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Shock experiments give a unique insight into the behavior of matter subjected to extremely high pressures and temperatures. Understanding the behavior of materials under such extreme conditions is key to modeling material failure and deformation dynamics under impact. While studies on pure silica are extensive, the shock behavior of other commercial silicates that contain additional oxides has not been systematically investigated. To better understand the role of composition in the dynamic behavior of silicates, we performed laser-driven dynamic compression experiments on soda-lime glass (SLG) up to 315 GPa. Using the accurate pulse shaping offered by the long pulse laser system at the Matter in Extreme Conditions end-station at the Linac Coherent Light Source, SLG was shock compressed along the Hugoniot to multiple pressure-temperature points. Velocity Interferometer System for Any Reflector was used to measure the velocity and determine the pressure inside the SLG. The U s –u p relationship obtained agrees well with the previous parallel plate impact studies. Within the error bars, no transformation to the crystalline phase was observed up to 70 GPa, which is in contrast to the behavior of pure silica under shock compression. Our studies show that the glass composition strongly influences the shock compression behavior of the silicate glasses. [ABSTRACT FROM AUTHOR]

The effect of grain size and moisture content on the dynamic macroscopic response of granular geological materials was explored by performing uniaxial planar impact experiments on high purity, Oklahoma #1, sand samples composed of either fine (75-150 µm) or coarse (425-500 µm) grain sizes in either dry or fully water-saturated conditions. Oklahoma #1 sand was chosen for its smooth, quasi-spherical grain shapes, narrow grain size distributions, and nearly pure SiO2 composition (99.8wt. %). The water-saturated samples were completely saturated ensuring a two-phase mixture with roughly 65% sand and 35% water. Sand samples were dynamically loaded to pressures between 1 and 11GPa. Three-dimensional meso-scale simulations using an Eulerian hydrocode, CTH, were created to model the response of each sand sample. Multi-phase equations of state were used for both silicon dioxide, which comprised individual sand grains, and water, which surrounded individual grains. Particle velocity profiles measured from the rear surface of the sand, both experimentally and computationally, reveal that fine grain samples have steeper rise characteristics than coarse grain samples and water-saturated samples have an overall much stiffer response than dry samples. The experimentally determined particle velocity vs. shock velocity response of dry sand was linear over this pressure range, with little difference between the two grain sizes investigated. The experimental response for the water saturated sand exhibited a piecewise continuous response with a transition region between particle velocities of 0.6 km s-1 and 0.8 km s-1 and a pressure of 4.5-6GPa. Hypotheses for the cause of this transition region are drawn based on results of the meso-scale simulations. [ABSTRACT FROM AUTHOR]

Shock compression experiments on natural compositions are imperative to accurately model planetary accretion and the interior dynamics of planets. Combining shock compression experiments from the Sandia Z Machine and the OMEGA EP laser facility with density functional theory‐based molecular dynamics calculations, we report the first pressure‐density‐temperature (P‐ρ‐T) relationship of natural iron (Fe)‐bearing olivine ((Mg0.91Fe0.09)2SiO4) on the principal Hugoniot between 166 and 1,465 GPa. Additionally, we report the first reflectivities of natural olivine liquid in this pressure range. Compared to the magnesium‐endmember forsterite (Mg2SiO4), the presence of Fe in typical mantle abundance (∼9 wt% FeO) alters the US‐uP relation of olivine. On the other hand, the shock temperature and reflectivity of olivine are indistinguishable from forsterite where experimental conditions overlap. Both forsterite and olivine increase in reflectivity (and hence optical conductivity) with increasing temperature, with a maximum reflectivity of ∼31% at shock velocities greater than 22 km/s (∼800 GPa). Plain Language Summary: Olivine is the most abundant mineral in Earth's upper mantle and in the mantles of other rocky bodies in the Solar System. While previous studies of this material have focused on iron‐free compositions, natural olivine contains varying amounts of iron. The data presented here describe how olivine responds to shock waves, which are important for understanding the outcomes of collisions onto growing planets. With these data, we can more robustly model the pressure and temperature conditions reached in impact situations, as well as the relative amounts of melting and vaporization that will occur from an impact. These parameters are key to understanding the chemistry that can occur as planets grow. We have also found that olivine liquid becomes highly reflective at high temperatures, which suggests that it is electrically conductive. This observation is important for understanding the generation of magnetic fields in very hot or molten planets. Key Points: Combined dynamic compression data with computations to define the pressure‐density‐temperature relation on the Hugoniot of olivineThe principal Hugoniot of olivine diverges from Fe‐free forsterite over the experimental conditionsOlivine liquid is optically conductive at high temperatures and high pressures [ABSTRACT FROM AUTHOR]

