Recent advances in experimental and computational techniques now allow access to an unprecedented range of conditions relevant to planetary interiors. Static compression experiments with diamond anvil cells reach pressures in the megabar regime, while dynamic compression with free-electron lasers enables ultrafast measurements at extreme conditions relevant to large exoplanets—opening unique opportunities to capture transformations of matter linked to planetary evolution. Complementary computational methods, from ab initio simulations to large-scale geodynamical models, provide key insights to predict the properties of matter at depth and link them to observable planetary parameters such as seismic velocities, mass–radius relationships, or interior dynamics.
This session invites contributions from across planetary sciences that advance our understanding of materials and processes under extreme conditions. We particularly welcome studies addressing mineral physics properties, interior structure and dynamics, and the chemical and physical evolution of Earth and exoplanets. Abstracts highlighting novel experimental techniques, innovative synchrotron and FEL approaches, and cutting-edge modeling methods can all come together to reveal the complex interplay of chemistry, physics, and dynamics within Earth and planetary interiors.
Highly siderophile elements (HSEs) are those with such a strong affinity for iron metal that they are expected to be nearly completely removed from the bulk silicate Earth (BSE) during core formation. Their presence in the BSE today in higher-than-expected absolute abundances and chondritic relative abundances is taken as evidence of late accretion, the addition of the final ~0.5–1% of Earth’s mass after core formation ceased. However, the behaviors of most HSEs have not been studied to the extreme conditions of Earth’s core formation. Here we present new experiments on the metal–silicate partitioning of Pd, Pt, Ru, and Rh to >40 GPa and >4000 K. All of these HSEs become significantly less siderophile at these conditions, to such an extent that core formation ought to leave too much of these elements in the BSE. We will discuss implications for the absolute and relative abundances of HSEs and various processes that can help reconcile their observed values.
How to cite: Fischer, R., Sheehan, J., Suer, T.-A., Gu, J., Bullock, E., Akey, A., Lee, K., Walter, M., and Dong, J.: Metal–silicate partitioning of highly siderophile elements during Earth's core formation, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-22044, https://doi.org/10.5194/egusphere-egu26-22044, 2026.
Space missions, along with ground-based observations, are providing unprecedented geophysical data regarding the interiors of the telluric planets in the solar system. Results from the Insight lander mission indicate that Mars has a large core, mostly, if not entirely, molten, composed of an iron alloy rich in light elements. Chemical analysis of Martian meteorites and planetary differentiation models point to sulfur and oxygen as the most abundant light elements in the core. Yet, the phase diagram and the thermo-elastic properties of solid and liquid alloys in the ternary Fe-S-O system under the pressure and temperature conditions of the Martian core remain largely unconstrained.
We thus investigated the Fe-S-O system and its subsystems by performing X-ray diffraction measurements at the PSICHÉ beamline of the SOLEIL synchrotron using laser-heated diamond-anvil cells. Data were collected on FeS and FeO end-members, as well as on alloys in the Fe-O binary and Fe-S-O ternary systems, in the 10-85 GPa range up to 4000 K. The ability to control the shape of the heating laser combined with temperature mapping enabled by the 4-color pyrometry system, ensured homogenous heating and precise temperature determination. Melting was constrained by tracking the appearance and evolution of the diffuse scattering signal typical of liquids, along with parallel assessment of discontinuities in the optical properties of the investigated samples.
In this presentation, we will outline the developed experimental protocol and present the subsolidus phase diagram and melting curves obtained for FeS and FeO as well as the eutectic melting curve for the Fe-O binary system. Preliminary results for the Fe-S-O ternary system will also be shown. Our results will be compared with previous determinations, addressing ongoing controversies and providing a foundation for an improved understanding of the melting relations in the Fe-S-O ternary system under the conditions of the Martian core.
How to cite: Perruchon-Monge, L., Guignot, N., Boccato, S., Morard, G., Andriambariarijaona, L., Blanchard, I., Boulard, É., Canet, L., Chauvigné, P., Libon, L., Parisiades, P., Rodrigo Ramon, J. L., Baptiste, B., Delbes, L., Doisneau, B., Esteve, I., Man, L., Zhao, B., and Antonangeli, D.: Experimental determination of melting relations in Fe-S-O system and its subsystems under Mars’ core conditions, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-15248, https://doi.org/10.5194/egusphere-egu26-15248, 2026.
