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The diffuse scattering signal of amorphous or liquid systems contains information on the local atomic structure, and this can be related to the density, compressibility, thermal expansion and other thermoelastic properties. However, the analysis and full exploitation of the diffuse scattering signal, in particular for systems under extreme conditions of high pressures and temperatures are difficult to handle. Amorpheus is a Python-based software allowing the determination of the structure factor and the radial distribution function of amorphous and liquid systems. Based on previously reported methodologies, Amorpheus stands out for the implementation of automatic algorithms allowing the user to choose the most suitable parameters for the data treatment and making possible systematic analysis of datasets collected in experiments carried out in Paris-Edinburgh press, multi-anvil apparatus or diamond anvil cell. [ABSTRACT FROM AUTHOR]

Mercury's metallic core is expected to have formed under highly reducing conditions, resulting in the presence of significant quantities of silicon alloyed to iron. Here we present the phase diagram of the Fe-FeSi system, reconstructed from in situ X-ray diffraction measurements at pressure and temperature conditions spanning over those expected for Mercury's core, and ex situ chemical analysis of recovered samples. Under high pressure, we do not observe a miscibility gap between the cubic fcc and B2 structures, but rather the formation of a re-entrant bcc phase at temperatures close to melting. Upon melting, the investigated alloys are observed to evolve towards two distinct Fe-rich and Fe-poor liquid compositions at pressures below 35-38 GPa. The evolution of the phase diagram with pressure and temperature prescribes a range of possible core crystallization regimes, with strong dependence on the Si abundance of the core. The iron-silicon phase diagram has been established at the conditions of Mercury's core. The resulting phase diagram is remarkably complex, and presents an array of new mechanisms which may power Mercury's inner dynamo. [ABSTRACT FROM AUTHOR]

The InSight mission to Mars is currently monitoring the seismic activity of the planet. Interpretation of seismological observations in terms of composition and mineralogy requires the knowledge of density and thermo‐elastic properties of constituent materials at pertinent conditions. We thus performed phase equilibria experiments and carried out sound velocity and density measurements on aggregates representative of the Martian mantle over pressures and temperatures directly relevant for Mars' upper and mid mantle. Our results indicate the stability of magnetite, although in a small amount, in phase assemblages at upper mantle conditions, especially in an oxidized environment. The measured pressure and temperature derivatives of compressional and shear velocities show that the temperature‐induced reduction of seismic wave speeds dominates over pressure‐induced effects at Mars' shallow mantle conditions for the predicted areotherms and, independently from mineralogy, support the presence of a low‐shear‐wave‐velocity layer between 150 and 350 km depth, in agreement with seismic observations. Plain Language Summary: The InSight mission operating on Mars is currently monitoring the planet's seismic activity. The recorded marsquakes can be used to obtain information on Mars' internal composition. However, the interpretation of these observations requires knowledge of the physical properties of the minerals expected to compose the Martian mantle at the relevant conditions. In this study we report: (1) experiments investigating the nature and abundance of the mineral phases stable at Martian mantle conditions; (2) sound velocity and density measurements on these rocks over a pressure and temperature range directly relevant for Mars' mantle, providing information that can be directly compared to the seismological findings from the InSight mission. Our results reveal the stability of small amounts of magnetite, an Fe3+‐rich mineral not reported in previous studies but a likely candidate in Mars' oxidized mantle environment. Moreover, measured wave velocities indicate the existence of a region between 150 and 350 km depth where, due to large temperature‐induced reduction, shear wave velocities decrease with depth as opposed to an expected increase. This finding is consistent with recent observations from the InSight mission on Mars. Key Points: Sound wave velocities and density were measured for pressures, temperatures, and mineralogical assemblages representative of Mars' mantleExperimental results support the existence of a low shear velocity layer in the shallow Martian mantlePhase equilibria experiments suggest the existence of ferrian minerals in the oxidized regions of the uppermost Martian mantle [ABSTRACT FROM AUTHOR]

