Bulletin of the American Physical Society
2005 14th APS Topical Conference on Shock Compression of Condensed Matter
Sunday–Friday, July 31–August 5 2005; Baltimore, MD
Session Q2: Geophysics & Planetary Science I |
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Chair: Karin Louzada, Harvard University Room: Hyatt Regency Constellation C |
Wednesday, August 3, 2005 9:30AM - 9:45AM |
Q2.00001: Ice-silicate fractionation among icy bodies due to the difference of impact strength between ice and ice-silicate mixture Daisuke Tomizuka, Masahiko Arakawa Laboratory experiments on the impact disruption of ice-silicate mixtures were conducted to clarify the accretion process of small icy bodies. Since the icy bodies are composed of ice and silicates with various porosities, we investigated the effect of porosity on the impact disruption of mixtures. We tested the mixture target with the mass ratio of ice to silicate, 0.5 and with 5 different porosities (0, 12.5, 25, 32, 37 {\%}) at the impact velocities of 150 to 670 m/s. The silicate mass ratio was changed from 0 to 0.5 in steps of 0.1 at a porosity of 12.5 {\%} and a constant impact velocity of about 300 m/s. The impact strength of the mixture was found to decrease with increasing porosity and the silicate mass ratio between 0.1 and 0.5 could enhance the strength of the icy target. The observed dependence of the impact strength on the porosity is opposite to that observed for pure ice. This difference could play an important role in ice-silicate fractionation during the accretion process. Because, ice rich bodies are easily broken as the porosity decreases in their evolution, the collisional growth could be prohibited. On the other hand, among the silicate rich bodies the collisional growth could be enhanced. [Preview Abstract] |
Wednesday, August 3, 2005 9:45AM - 10:00AM |
Q2.00002: Planetary Implications of the Hugoniot of Liquid Deuterium D.D. Sasselov, W.J. Nellis The question as to the correct Hugoniot of liquid deuterium has been resolved recently with high velocity impactors accelerated with hemispherically converging systems driven by high explosives and with planar systems driven by pulsed magnetic fields (1). Determination of this Hugoniot has a significant influence on the equation of state of dense fluid hydrogen, which in turn constrains models of the interiors of Jupiter and Saturn, as well as extrasolar giant gas planets (2). Prior to these measurements there was considerable uncertainty as to the size of Jupiter’s core and the amount of metals (oxygen, carbon, nitrogen, etc) mixed throughout its H-He envelope. A principal result of these Hugoniot measurements is to demonstrate that Jupiter has a small rocky core and a substantial amount of metals dissolved throughout its H-He envelop. A more general effect is to show that most giant planets appear to be similar to this picture of Jupiter, which in turn identifies unusual giant planets for further study. \newline \newline (1) G. V. Boriskov et al, {\textit Phys. Rev. B} {\textbf 71}, 092104 (2005). \newline (2) M. Konacki et al, {\textit ApJ}. {\textbf 624}, 372 (2005). [Preview Abstract] |
Wednesday, August 3, 2005 10:00AM - 10:15AM |
Q2.00003: Experimental Study of Transition of Jupiter and Saturn Atmosphere to Conducting State V. Ya. Ternovoi, S.V. Kvitov, D.N. Nikolaev, A.A. Pyalling, A.S. Filimonov, V.E. Fortov A modified equation of state of helium-hydrogen mixtures was used for 1D hydrodynamic simulation of performed experiments with multiple shock compression of Jupiter and Saturn model atmospheres. That permitted us to obtain the isentropic compression at third and later steps of compression in the pressure region 20 -150 GPa. It was shown that the helium-hydrogen mixtures become conductive due to appearance of hydrogen conductance. The intervals of pressure - temperature - density states of these transitions are 27-36 GPa - 4400-5000 K - 0.36-0.41 g/cc for Jupiter and 50-70 GPa - 3100-3300 K - 0.5-0.57 g/cc for Saturn in accordance with our new and previous experiments with the pure hydrogen and gas mixtures. [Preview Abstract] |
Wednesday, August 3, 2005 10:15AM - 10:30AM |