Understanding heat transport across the core-mantle boundary (CMB) is essential for constraining Earth’s thermal evolution and the dynamics of its magnetic field. Here we quantify the lattice thermal conductivity of key lower-mantle minerals: periclase, bridgmanite, and post-perovskite, under geophysically relevant pressure-temperature-composition (P-T-X) conditions. Our methodology combines the Boltzmann Transport Equation (BTE), Green-Kubo Molecular Dynamics (GKMD), and Non-equilibrium molecular dynamics (NEMD) within a unified, cross-validated framework that remains robust up to 150 GPa and 4000 K. To extend both accuracy and accessible length and time scales, we incorporate machine-learning interatomic potentials (MLIPs) based on advanced architectures such as MACE, enabling ab initio-quality predictions of phonon-mediated heat transport across strongly anharmonic regimes. We further explore compositional effects in Fe-bearing periclase and observe a pronounced reduction in thermal conductivity for Mg0.75Fe0.25O compare to MgO, highlighting the importance of disorder scattering for deep-mantle heat transport. This ML-accelerated, multi-method approach provides improved constraints on mineral-scale conductivity relevant to CMB heat flux and Earth’s long-term thermal evolution.
How to cite: Tiwari, A. K. and Jahn, S.: Atomic-Scale Investigation of Thermal Conductivity in Lower Mantle Minerals, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-9833, https://doi.org/10.5194/egusphere-egu26-9833, 2026.
The Fe and Al-bearing MgSiO3 bridgmanite is the most predominant mineral in the lower mantle, constituting more than approximately 75% of its volume. Given the lack of direct access to the Earth’s deep interior, the composition and mineralogy of the lower mantle are primarily estimated by comparing compressional- (Vp), and shear-wave velocity (Vs) profiles determined from seismological observations with those calculated for candidate mineral assemblages, under pressure and temperature conditions that correspond to those of the lower mantle. In this study, we conducted ultrasonic interferometry measurements on MgSiO3 and (Mg,Fe)(Si,Al)O3 bridgmanite in a large volume press up to 42 GPa and 1500 K using advanced multi-anvil techniques, towards the conditions of middle lower mantle. This is a radical extension in the conditions at which the high-pressure ultrasonic interferometry technique has been used, and the temperature dependency of bridgmanite’s sound velocity at high pressures has been evaluated with unprecedented accuracy. Using the new data, we constructed an integrated thermoelastic model for bridgmanite, providing improved constraints for interpreting seismological observations and for refining models of lower-mantle composition.
How to cite: Man, L., Pierru, R., Niu, G., Qian, C., Kurnosov, A., Chakraborti, A., Zhou, W., Feng, X., Farla, R., Zhou, C., Liu, Z., Boffa Ballaran, T., and Frost, D.: Ultrasonic Interferometry Measurements on Bridgmanite up to Mid–Lower Mantle Conditions, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-19668, https://doi.org/10.5194/egusphere-egu26-19668, 2026.
Seismic observations of ultra-low velocity zones (ULVZs) at the core-mantle boundary (~2900 km depth) suggest the presence of a dense silicate melt layer at the base of the mantle [1]. Such a layer is commonly interpreted as a remnant basal magma ocean, preserved after metal-silicate differentiation and partial crystallization of the early Earth’s mantle. The existence of a stable melt layer at these extreme conditions has important implications for the chemical stratification of the lowermost mantle, the evolution of mantle convection, and the long-term storage of incompatible elements and volatiles [2],[3]. Geodynamic models and geochemical proxies support the potential for melt retention at the core-mantle boundary, yet the stability of silicate melts remains debated due to their typically lower density relative to surrounding crystalline phases [4]. Resolving this requires quantitative constraints on melt density and structure under lower-mantle pressures.
Experimental data addressing the effect of iron on silicate melt properties at relevant pressures, however, remain sparse because of the challenges associated with probing weakly scattering amorphous materials at extreme conditions. To address this, we conducted in situ synchrotron X-ray diffraction experiments on Fe-bearing silicate glasses of composition (Mg1-xFex)SiO3 (x = 0, 0.1, 0.2, 0.4) up to 135 GPa at the ESRF ID27 beamline. High-energy X-rays (55 keV) combined with an optimized multichannel collimator system [5] allowed data acquisition over an extended Q range, enabling detailed pair distribution function analyses. Mass density indicates a pronounced effect of Fe content above ~20 GPa, while the atomic density remains nearly constant. This is consistent with Fe substituting for Mg in the silicate structure. These observations provide experimental constraints on iron-induced density variations in deep silicate melts, informing models of melt stability at the base of the mantle.