The InSight mission to Mars is currently monitoring the seismic activity of the planet. Interpretation of seismological observations in terms of composition and mineralogy requires the knowledge of density and thermo‐elastic properties of constituent materials at pertinent conditions. We thus performed phase equilibria experiments and carried out sound velocity and density measurements on aggregates representative of the Martian mantle over pressures and temperatures directly relevant for Mars' upper and mid mantle. Our results indicate the stability of magnetite, although in a small amount, in phase assemblages at upper mantle conditions, especially in an oxidized environment. The measured pressure and temperature derivatives of compressional and shear velocities show that the temperature‐induced reduction of seismic wave speeds dominates over pressure‐induced effects at Mars' shallow mantle conditions for the predicted areotherms and, independently from mineralogy, support the presence of a low‐shear‐wave‐velocity layer between 150 and 350 km depth, in agreement with seismic observations. Plain Language Summary: The InSight mission operating on Mars is currently monitoring the planet's seismic activity. The recorded marsquakes can be used to obtain information on Mars' internal composition. However, the interpretation of these observations requires knowledge of the physical properties of the minerals expected to compose the Martian mantle at the relevant conditions. In this study we report: (1) experiments investigating the nature and abundance of the mineral phases stable at Martian mantle conditions; (2) sound velocity and density measurements on these rocks over a pressure and temperature range directly relevant for Mars' mantle, providing information that can be directly compared to the seismological findings from the InSight mission. Our results reveal the stability of small amounts of magnetite, an Fe3+‐rich mineral not reported in previous studies but a likely candidate in Mars' oxidized mantle environment. Moreover, measured wave velocities indicate the existence of a region between 150 and 350 km depth where, due to large temperature‐induced reduction, shear wave velocities decrease with depth as opposed to an expected increase. This finding is consistent with recent observations from the InSight mission on Mars. Key Points: Sound wave velocities and density were measured for pressures, temperatures, and mineralogical assemblages representative of Mars' mantleExperimental results support the existence of a low shear velocity layer in the shallow Martian mantlePhase equilibria experiments suggest the existence of ferrian minerals in the oxidized regions of the uppermost Martian mantle [ABSTRACT FROM AUTHOR]

Si and C are cosmochemically abundant elements soluble in hcp Fe under pressure and temperature and could therefore be present in the Earth's inner core. While recent ab initio calculations suggest that the observed inner core density and velocities could be matched by an Fe‐C‐Si alloy, the combined effect of these two elements has only recently started to be investigated experimentally. We therefore carried out synchrotron X‐ray diffraction measurements of an hcp Fe‐C‐Si alloy with 4 at% C and 3 at% Si, up to ∼150 GPa. Density functional theory calculations were also performed to examine different incorporation mechanisms. These calculations suggest interstitial C to be more stable than substitutional C below ~350 GPa. In our calculations, we also find that the lowest‐energy incorporation mechanism in the investigated pressure range (60–400 GPa) is one where two C atoms occupy one atomic site; however, this is unlikely to be stable at high temperatures. Notably, substitutional C is observed to decrease the volume of the hcp Fe, while interstitial C increases it. This allows us to use experimental and theoretical equations of state to show unambiguously that C in the experimental hcp Fe‐C‐Si alloys is not substitutional, as is often assumed. This is crucial since assuming an incorrect incorporation mechanism in experiments leads to incorrect density determinations of ~4%, undermining attempts to estimate the concentration of C in the inner core. In addition, the agreement between our experiments and calculations supports Si and C as being light elements in the inner core. Key Points: Synchrotron X‐ray diffraction and density functional theory calculations were performed on hcp Fe‐C‐Si alloy with 4 at% C and 3 at% SiDifferent incorporation mechanisms were examined, and the hcp Fe‐C‐Si alloy sample takes the interstitial formAssuming a wrong incorporation mechanism leads to incorrect density determination and a more enhanced density contrast between the alloy and pure Fe [ABSTRACT FROM AUTHOR]

