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 Us–up 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.

determine the silicate solubility and metal-silicate partitioning behavior of W, including its concomitant oxidation state. However, results of previous studies (Fig. 1) are inconsistent on whether W occurs as W4+ or W{sup 6+}. It is assumed that W{sup 4+} is the cation valence relevant to core formation. Given the sensitivity to silicate composition of high valence cations, knowledge of the oxidation state of W over a wide range of fO{sub 2} is critical to understanding the oxidation state of the mantle and core formation processes. This study seeks to measure the W valence and change in valence state over the range of fO{sub 2} most relevant to core formation, around IW-2.

Mechanical equation-of-state data of initially liquid and solid CO2 shock-compressed to terapascal conditions are reported. Diamond-sapphire anvil cells were used to vary the initial density and state of CO2 samples that were then further compressed with laser-driven shock waves, resulting in a data set from which precise derivative quantities, including Grüneisen parameter and sound speed, are determined. Reshock states are measured to 800 GPa and map the same pressure-density conditions as the single shock using different thermodynamic paths. The compressibility data reported here do not support current density-functional-theory calculations, but are better represented by tabular equation-of-state models.

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.

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 ((Mg 0.91 Fe 0.09 ) 2 SiO 4 ) 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 (Mg 2 SiO 4 ), the presence of Fe in typical mantle abundance (∼9 wt% FeO) alters the U S ‐ u P 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).

Introduction: Planet formation and evolution involves high energy impacts capable of melting and vaporizing silicate mantles [1, 2]. SiO2 is an important end-member phase and reference material. At present, researchers lack a wide-ranging equation of state model for SiO2 that accurately captures the temperatures on the shock Hugoniot and post-shock states. The quartz and fused silica (amorphous SiO2) equations of state (EOS) can be improved with additional lab data, particularly in situ shock and post-shock temperatures in the region where these materials undergo shock melting. Along with their utility as compositional endmember minerals, these materials are often used in a variety of shock experiments as windows and standards for impedance matching and thermal emission [3, 4]. Thus, improving the laboratory measurements and modeled data for these materials provides better standard references. Previous studies using gas guns [5, 6] and laserdriven shocks [3] sampled this region, but little data is available in the superheating region of the Hugoniot and liquid region along the vapor curve. Additional data in this region provides insight to both the transition of SiO2 into the liquid phase in a shocked state as well as the onset of melting and vaporization upon release. The analytic equations of state code package (ANEOS) is frequently used by the planetary science community as it is capable of spanning the substantial temperature and pressure range achieved in natural impact phenomenon [7]. The code package has multiple features that enable modeling of solids, liquids, gases and plasmas. For most natural materials, the code package cannot accurately model the entire pressuretemperature range needed. As a result, each developer must make decisions about which features to use in the code package and which regions to fit more accurately. These decisions lead to a set of material parameters for use with a specific version of the ANEOS code that are constrained by data in some regions of phase space. Melosh [7] made updates to ANEOS using SiO2 where a Mie-type potential is used for the solid phase and molecular clusters are used for the vapor phase (M-ANEOS). At present, the available ANEOS models for silica have significant discrepancies in the melt region and liquidvapor phase boundary compared to laboratory observations. Figure 1 shows currently available ANEOS model Hugoniot and vapor domes for SiO2 alongside lab data [6, 11, 8]. This study focuses on taking shock and post-shock temperatures of quartz and fused silica in the pressure range where these materials undergo superheating and melting, approximately 55-130 GPa using multiple pyrometry systems. Here, we describe our shock pyrometry experiments on fused silica as well as plans for improving the model equation of state.

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 pre-compressed 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.

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 (Mg2SiO4) 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 (Mg2SiO4). 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.

Here we describe the implementation and calibration of a streaked visible spectrometer (SVS) for optical pyrometry and emission/absorption spectroscopy on light gas gun platforms in the UC Davis Shock Compression Laboratory. The diagnostic consists of an optical streak camera coupled to a spectrometer to provide temporally and spectrally-resolved records of visible emission from dynamically-compressed materials. Fiber optic coupling to the sample enables a small diagnostic footprint on the target face and flexibility of operation on multiple launch systems without the need for open optics. We present the details of calibration (time, wavelength and spectral radiance) for absolute temperature determination and present benchmark measurements of system performance.

Forsterite (Mg 2 SiO 4 ) single crystals were shock compressed to pressures between 200 and 950 GPa using independent plate‐impact steady shocks and laser‐driven decaying shock compression experiments. Additionally, we performed density functional theory‐based molecular dynamics to aid interpretation of the experimental data and to investigate possible phase transformations and phase separations along the Hugoniot. We show that the experimentally obtained Hugoniot cannot distinguish between a pure liquid Mg 2 SiO 4 and an assemblage of solid MgO plus liquid magnesium silicate. The measured reflectivity is nonzero and increases with pressure, which implies that the liquid is a poor electrical conductor at low pressures and that the conductivity increases with pressure.

Recent discoveries of terrestrial exoplanets distant from our solar system motivate laboratory experiments that provide insight into their formation and thermal evolution. Using laser-driven shock wave experiments, we constrain high-temperature and high-pressure adiabats and the equation of state of ${\mathrm{MgSiO}}_{3}$, a dominant mantle constituent of terrestrial exoplanets. Critical to the development of a habitable exoplanet is the early thermal history, specifically the formation and freezing of the magma ocean and its role in enabling convection in the mantle and core. We measure the adiabatic sound speed and constrain the melt transition along the Hugoniot and find that the adiabats and melt boundary of silicate magmas are shallower than predicted. This suggests that small changes in the temperature of a super-Earth mantle would result in rapid melting and solidification of nearly the entire mantle.

D. E. Bliss, D. E. Fratanduono, R. G. Kraus, M. Millot, D. K. Spaulding, L. Shulenburger, S. T. Stewart, and S. B. Jacobsen, Sandia National Laboratories, Albuquerque, NM, USA, sroot@sandia.gov; Department of Earth and Planetary Sciences, U. of California, Davis, CA, USA. Lawrence Livermore National Laboratory, Livermore CA, USA. Department of Earth and Planetary Sciences, Harvard University, Cambridge, MA, USA.

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