To investigate the effect of volatiles on silicate melt structure and density, a new beamtime is scheduled on ID27 beamline at ESRF in January 2026. Depending on the outcomes, results on CO2- and H2O-enriched silicate glasses in the (Ca,Al,Na,Mg)SiO system will be presented. These experiments aim to provide novel constraints on the structural and density changes induced by volatiles in silicate melts at lower-mantle pressures.
Combined, these studies advance our understanding of the physical and chemical behavior of silicate melts at core-mantle boundary (CMB) conditions, addressing fundamental questions about melt stability and help to model the coupled effects of CO2 and Fe, Mg and Ca at CMB pressures on the silicate glass density. Such constraints are critical for linking geophysical observations, geochemical signatures, and geodynamic models of Earth’s deep interior, providing new insights into the formation and long-term evolution of the basal magma ocean and its role in the Earth’s volatile budget.
References :
[1] Labrosse et al., 2007. Nature, 450(7171), 866 869
[2] Hirose et al., 2002. Physics Of The Earth And Planetary Interiors, 146(1-2), 249-260
[3] Garnero, E. J., et al. (2016). Nature Geoscience, 9(7), 481-489
[4] Dragulet and Stixrude. Geophysical Research Letters, 51(12)
[5] Mezouar et al., 2024. High Pressure Research, 44(3), 171–198
How to cite: Canet, L., Rosa, A., Prescher, C., Otzen, C., Boccato, S., Sossi, P., Libon, L., Lelosq, C., Deguen, R., Gerin, M., Rodriguez, J., Wehinger, B., Pakhomova, A., Hernandez, J.-A., Mijit, E., Mezouar, M., and Morard, G.: The effect of Iron on the structure and density of silicate melts under extreme conditions, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-19233, https://doi.org/10.5194/egusphere-egu26-19233, 2026.
The Earth's mantle has elevated Fe3+ contents relative to those of other telluric bodies, a property thought to reflect the disproportionation of ferrous iron into its metallic and ferric counterparts during core formation. However, how the oxidation and electronic state of iron change as a function of pressure in compositions relevant to that of Earth's mantle are not fully understood. In this study, we present in-situ energy domain synchrotron Mössbauer spectra of 57Fe-enriched peridotitic- and basaltic glasses at 298 K compressed from 1 bar to 174 GPa in a diamond anvil cell. Glasses were synthesised with different Fe3+/[Fe3+ + Fe2+] ratios, 0.02 ± 0.02 and 1.00 ± 0.02, respectively, as determined by colorimetry. At 1 bar, the spectrum of the Fe3+-basaltic glass is well fit by a single doublet. In contrast, the spectra of both Fe2+-rich peridotitic and basaltic glass are fit by two doublets, D1 (~92 %) and D2 (~8 %) at 1 bar. As pressure increases, the integral area of the D2 doublet increases at the expense of D1 to reach a D2/(D1 + D2) ratio of 0.65 by 172 GPa. Because this transition is reversible with pressure and no metallic iron is detected, the D2 feature is ascribed to Fe2+ in its low spin (LS) state, whereas D1 is consistent with Fe2+ high spin (HS). This assignment resolves a long-standing controversy on the interpretation of the Mössbauer spectra of basaltic glasses. As a consequence of the stabilisation of Fe2+ with pressure, terrestrial planets more massive than Earth likely do not host increasingly oxidising mantles.
How to cite: Sossi, P., Girani, A., Petitgirard, S., Yaroslavtsev, S., Aprilis, G., Badro, J., Bézos, A., and St.C. O'Neill, H.: The influence of low-spin ferrous iron on the oxidation state of the Earth's mantle, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-13480, https://doi.org/10.5194/egusphere-egu26-13480, 2026.