Measurements of ground compliance at the InSight landing site—describing the surface response to pressure loading—are obtained from seismic and meteorological data. Compliance observations show an increase with frequency indicating the presence of a stiffer rock layer beneath the exposed regolith. We performed a Markov chain Monte Carlo inversion to investigate the vertical profile of the elastic parameters down to 20 m below InSight. Compliance was inverted both freely and assuming prior knowledge of compaction in the regolith, and the limitations and strengths of the methods were assessed on the basis of theoretical considerations and synthetic tests. The inverted Young modulus exhibits an increase by a factor of 10–100 over the first 10–15 m, compatible with a structural discontinuity between 0.7 and 7 m. The proposed scheme can be used for joint inversion of other seismic, geological, or mechanical constraints to refine the resulting vertical section. Plain Language Summary: Pressure fluctuations of the Mars' atmosphere induce tiny deformations of the ground that can be measured by the very sensitive seismometer of the InSight mission. The amount of deformation depends on the elastic properties of the sandy regolith (the surface layer exposed and highly fractured by impacts) and of the underlying rocks and can thus be used to explore beneath the surface. In this work, we review the theory describing the ground motion caused by moving pressure perturbations, and we analyze the effect of various parameters (wind speed and layering in the subsurface). We then develop a method to retrieve a vertical profile of the elastic parameters beneath the lander from the measurements. After testing the method on ideal cases, we apply it to data from Mars: The results show that the regolith becomes stiffer with depth and that a layer of harder rock may be present below, with the interface possibly located between 0.7 and 7 depth. Determining the structure of the near surface provides constraints on the geologic history of the landing site and contributes to the explanation of measured seismic signals. Key Points: Ground compliance measurements by InSight depend on the elastic properties in the near surface of MarsObserved compliance from convective vortex encounters and other pressure fluctuations opens the way to the exploration of the near surfaceMarkov chain Monte Carlo inversion for the Young modulus profile suggests stratification within and below the regolith [ABSTRACT FROM AUTHOR]

The elasticity of hcp‐Fe‐5wt%Si has been investigated by synchrotron X‐ray diffraction up to 110 GPa and 2,100 K and by picosecond acoustics measurements at ambient temperature up to 115 GPa. The established Pressure‐Volume‐Temperature equation of state shows that the density of the Earth's inner core can be matched by an Fe‐Si alloy with 5wt% Si for all reasonable core temperatures, but that its compressional and shear velocities remain too high with respect to seismological observations. On the other hand, Fe‐Si alloys whose velocities are expected to get close to seismological observations are too dense at relevant temperatures. Thus, based on these combined velocity‐density measurements, silicon is not likely to be the sole light element in the inner core. Plain Language Summary: Combining measurements of sound velocity and density at high pressures and temperatures shows that while Fe‐5wt% Si can match the density profile of the Earth's inner core, its sound velocity is too high with respect to seismological observations. Key Points: Isothermal compression of Fe‐5wt%Si at high temperatures up to 1.1 Mbar and 2100 KMeasurement of Vp of Fe‐5wt%Si under quasihydrostatic conditions to 1.1 MbarSi cannot be the sole light element in the Earth's inner core [ABSTRACT FROM AUTHOR]

There is a direct relation between the composition of a host star and that of the planets orbiting around it. As such, the recent discovery of stars with unusual chemical composition, notably enriched in carbon instead of oxygen, supports the existence of exoplanets with a chemistry dominated by carbides instead of oxides. Accordingly, several studies have been recently conducted on the Si–C binary system at high pressure and temperature. Nonetheless, the properties of carbides at the pressure‐temperature conditions of exoplanets interiors are still inadequately constrained, effectively hampering reliable planetary modeling. Here we present an in situ X‐ray diffraction study of the Si–C binary system up to 200 GPa and 3,500 K, significantly enlarging the pressure range explored by previous experimental studies. The large amount of collected data allows us to properly investigate the phase diagram and to refine the Clapeyron slope of the transition line from the zinc blende to the rock salt structure. Furthermore, the pressure‐volume‐temperature equation of state is provided for the high‐pressure phase, characterized by low compressibility and thermal expansion. Our results are used to model idealized C‐rich exoplanets of end‐members composition. In particular, we derived mass‐radius relations and performed numerical simulations defining rheological parameters and initial conditions which lead to onset of convection in such SiC planets. We demonstrate that if restrained to silicate‐rich mantle compositions, the interpretation of mass‐radius relations may underestimate the interior diversity of exoplanets. Key Points: We experimentally determined the SiC thermal equation of state up to 200 GPa and 3,500 KWe constrain the SiC B3‐B1 phase transition and expand the Si‐C binary phase diagram mappingCarbon‐enriched planets can have the same mass‐radius relationship as Earth's‐like planets but different dynamical behavior [ABSTRACT FROM AUTHOR]

