lobate outer boundary (and sometimes several overlapping sets of flow lobes) of impact crater ejecta blankets suggests mobilization of subsurface volatiles, in contrast to evidence from the much drier Moon and Mercury, where craters are surrounded by ballistically emplaced ejecta. A thorough understanding of the behavior and influence of material characteristics on the impact process is crucial for using impact cratering as a tool to better understand the physical, geological, and biogeochemical processes on a given planetary body. The presence of volatiles, namely water, in the target may affect shock propagation and consequently target melting and the final crater morphology. When the target is a mixture of materials with very different impedance, as is the case for rocks and water, the shock wave propagation may be affected by the interaction of the original shock wave with shocks reflected at material boundaries. Single- and multiple-shocked materials experiencing the same peak shock pressure will reach substantially different thermodynamic states, with the multiple-shocked material having lower shock temperature and shock entropy. As a result, for mixtures of materials with very different impedances the maximum shock pressure alone may not be the best criterion for estimating melting and vaporization. Water vaporization may also influence the ejection process by affecting the amount and dispersion of shocked ejecta. We carried out a series of numerical studies to investigate the effect of water and/or ice in the target on the cratering process. Initial results indicate that there is no single incipient and complete shock pressure for shock melting of ice in permafrost. These values depend on dry rock porosity and on the amount and shape of the water/ice inclusions. Neglecting to properly address target properties in numerical models may ultimately limit our understanding of the cratering process and result in predictions that are in disagreement with observations.
Artemieva Natalia
Ivanov Boris
Pierazzo Elisabetta
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