Telescopes with higher resolution are enabling humanity to explore and characterize rocky worlds beyond the Solar System. These low-mass exoplanets tend to lose their primordial H2-He atmospheres, and derive secondary atmospheres from outgassing supplied by silicate mantles. The oxidation state of an outgassed atmosphere has broad implications for habitability, and it hinges on the redox state of degassing rocks or melts. Over the past decades, both experimental and modeling studies have pointed out that high pressures stabilize ferric (Fe3+) over ferrous (Fe2+) iron in a magma ocean. This implies that a larger planet with a deeper magma ocean would have a higher Fe3+/Fe2+ ratio, which would lead to a higher mantle oxygen fugacity and thus a more oxidized atmosphere. We synthesize previous experimental and modeling findings into an improved computational tool to explore how a rocky (exo)planet’s interior redox state depends on its size, density, and bulk silicate composition. Our model predictions are testable through future observations of rocky exoplanets.
How to cite: Tian, M. and Heng, K.: Do Larger Rocky Exoplanets Outgas More Oxidized Atmospheres?, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-14407, https://doi.org/10.5194/egusphere-egu26-14407, 2026.
Sub-Neptunes are a category of exoplanets, with radius between 1.75 and 3 Earth radius, sufficiently large to accumulate a thick atmosphere composed mostly by H2 and He on top of a rocky support. Most of the observed Sub-Neptunes orbit around their star in less than 100 days. Based on the relative position to their star and the size of the atmospheres, the temperatures and pressures at the atmosphere/mantle interface could go up to 4000K and 10GPa[1]. At such conditions, their condensed surface should be completely molten creating magma oceans. This magma ocean or magma ponds react with the atmosphere in a way that it can affect the mass and composition of the planets [2]. Such interactions forge the mass-radius relation.
Here, we use ab-initio molecular dynamics to study the chemical exchanges between magma ocean and atmosphere. These exchanges consist of outgassing, dissolution of volatiles into the magma, and redox reactions [3]. We focus on the redox reactions mediated by the presence of Fe. We work on two extremes systems: Fe + H2O and FeO + H2. We monitor the chemical reactions between the different phases present in our systems, the oxidation state of iron and finally the catalytic role of Fe. Our simulations show that Fe is a catalyst for H2O dissociation of the Fe + H2O systems, and a H2O generator in FeO + H2 systems. The immiscibility gap is closed at 4000K for chemical systems at all pressures.
How to cite: Andronaco, M.: Dissolution of gases in magma oceans on Sub-Neptunes, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-7054, https://doi.org/10.5194/egusphere-egu26-7054, 2026.
This study presents a comprehensive first-principles investigation of the pressure-dependent phase transitions and elastic properties of GeO2. Using density functional theory, complete sets of single-crystal elastic constants were calculated at 0 K for all structurally stable phases over a wide pressure range (0 -120 GPa). Strain analysis identifies the rutile-to-CaCl2 type transition at a critical pressure of 14.57 GPa (Ghosh et al., 2025). Moreover, this transition is a second-order phase transition. Within the framework of classical Landau theory, this transition is described by symmetry-adapted strain order parameters. We have also shown the evolution of elastic moduli with pressure using Landau coefficients obtained from the parent tetragonal phase (rutile). The results show elastic softening as the critical pressure is approached, manifested by clear anomalies in the bulk modulus and compressional wave velocity (Vp), both of which exhibit a distinct minimum near the transition pressure. Following this analysis, we have also computed the elastic constants for the α-PbO2 and pyrite-type phases of GeO2. Elastic anisotropy analysis reveals a strong mechanical instability across the tetragonal-to-orthorhombic transition, driven primarily by a rapid reduction in shear wave velocity. These results provide a unified, elastic, and symmetry-based interpretation of pressure-induced phase transitions in GeO2, with implications for understanding the mechanical stability and seismic properties of rutile-type oxides under extreme conditions.
How to cite: Kumar, G., Ghosh, S., Pillai, S. B., and Dutta, R.: High-pressure elastic properties of GeO2 polymorphs up to 120 GPa, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-5107, https://doi.org/10.5194/egusphere-egu26-5107, 2026.
Water and ammonia are of vital importance in planetary science and are regarded as the main constituents of icy giants (Uranus and Neptune) as well as of icy satellites such as Titan, Triton, and the dwarf planet Pluto. In addition, high-pressure ionic phase-transition studies of ammonia and water are particularly crucial for verifying the physical feasibility of the magnetic-field models of icy giants—models in which the field is dominated by a quadrupole term rather than the dipole term seen in other Solar-System planets. Some previous studies have shown that both water ice and ammonia ice undergo ionic phase transitions under high pressure, whereas investigations of the ionic phase-transition behaviour of ammonia–water mixtures at pressures beyond the commonly encountered DMA phase are scarce. In this study, high-pressure Raman scattering and X-ray diffraction are employed to investigate the ionizing phase transitions of ammonia hydrates of different concentration ratios up to 202 GPa, and the transition mechanisms together with their variation with concentration are summarized. The experiments extend high-pressure investigations of ammonia hydrates of different concentrations into a new pressure range, elucidate two phase-transition mechanisms—ionization and hydrogen-bond symmetrization—occurring in ammonia hydrates under high pressure, provide fresh experimental evidence for pressure-driven proton motion, and offer new insights into the study of ionic and superionic phases of the ammonia–water and related mixture systems.
