FeO (wüstite), which exhibits complex electronic and structural properties with increasing pressure and temperature, is a key mineralogical phase for understanding deep planetary interiors. However, direct measurements of its spin state at high-pressure and temperature remain challenging in static compression experiments. Here, we employ laser-driven shock compression to extend the FeO principal Hugoniot up to ∼900 GPa and perform in situ X-ray diffraction and X-ray emission spectroscopy up to 250 GPa, probing FeO's crystal structure and spin state. We demonstrate a continuous spin crossover of iron in FeO over a broad pressure range, with the high-spin state persisting beyond Earth's core-mantle boundary (CMB) conditions. These observations provide new experimental constraints on iron spin state at extreme conditions essential for geophysical models of (exo)planetary interiors.

Meteorites suggest the Martian core comprises iron (Fe) or iron-nickel (Fe-Ni) alloy with sulfur (S) identified as the primary light element. The InSight data revealed a larger, less dense Martian core than previously estimated, indicating additional light elements. Recent studies have considered hydrogen (H) as a light element candidate for the Martian core. However, the co-alloying behaviors of S and H in Fe metal at the Martian core conditions are not well understood. This study investigates the influences of H and its amount on phase relations in the Fe-S systems under the pressure-temperature conditions relevant to the Mars core in laser- heated diamond-anvil cells. We found that hydrogen destabilizes Fe3S. At low S and H contents upon melting, the Fe-S-H ternary produces H-rich metallic liquid coexisting with S-rich solid alloy phase. Stable solidus phase changes from Fe2S to FeS to FeSxHy with an increase in H-2 content in the medium from 0.06 to 0.18 to 0.33 wt%. The cotectic line inferred from our data is located close to the S (13-15 wt%) and H (<2 wt%) contents considered geochemically plausible for Mars. The observation provides a compelling explanation for the possible difference in light element composition between the molten Martian outer core and the recently found solid inner core inferred from geophysical observations. This study sheds light on the interplay of S and H for Fe metal, offering important insights for possible core mineralogy for Mars and sub-Earth rocky exoplanets across various scenarios for the H and S contents.

The incorporation of magnesium (Mg) into early planetary cores has been proposed as a source of compositional buoyancy through subsequent MgO precipitation. In the dissociation framework, Mg partitions independently of oxygen (O) into liquid Fe metal alloy, making the precipitation sensitive to the Mg budget. This study investigates the effect of silicon (Si), an important light element in the planetary cores, on the alloying behavior of Mg in iron (Fe) metal under high-pressure and high-temperature conditions. Using laser-heated diamond anvil cells and synchrotron X-ray diffraction, we observed the formation of -type MgFeSi at pressures below 25 GPa and 2000 K. At pressures above 50 GPa, Mg is found to be incorporated into the B2 phase of FeSi and Fe-16Si, with a concentration of approximately 8 atom% (at.%) in FeSi and 5-10 at.% in Fe-16Si. Compared with the nearly immiscible Fe-Mg binary under ambient conditions and only about 4 at.% Mg in Fe metal reported around 20 GPa in previous studies, our results demonstrate that Si can enhance Mg incorporation in Fe-rich alloys at lower pressures (therefore in smaller rocky planets), while in the stability field of bcc Mg alloyed amount appears to remain at least similar between Si-bearing and Si-free cases (therefore in larger rocky planets). Our result indicates that Mg can be an important light element (a few at.%) in the solid part of Fe metal-rich cores if Si is present in the system.

Geophysical detection of subducted mid-ocean ridge basalt (MORB) in the lower mantle is hindered by uncertainties in the elasticity of Fe,Al,Mg,Ti-bearing davemaoite, a key MORB component. Using Brillouin spectroscopy and x-ray diffraction, we determined the elasticity of a Ca0.906(1)Fe2+0.027(1)Fe3+0.042(1)Mg0.033(1)Al0.072(1)Ti0.020(1)Si0.912(1)O3 davemaoite up to 113 gigapascals and 2294 K. We found that it exhibited a shear wave velocity 10 to 20% slower than end-member davemaoite, making it the slowest phase among major lower-mantle minerals. Our models show that MORB, containing 20 to 25 volume percent davemaoite, potentially contributes to large low-shear-velocity provinces (LLSVPs), whereas a cumulate layer enriched in davemaoite crystallized from basal magma ocean may comprise ultralow-velocity zones (ULVZs). Davemaoite's ability to host incompatible and heat-producing elements possibly links LLSVPs and ULVZs to mantle plume initiation and geochemical signatures of ocean island basalts.

Iron(Fe)-water reactions in a magma ocean can influence water storage and density of planets. These reactions can form Fe-O-H phases, whose density, melting, and electronic properties at planetary interior conditions are important for informing planetary models. Here, we study natural goethite (α-FeOOH) that is shock-compressed along its principal Hugoniot. Analysis of our velocity interferometer system for any reflector (VISAR) results extends the equation of state to over 800 GPa. X-ray diffraction and VISAR reflectivity results indicate the onset of melting occurs at 95 GPa with complete melting by 166 GPa, which may be relevant to low seismic velocity anomalies observed above the core-mantle boundary. Analysis of X-ray emission spectroscopy results up to 285 GPa shows the spin crossover of Fe, with dominantly low spin Fe above 265 GPa in the melt, supporting formation of dense basal magma oceans in terrestrial planets. Using our measured FeOOH densities, we model planetary interiors up to 10 Earth masses. Assuming FeOOH forms via iron-water reactions, the radius decreases by up to 28