The density and structure of liquid Fe-C alloys have been measured up to 58 GPa and 3,200 K by in situ X-ray diffraction using a Paris-Edinburgh press and laser-heated diamond anvil cell. Study of the pressure evolution of the local structure inferred by X-ray diffraction measurements is important to understand the compression mechanism of the liquid. Obtained data show that the degree of compression is greater for the first coordination sphere than the second and third coordination spheres. The extrapolation of the measured density suggests that carbon cannot be the only light element alloyed to iron in the Earth's core, as 8-16 at % C (1.8-3.7 wt % C) would be necessary to explain the density deficit of the outer core relative to pure Fe. This concentration is too high to account for outer core velocity. The presence of other light elements (e.g., O, Si, S, and H) is thus required. [ABSTRACT FROM AUTHOR]

We have implemented anin situX-ray diffraction analysis method suitable for the determination of pressure–volume–temperature equations of state in the critical case of liquid and amorphous materials over an extended thermodynamic range (T>2000 K andP>40 GPa). This method is versatile, it can be applied to data obtained using various angle-dispersive X-ray diffraction high pressure apparatus and, contrary toin situX-ray absorption techniques, is independent from the sample geometry. Further advantage is the fast data acquisition (between 10 and 300 s integration time). Information on macroscopic bulk properties (density) and local atomic arrangement (pair distribution functiong(r)) can be gathered in parallel. To illustrate the method, we present studies on liquid Fe–S alloys in the Paris Edinburgh press and in laser-heated diamond anvil cell (DAC), and measurements on Ce glass in DAC at room temperature. [ABSTRACT FROM AUTHOR]

The last decades have witnessed an unprecedented surge in the study of matter and materials at extreme values of pressure and/or temperature. The fundamental importance of this research stems from the fact that high pressure can deeply modify chemical bonds and induce myriad changes in materials. Many breakthroughs have been achieved at synchrotrons worldwide, in fields ranging from earth and planetary sciences to fundamental physics, chemistry, and materials research, and even in the life sciences, where questions on life and biological function under extreme conditions have been studied. [ABSTRACT FROM PUBLISHER]

We performed ultrasonic pulse echo measurements on high-purity polycrystalline cerium across the isostructural γ to α-fcc-to-fcc transition, up to 13 kbar and then back down to 0.3 kbar. Our results confirm the anomalous decrease of the longitudinal sound velocity in the γ-phase approaching the transition, a significant hysteresis loop, and definitively highlight the strong difference in the long wavelength limit of the lattice dynamics of the γ and α phases. We have also studied the kinetics of the transition, which is well described by an Arrhenius behavior, with an activation volume of 10 cm3/mol. [ABSTRACT FROM AUTHOR]

To date, most research utilizing the diamond anvil cell (DAC) at very high pressure has been conducted with polycrystalline samples, thus the results are limited to addressing average bulk properties. However, experiments on single crystals can yield data on a range of orientation-dependent properties such as thermal and electrical conductivity, magnetic susceptibility, elasticity and plasticity. Here, we report new procedures to produce extremely high-quality metallic single crystal samples of size compatible with DAC experiments in the Mbar range. So far, we have produced samples of zinc, Al 2 O 3 , cobalt, molybdenum and cerium, and have evaluated the quality of the finished samples with white-light interferometry, synchrotron X-ray diffraction and inelastic X-ray scattering. [ABSTRACT FROM AUTHOR]

We have used impulsive stimulated light scattering to measure the velocity of an acoustic wave propagating along the interface formed by a cobalt single crystal in contact with liquid helium to a pressure of 10 GPa. We have combined the measured velocities with x-ray diffraction data of cobalt under compression to obtain the elastic tensor elements c44 and c66, and with lower precision c11, c12, and c13. We further show that using published inelastic x-ray scattering results for c33 the associated uncertainties of c11, c12, and c13 are substantially reduced. [ABSTRACT FROM AUTHOR]