How to cite: Yuan, X., Li, X., and Li, F.: Pressure-induced ionization and hydrogen-bond symmetrization of ammonia hydrates: implications for the magnetic-field architectures of ice giants, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-6389, https://doi.org/10.5194/egusphere-egu26-6389, 2026.
MgO is an important planetary material and computational studies has shown some fascinating mechanical behaviour of this material. At very low strain rates (10-16 /s) and high pressures, the slow diffusion of oxygen impedes dislocation recovery and strengthens MgO dramatically. At high pressures above 50 GPa, a change in deformation mechanism is predicted where the slip system changes from [110](110) to [110](100). Here, we demonstrate the mechanical behaviour of MgO at conditions up to 160 (20) GPa and 2000 (300)K. We use laser shock compression along with ultra-fast diagnostics at the European XFEL to probe how the rapidly changing pressure-temperature conditions affect the dominant deformation mechanisms in polycrystalline MgO. These observations, coupled with elasto-viscoplastic self-consistent (EVPSC) simulations, unequivocally prove that MgO attains plastic regime in the nano-seconds scale which we can then study and model in terms of strength and deformation mechanisms. The experiments point to a rich intricate mechanical behaviour in shocked polycrystalline ceramics for the first time, which may have profound impact on the viscosity and rheological behaviour of Earth and Earth-like exo-planets.
This work is the result of experiments performed under the EuXFEL 6659 community proposals led by J. Eggert and G. Morard.
How to cite: Chakraborti, A., Ginestet, H., Chantel, J., and Merkel, S. and the EuXFEL 6659 community proposal: Ultra-fast visualisation of plasticity in polycrystalline MgO under shock compression, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-7287, https://doi.org/10.5194/egusphere-egu26-7287, 2026.
Iron meteorites preserve key records of early planetary differentiation and core formation processes. However, the combined effects of metal–silicate separation, core crystallization, and subsequent impact modification have produced complex and variable geochemical signatures, complicating efforts to reconstruct their parent-body origins and evolutionary histories. To address this challenge, we compiled a comprehensive geochemical dataset of iron meteorites and developed a process-oriented statistical framework that characterizes iron meteorite geochemistry through element covariation patterns and compares their internal chemical structures across different meteorite groups. The results reveal distinct and internally consistent geochemical structures among major magmatic iron meteorite groups. IIAB and IIIAB irons show strong positive correlations among HSEs and systematic anticorrelations with Ni, consistent with well-developed metal crystallization trends and relatively continuous core differentiation histories. In contrast, IVA and IVB irons exhibit weaker coupling between HSEs and other elements, together with subdued or decoupled Ga–Ge behavior, suggesting more complex or non-equilibrium differentiation pathways. The IID group displays intermediate and less coherent correlation structures, indicating greater heterogeneity in internal processes or parent-body conditions. This process-oriented framework provides a quantitative basis for comparing the internal geochemical architectures of iron meteorite groups and offers new perspectives on the diversity of differentiation histories recorded by metallic planetary cores.
How to cite: Zhou, T., Qiu, K.-F., and Caracas, R.: Element Covariation Reveals Diverse Core Differentiation Histories among Magmatic Iron Meteorites, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-11922, https://doi.org/10.5194/egusphere-egu26-11922, 2026.
The physical properties of silicate melts at temperature and pressure conditions of the Earth’s mantle have a fundamental influence on the chemical and thermal evolution of the Earth. However, direct investigations of melt structures at these conditions are experimentally very difficult or even impossible with current capabilities. To still be able to obtain an estimate of the structural behavior of melts at high pressures and temperatures, amorphous materials have been widely used as analogue materials.
