Bulletin of the American Physical Society
16th APS Topical Conference on Shock Compression of Condensed Matter
Volume 54, Number 8
Sunday–Friday, June 28–July 3 2009; Nashville, Tennessee
Session T3: GS-3: Ices and Impacts |
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Chair: Rebecca Brannon, University of Utah Room: Hermitage C |
Thursday, July 2, 2009 9:00AM - 9:30AM |
T3.00001: Advances in Modeling Impacts onto H$_{2}$O Ice Invited Speaker: H$_{2}$O ice is a primary constituent of solid bodies in the outer solar system. Hence, understanding the response of H$_{2}$O ice to shock is particularly important in predicting and interpreting the outcome of natural collision events. The complex phase diagram and rheological properties of H$_{2}$O pose significant challenges to modeling shock processes in ice. We have developed a new multi-phase equation of state (EOS) and constitutive model for H$_{2}$O that are appropriate for the wide range of environmental conditions and impact parameters encountered in the solar system. The new tabular EOS includes 5 phases (vapor, liquid, ices Ih, VI, and VII) and allows for accurate predictions of peak and post-shock temperatures and the occurrence of phase changes. Unexpected phenomena are observed in simulations using the new EOS. For example, shock-induced formation and hysteretic unloading of dense, high-pressure phases leads to significant changes in the excavation flow field around impact craters compared to more homogeneous materials. The modified flow field results in observable differences in crater morphologies on ice-rich planetary surfaces compared to rock surfaces. With these improvements, we are able to model collisions onto H$_{2}$O ice with much better accuracy. [Preview Abstract] |
Thursday, July 2, 2009 9:30AM - 9:45AM |
T3.00002: Thermodynamics of Shock Waves in Ice-Sand Mixtures: Peak and Post-Shock Temperature Measurements Richard Kraus, Sarah Stewart, Achim Seifter, Andrew Obst Understanding the partition of energy in shocked mixtures of widely varying impedance is necessary to predict a wide range of phenomena, including phase changes, temperatures, and chemical reactions. In particular, we are interested in understanding the evolution of temperatures and internal energies from initial shock loading to equilibration. Subjected to an ideal strong shock, the mixture will initially load to a constant pressure; however, the temperature of each component will depend on its equation of state and loading path. Here, we present shock and release temperatures in a fine-grained 40:60 mixture of SiO$_{2}$ and H$_{2}$O ice subjected to planar shock. We find that the apparent temperatures are dominated by the more compressible component of the mixture. The shock temperatures are consistent with both components reaching the same pressure determined by the Hugoniot of the mixture. This is a challenging system to model because of the complicated wave interactions and dependence on length scales. We compare the experimental results to analytical and numerical solutions using a new equation of state for H$_{2}$O ice. [Preview Abstract] |
Thursday, July 2, 2009 9:45AM - 10:00AM |
T3.00003: Numerical Modeling of LCROSS experiment V.G. Sultanov, V.V. Kim, A.V. Matveichev, B.G. Zhukov, I.V. Lomonosov The mission objectives of the Lunar Crater Observation and Sensing Satellite (LCROSS) include confirming the presence or absence of water ice in a permanently shadowed crater in the Moon's polar regions. In this research we present results of numerical modeling of forthcoming LCROSS experiment. The parallel FPIC3D gas dynamic code with implemented realistic equations of state (EOS) and constitutive relations [1] was used. New wide--range EOS for lunar ground was developed. We carried out calculations of impact of model body on the lunar surface at different angels. Situations of impact on dry and water ice--contained lunar ground were also taken into account. Modeling results are given for crater's shape and size along with amount of ejecta. \\[4pt] [1] V.E.~Fortov, V.V.~Kim, I.V.~Lomonosov, A.V.~Matveichev, A.V.~Ostrik. Numerical modeling of hypervelocity impacts, Intern J Impact Engeneering, 33, 244-253 (2006) [Preview Abstract] |
Thursday, July 2, 2009 10:00AM - 10:15AM |
T3.00004: Formation of Pre-biotic Molecules in Shocked Astrophysical Ices Nir Goldman, I-F. William Kuo, Evan Reed, Laurence E. Fried We present herein \textit{ab initio} molecular dynamics (MD) simulations of peptide bond synthesis in shock compressed astrochemical mixtures such as found in comets and other celestial bodies. Given the likelihood of a CO$_{2}$-rich primitive atmosphere, it is probable that impact processes of icy interstellar masses were partially responsible for the creation of pre-biotic peptide (C---N) bonded materials on early Earth. To this end, we have studied C---N bond formation in a prototypical interstellar ice mixture shock compressed up to velocities close to Earth's escape velocity. Our results show that high shock velocities can drive the synthesis of a number of short-lived, exotic C---N bonded species at much high pressure-temperature conditions than previously thought. Stable amino acids are then formed upon quenching to lower temperature. Knowledge of chemical properties of these species under extreme thermodynamic conditions is essential for a complete understanding of the role of these impact processes in the formation of life-building compounds. [Preview Abstract] |
Thursday, July 2, 2009 10:15AM - 10:30AM |
T3.00005: Calculating protoplanet collisions in the early solar system Paul S. De Carli, Zhidong Xie, Thomas Sharp We study shock-synthesized high-pressure phases in meteorites in infer the conditions under which they formed. These phase are found in or adjacent to locally melted veins or pockets that formed on shock compression. The melt veins cooled by conduction to adjacent cooler material. We use static high pressure data to establish the pressure range over which the melt solidified and cooled and the observed phases formed. One may then calculate the shock temperature of the cooler material. In general, we know only that the initial temperature of the melt vein lies above the liquidus. In a recent observation, we have found a secondary melt zone adjacent to a vein. The width of this zone provides a measure of the peak temperature of the melt vein. Calculations of the thermal and pressure history of the melt vein indicates that this meteorite was subjected to shock pressures in the range of 18-22 GPa for a duration of at least a second. We use the Autodyn(TM)code to calculate impacts between meteorite parent bodies in the early solar system. We infer that this meteorite must have been at a depth of at least 10 km at the time of the impact that produced the observed high-pressure phases. [Preview Abstract] |
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