The physical processes during planet formation span a large range of pressures and temperatures. Giant impacts, such as the one that formed the Moon, achieve peak pressures of 100s of GPa. The peak shock states generate sufficient entropy such that subsequent decompression to low pressures intersects the liquid‐vapor phase boundary. The entire shock‐and‐release thermodynamic path must be calculated accurately in order to predict the post‐impact structures of planetary bodies. Forsterite (Mg2SiO4) is a commonly used mineral to represent the mantles of differentiated bodies in hydrocode models of planetary collisions. Here, we performed shock experiments on the Sandia Z Machine to obtain the density and temperature of the liquid branch of the liquid‐vapor phase boundary of forsterite. This work is combined with previous work constraining pressure, density, temperature, and entropy of the forsterite principal Hugoniot. We find that the vapor curves in previous forsterite equation of state models used in giant impacts vary substantially from our experimental results, and we compare our results to a recently updated equation of state. We have also found that due to under‐predicted entropy production on the principal Hugoniot and elevated temperatures of the liquid vapor phase boundary of these past models, past impact studies may have underestimated vapor production. Furthermore, our results provide experimental support to the idea that giant impacts can transform much of the mantles of rocky planets into supercritical fluids. Plain Language Summary: Collisions onto planets during planet formation can reach extreme pressures and temperatures. Giant impacts, like one that may have made the moon, reach pressures of millions of atmospheres. Decompression from such high pressures causes the material that makes up planets to melt and vaporize. To help predict the post collision structure of planets, we performed laboratory experiments on the mineral forsterite (Mg2SiO4) that recreates the extreme conditions of these collisions. We used the Z Machine, a facility at Sandia National Laboratories that can launch projectiles up to 40 km s−1 (almost 90,000 miles per hour), to measure the properties of forsterite once it has decompressed. We find that previous models of forsterite melting and vaporization do not match the experimental results found here. The results provide experimental support that giant impacts yield planets that may have mantles that are partially supercritical fluids, that behave like liquids and gases. Key Points: We performed reverse impact experiments and shock‐and‐release experiments to probe the density and temperature of the liquid‐vapor phase boundaryThe experimentally determined liquid‐vapor dome does not agree with commonly used equation of state modelsSupercritical post‐impact states are easier to achieve than previously modeled [ABSTRACT FROM AUTHOR]

Collisions that induce melting and vaporization can have a substantial effect on the thermal and geochemical evolution of planets. However, the thermodynamics of major minerals are not well known at the extreme conditions attained during planet formation. We obtained new data at the Sandia Z Machine and use published thermodynamic data for the major mineral forsterite (Mg 2SiO 4) to calculate the specific entropy in the liquid region of the principal Hugoniot. We use our calculated specific entropy of shocked forsterite, and revised entropies for shocked silica, to determine the critical impact velocities for melting or vaporization upon decompression from the shocked state to 1 bar and the triple points, which are near the pressures of the solar nebula. We also demonstrate the importance of the initial temperature on the criteria for vaporization. Applying these results to N‐body simulations of terrestrial planet formation, we find that up to 20% to 40% of the total system mass is processed through collisions with velocities that exceed the criteria for incipient vaporization at the triple point. Vaporizing collisions between small bodies are an important component of terrestrial planet formation. Plain Language Summary: During planet formation, collisions onto planets and between planetary building blocks, such as asteroids, can be fast enough to melt or vaporize rock. Melting and vaporization changes the chemical makeup of planets. However, until recently, the extreme pressures and temperatures reached during planetary collisions could not be reproduced in laboratory experiments. We were missing key measurements on major materials that make up Earth's mantle, such as the mineral forsterite (Mg 2SiO 4). Here, we used the Z Machine, a facility at Sandia National Laboratories that can launch projectiles up to 40 km/s (almost 90,000 miles per hour), to measure the properties of forsterite at extreme conditions. Based on these measurements, we calculated that collisions faster than 8.2 km/s (about 18,000 miles per hour) can completely melt and begin to vaporize the rocky portions of planets and their building blocks. We then analyzed computer simulations of planet formation to determine how much material could have been melted or vaporized during the growth of our rocky planets. We found that 20% to 40% of all the material that makes up the inner solar system could have been involved in collisions that melted and vaporized rock. Key Points: We calculate specific entropy on the principal Hugoniot of forsterite (Mg 2SiO 4) by thermodynamic integration of experimental dataWe derive new criteria for shock‐induced melting and vaporizationVaporizing collisions between small bodies are an important component of terrestrial planet formation [ABSTRACT FROM AUTHOR]