Here we present the structural response of CaSiO3 glass as a proxy for deep mantle melts up to 108 GPa via total X-ray scattering experiments. The measurements were carried out at beamline P02.2 at DESY, Germany, utilizing the newly commissioned Soller Slit configuration. Due to the pronounced size contrast between Ca2+ and Si4+, the Si–O correlations are readily resolved in the pair‐distribution function—something that is impossible in other three component silicate glasses, like MgSiO3 where the Mg–O and Si–O peaks overlap at a larger pressure.
We observe smooth pressure-induced changes in the structure factor and pair distribution function, along with a clear increase in Si–O coordination from four-fold to six-fold within the first 50 GPa. This behavior will be examined in detail, with emphasis on mechanistic differences relative to pure SiO2 and in comparison with other reported results for silicate glasses under similar pressure conditions.
How to cite: Prescher, C., Otzen, C., Cocomazzi, G., Glazyrin, K., and Liermann, H.-P.: Structural changes in CaSiO3 glass up to lower mantle pressures, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-13887, https://doi.org/10.5194/egusphere-egu26-13887, 2026.
Perovskite-structured solids are widely known for their tendency to exhibit rapid oxygen diffusion mediated by vacancy hopping. This has important implications for chemical transport in the deep Earth, given that large portions of the lower mantle are composed of perovskite minerals — bridgmanite (MgSiO3) and davemaoite (CaSiO3). Here, we present a comparative study of extrinsic oxygen diffusion in both minerals using machine learning molecular dynamics simulations. We show that the extended time scales enabled by machine learning potentials allow oxygen diffusion in these materials to be studied with high accuracy, permitting reliable determination of their Arrhenius parameters, namely the pre-exponential factor and activation enthalpy. We discuss differences in these properties between the two minerals in light of their crystal structures. Finally, we consider the broader implications of our diffusion results for chemical exchange and electrical conductivity across distinct mantle reservoirs.
How to cite: Schulze, M. and Steinle-Neumann, G.: Oxygen Diffusion in the Perovskite-Dominated Lower Mantle, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-19831, https://doi.org/10.5194/egusphere-egu26-19831, 2026.
High-pressure ices (ice VI and ice VII) are believed to be the major constituents of the deep interiors of icy satellites and water-rich exoplanets. Incorporation of the impurities is a central problem as it alters the physical and chemical properties of high-P ices and thus influences the interiors of planets. However, the solubility of salt in ice VII remains poorly constrained. Different experiments have reported different estimates. Here, we address this discrepancy from a thermodynamic perspective.
We first developed a machine-learning interatomic potential based on the r²SCAN functional, covering a P-T range of 5–30 GPa and up to 1600 K. The predicted ice VII melting curve matches two recent experimental determinations across the investigated pressure range. Free-energy calculations indicate that the equilibrium solubility of NaCl in ice VII is limited to sub–mol% levels, substantially lower than several previously reported experimental estimates.
Deep-supercooling simulations of homogeneous saline liquids reveal rapid three-dimensional nucleation and growth of ice VII. During this process, the crystallization front advances much faster than solute transport in the liquid, leading to efficient solute trapping and incorporation of salt at concentrations far above the equilibrium limit. We further performed interfacial simulations near solid–liquid coexistence conditions, which show that solute diffusion in the solid remains strongly limited even close to the liquidus.
These results imply that salt retention in high-pressure ice is highly sensitive to the thermodynamic path by which the solid forms. The extremely low diffusivity of salt in the solid also suggests that kinetically produced, supersaturated “salty” high-pressure ice can persist over long timescales at low temperatures.
How to cite: Zhu, X. and Caracas, R.: Thermodynamic and Kinetic Trapping of NaCl in Ice VII, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-5558, https://doi.org/10.5194/egusphere-egu26-5558, 2026.
Simultaneous measurements of acoustic wave velocities and densities of minerals relevant to the Earth’s and other planetary interiors are essential for interpreting seismic observations in terms of possible mineral compositions present at depth. Such combined measurements provide internally consistent data that are independent of external pressure calibrations and can therefore be extrapolated more accurately to conditions that are not yet reachable in the laboratory. However, such measurements at elevated pressures and temperatures are still challenging, especially when using in-house facilities. Here, we present acoustic wave velocities collected for garnet and ringwoodite single crystals with compositions relevant to the Martian mantle, using a Brillouin scattering system coupled with an X-ray diffractometer and a CO₂ laser heating setup.