Q2.00004: Shock Demagnetization of Pyrrhotite (Fe$_{7}$S$_{8})$ -- Implications for the Martian Crust and Meteorites Karin Louzada, Sarah Stewart, Benjamin Weiss After cessation of the dynamo on Mars, giant impact events demagnetized large regions of the crust. Models of shock pressure decay indicate that the demagnetized zones are bound by peak shock pressures between 1 and 3 GPa. Static pressure experiments at room temperature on pyrrhotite (a common carrier of magnetization in Martian meteorites) demonstrate it undergoes a magnetic phase transition at $\sim $2.8 GPa, with rapid loss of magnetization above 1 GPa. We performed the first planar shock recovery experiments on natural pyrrhotite using the 40-mm gas gun in the Shock Compression Laboratory at Harvard. Post-shock magnetic measurements show that pyrrhotite indeed demagnetizes significantly ($\sim $85-90{\%}) due to shock in the pressure range inferred around Martian impact basins, however, we were unable to completely demagnetize at 4 GPa. Permanent changes to the magnetic properties are an increase in the saturation remanence and the mean destructive field (the field required to reduce the remanence to 1/2 its initial value), indicating that shocks harden the coercivity. We conclude that pyrrhotite is a candidate for the Martian crust and that pyrrhotite in meteorites shocked to modest pressures may retain a pre-shock remanence. [Preview Abstract] |
Wednesday, August 3, 2005 10:30AM - 11:00AM |
Q2.00005: Microbial Life and Shock Compression - Life or Death? Invited Speaker: Extreme shock compressions represent a threat to organisms that inhabit planetary surfaces such as rocks. For example, a giant impact on a planetary surface can sterilise the surrounding region by passage of the resulting shock wave. Modelling of the limit of the zone of lethality depends on a knowledge of the response of micro-organisms to extreme shock. Similarly high speed ejecta can be launched into space from an impact site and may carry viable micro-organisms if they can survive the shock of the launch. Or potentially a rocky body arriving from space may introduce life to the Earth, provided the putative organisms can survive the shock of the impact (amongst other hazards). The results of a variety of laboratory experiments on shock compression of micro-organisms will be presented and discussed (with some data from the author and some from the literature). Some of the experiments involved firing spore and microbe laden projectiles at speeds of up to 6 or 7 km s$^{-1}$ into a variety of targets. Other experiments used flying plate techniques to subject layers of spores to extreme shocks. The conclusion is that micro-organisms can survive extreme shock pressures (10's of GPa) in short duration events, albeit with a very small, but measurable, survival rate. These pressures cover the range likely to be found in giant impacts from space for example. [Preview Abstract] |
Wednesday, August 3, 2005 11:00AM - 11:15AM |
Q2.00006: Quartz and Hydrous Iron-oxide Impactites from the Bee Bluff Structure of South Texas R.A. Graham, M. Martin, N.N. Thadhani, B. Morosin Breccia impactite samples are found to have been strongly influenced by high pressure shock waves controlled by the thin veneer of sandstone, siltstone and a thin layer of iron-rich siltstone target rocks. Carrizo sandstone is converted to a hard grey breccia containing comminuted quartz bound with tightly adhering alpha goethite. Transformations in the hydrous iron-oxide binder and hydrous iron-rich siltstone in virtually all impactite samples dominate the scientific issues. Goethite is found in numerous samples including spherules loose on the site, `sky bombs,' in suevite in a Rosetta Stone containing five different impactite clasts, and in samples with hydrodynamic instabilities. Localized melting in quartz at particle interfaces is observed throughout. SEM and EDX analysis shows regions of fused quartz, some in the ballen structure characteristic of lechatleriete. Acicular goethite nanocrystals and submicron spheres are abundant. The high pressure-high temperature pulse of the impact produces an environment in which transformation to the iron-rich hydrous oxide to goethite, hematite and steam is to be expected. [Preview Abstract] |
Wednesday, August 3, 2005 11:15AM - 11:30AM |
Q2.00007: Experimental Hugoniot Data of Porous Silica D.L.A. Cross, D.J. Chapman, J. Borg, J. Cogar, I.G. Cullis, K. Tsembelis, W.G. Proud A series of impact experiments were conducted at Cambridge University, Cavendish Laboratory to experimentally determine the Hugoniot of various densities of porous silica dust. The densities investigated were 0.1, 0.25, and 0.77 g cm-3. The experiments were conducted up to ca. 2.3 GPa in the Silica. Individual experimental results and the resulting P-V and Us-up Hugoniot are discussed and presented. [Preview Abstract] |
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