Laser-driven shock compression experiments reveal the presence of a phase transition in MgSi03 over the pressure-temperature range 300-400 GPa and 10000-16 000 K, with a positive Clapeyron slope and a volume change of ∼6.3 (± 2.0) percent. The observations are most readily interpreted as an abrupt liquid-liquid transition in a silicate composition representative of terrestrial planetary mantles, implying potentially significant consequences for the thermal-chemical evolution of extrasolar planetary interiors. In addition, the present results extend the Hugoniot equation of state of MgSi03 single crystal and glass to 950 GPa. [ABSTRACT FROM AUTHOR]

Equation-of-state (pressure, density, temperature, internal energy) and reflectivity measurements on shock-compressed CO2 at and above the insulating-to-conducting transition reveal new insight into the chemistry of simple molecular systems in the warm-dense-matter regime. CO² samples were precompressed in diamond-anvil cells to tune the initial densities from 1.35 g/cm³ (liquid) to 1.74 g/cm³ (solid) at room temperature and were then shock compressed up to 1 TPa and 93 000 K. Variation in initial density was leveraged to infer thermodynamic derivatives including specific heat and Gruneisen coefficient, exposing a complex bonded and moderately ionized state at the most extreme conditions studied. [ABSTRACT FROM AUTHOR]

The short-range structure of liquid carbon dioxide is investigated at pressures (P) up to 10 GPa and temperatures (T) from 300 to 709 K by means of x-ray diffraction experiments in a diamond anvil cell (DAC) and classical molecular dynamics (MD) simulations. The molecular x-ray structure factor could be measured up to 90nm-1 thanks to the use of a multichannel collimator which filters out the large x-ray scattered signal from the diamond anvils. The experimental data show that the short-range structure of fluid CO2 is anisotropic and continuously changes from a low density to a high density form. The MD simulations are used to extract a detailed three-dimensional analysis of the short-range structure over the same P-T range as the experiment. This reveals that upon compression, a fraction of the molecules in the first-neighbor shell change orientation from the (distorted) T shape to the slipped parallel configuration, accounting for the observed structural changes. The local arrangement is found similar to that of the Pa3 solid at low density and to that of the Cmca crystal at high density. The comparison with other simple quadrupolar liquids, either diatomic (I2) or triatomic (CS2), suggests that this structural evolution with density is a general one for these systems. [ABSTRACT FROM AUTHOR]

Equation-of-state (pressure, density, temperature, internal energy) and reflectivity measurements on shock-compressed CO_{2} at and above the insulating-to-conducting transition reveal new insight into the chemistry of simple molecular systems in the warm-dense-matter regime. CO_{2} samples were precompressed in diamond-anvil cells to tune the initial densities from 1.35  g/cm^{3} (liquid) to 1.74  g/cm^{3} (solid) at room temperature and were then shock compressed up to 1 TPa and 93 000 K. Variation in initial density was leveraged to infer thermodynamic derivatives including specific heat and Gruneisen coefficient, exposing a complex bonded and moderately ionized state at the most extreme conditions studied.

This corrects the article DOI: 10.1103/PhysRevLett.108.065701.