How to cite: Kurnosov, A., Boffa Ballaran, T., Criniti, G., and Frost, D.: Constraining mineral-physics models of planetary interiors using high-pressure-high-temperature Brillouin scattering measurements, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-14995, https://doi.org/10.5194/egusphere-egu26-14995, 2026.
The Earth’s inner core presents interesting properties such as seismic velocity anisotropy and a complex internal structure that is still under investigation. Establishing the phase diagram of the relevant iron alloys and, first, of pure iron itself is necessary to improve our understanding of planetary cores. The iron phase diagram at high pressure and temperature is still discussed despite numerous experimental and simulation studies. The addition of other elements even complexifies the issue, and, to this day, phase diagrams and melting temperatures of Fe alloys under Earth's core conditions remain to be established.
In this work, we explore the phase diagram of Fe and and Fe-Ni-Si alloy up to over 200 GPa and up to melting through a different thermodynamical pathway from conventional laser-heated diamond anvil cell experiments. The experiments rely on new facilities at the European X-Ray Free-Electron Laser, which provides extremely intense X-ray flashes repeated up to every 220 ns. The facility, coupled with the High Energy Density (HED) instrument, allows heating, melting, and crystallizing iron samples repeatedly and probe for its crystal structure as the sample cools from its previous state.
The first step of the work was to establish the data processing technique and metrology for working on such dataset, which has now been published very recently (Ginestet et al, J Appl Phys, 2026). In this presentation, I will show our latest results on pure Fe and FeNiSi alloys up to pressures on the order of 200 GPa.
How to cite: Merkel, S., Ginestet, H., Zurkowski, C., and Morard, G. and the EuXFEL 3063 and 5700 community proposals: Pure Fe and Fe-Ni-Si alloys under high-pressure and high temperature at the European XFEL, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-13143, https://doi.org/10.5194/egusphere-egu26-13143, 2026.
Posters virtual: Thu, 7 May, 14:00–18:00 | vPoster spot 3
EGU26-4988 | ECS | Posters virtual | VPS25
Adsorption of Helium and Argon on the (001) Surface of Periclase: A First-Principles StudyThu, 07 May, 14:54–14:57 (CEST) vPoster spot 3
The distribution of rare gases within the Earth’s interior has caught the attention of scientists for the past few years. The inertness and volatility of noble gases make them excellent tracers for understanding the chemical evolution of Earth’s mantle and atmosphere. Previous studies indicate that noble gases can be found associated with clathrates, form their own oxides, or, in some cases, noble gases such as helium and xenon can even bond with Fe under extreme pressure (p) - temperature (T) conditions like those in Earth’s core. However, the ability of lower mantle mineral phases to house rare gases remains poorly understood, leaving important gaps in knowledge. Helium and argon are noble gases of interest in this study. The isotopes 4He and 40Ar are produced from the radioactive decay of 238U and 40K within the Earth’s interior, while 3He and 36Ar are regarded as primordial, introduced during the accretion of Earth. Dong et al. (2022) revealed that noble gases can become reactive under mantle pressure conditions. Still, their ability to be incorporated into mantle minerals via adsorption needs to be thoroughly studied, as there are many limitations in the experiments conducted to measure the solubility of noble gases in minerals under mantle p-T conditions. In this study, we investigated the adsorption behavior of helium and argon on the (001) plane of periclase (MgO) by employing first-principles density functional theory (DFT) calculations.
Adsorption energies were estimated across pressures ranging from 0 to 125 GPa, representative of conditions throughout Earth’s interior, i.e., approximately up to the Core Mantle Boundary (CMB). At ambient pressure, both helium and argon showed negative adsorption energies, indicating stable adsorption relative to isolated species (MgO, Ar, He). These energies became increasingly negative with pressure, becoming notably negative beyond 75 GPa which corresponds to lower mantle pressures. This may be due to the accelerated reactivity of noble gases at extreme pressure conditions, as reported in previous studies. Additionally, under all pressure conditions argon exhibited stronger adsorption than helium, indicating enhanced argon retention in lower mantle conditions. However, further investigations into the mechanical and dynamical stability of these adsorbed structures are required to completely understand the mechanisms governing noble gas occurrence in the Earth’s lower mantle.
How to cite: Karangara, A. and Kumar Das, P.: Adsorption of Helium and Argon on the (001) Surface of Periclase: A First-Principles Study, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-4988, https://doi.org/10.5194/egusphere-egu26-4988, 2026.