Nitrogen (N) is extremely depleted in the bulk silicate Earth (BSE). However, whether the silicate magma ocean was as N-poor as the present-day BSE is unknown. We performed multi-anvil experiments at 20 GPa and 1,673-2,073 K to determine the dihedral angle of Fe-Ni-N alloy melt in ringwoodite matrix to investigate whether percolation of Fe-rich alloy melt in the solid mantle can explain N depletion in the BSE. The dihedral angles ranged from 112 degrees to 137 degrees, surpassing the wetting boundary. Our experiments suggest that N removal from the mantle by percolation of Fe-rich alloy melt to the Earth's core is unlikely. Therefore, besides N loss to space during planetesimal and planetary differentiation, as well as its segregation into the Earth core, the stranded Fe-rich metal in the deep mantle could be a hidden N reservoir, contributing to the anomalous depletion of N in the observable BSE. Understanding how and when the present-day inventory of nitrogen (N) in the bulk silicate Earth (BSE) was established is important to gain insights into Earth's habitability. A key question remains as to why N is strongly depleted in the BSE than carbon and hydrogen. Efficient segregation of N into the metallic core in the final stage of Earth's formation is postulated to be one of the primary causes behind this depletion. However, it is not clear whether the silicate magma ocean (MO) was as depleted in N as the present-day BSE due to the uncertainties in the degree of metal-silicate equilibration during the final stages of Earth's formation. Post-MO crystallization, Fe-Ni alloy precipitated in the reduced mantle owing to the disproportionation of ferrous iron. We used high-pressure experiments to examine whether this Fe-Ni alloy melt can trap the excess N and percolate through the solid mantle to the core. Our experiments show that the percolation of Fe-Ni-N melt is unlikely owing to its dihedral angle in silicate phases being larger than the wetting boundary. Instead, the Fe-Ni-N alloy stranded in the mantle can be a hidden N reservoir and the present-day BSE may not be as N-depleted as predicted. Dihedral angles of Fe-Ni-N melt in ringwoodite matrix ranged from 112 degrees to 137 degrees, surpassing the wetting boundary Percolation of Fe-Ni-N melt through the solid mantle cannot explain N depletion in the bulk silicate Earth Fe-Ni-N alloy can be a hidden N reservoir in the mantle if excess N was present in the Earth's mantle post core-mantle differentiation

Molten silicates existing at depth play an important role in planetary evolution. Yet, understanding the local structure and properties of liquid silicates under extreme pressure and temperature remains challenging due to the inherent complexities of experimental measurements in such conditions and to the theoretical challenges caused to atomistic simulations by the description of Fe atom behavior. In this presentation, we will show recent results obtained by coupling laser-driven dynamic compression to in situ X-ray probes at the MEC end-station of LCLS at SLAC (Menlo Park, CA, USA) and at the ID24-HPLF instrument at the ESRF (Grenoble, France). The combination of the ultrabright X-ray sources and high-power optical lasers allowed us to probe the local atomic arrangement, spin-state and insights on the electronic structure of shock compressed liquid (Mg,Fe)SiO3 and other Fe-bearing compositions up to 400 GPa along their Hugoniot.

Ultra-low velocity zones (ULVZs) are anomalous structures, generally associated with decreased seismic velocity and sometimes an increase in density, that have been detected in some locations atop the Earth's core-mantle boundary (CMB). A wide range of ULVZ characteristics have been reported by previous studies, leading to many questions regarding their origins. The lowermost mantle beneath Antarctica and surrounding areas is not located near currently active regions of mantle upwelling or downwelling, making it a unique environment in which to study the sources of ULVZs; however, seismic sampling of this portion of the CMB has been sparse. Here, we examine core-reflected PcP waveforms recorded by seismic stations across Antarctica using a double-array stacking technique to further elucidate ULVZ structure beneath the southern hemisphere. Our results show widespread, variable ULVZs, some of which can be robustly modeled with 1-D synthetics; however, others are more complex, which may reflect 2-D or 3-D ULVZ structure and/or ULVZs with internal velocity variability. Our findings are consistent with the concept that ULVZs can be largely explained by variable accumulations of subducted oceanic crust along the CMB. Partial melting of subducted crust and other, hydrous subducted materials may also contribute to ULVZ variability. Earth's core-mantle boundary (CMB), the interface between the solid silicate mantle and the molten iron-rich outer core, is associated with a range of anomalous structures, including ultra-low velocity zones (ULVZs). While generally associated with reduced seismic wave velocities and sometimes increased density, prior studies have reported a wide range of ULVZ characteristics, leading to many questions regarding their origins. The lowermost mantle beneath the southern hemisphere provides a unique environment to study ULVZs because it is located away from regions of large-scale mantle upwelling and downwelling. Our study uses core reflected P-waves (PcP) recorded by seismic stations in Antarctica to investigate this portion of the CMB for ULVZ presence. We find widespread evidence for variable ULVZ structure. Some of the imaged ULVZs can be modeled with a single layer, but others are more complex. We suggest that the ULVZs beneath the southern hemisphere are predominantly associated with subducted oceanic crust that has variable accumulations along the CMB. In some regions, hydrated subducted materials may also experience partial melting, which may contribute to the complicated ULVZ structures imaged in some locations. Core-reflected P-waves are used to investigate ultra-low velocity zones in the lowermost mantle beneath the southern hemisphere Results show widespread evidence for variable ultra-low velocity zones, some of which may indicate layered or gradational structure Variable accumulations of subducted oceanic crust with localized partial melting can explain these anomalous structures

Molten silicates at depth are crucial for planetary evolution, yet their local structure and physical properties under extreme conditions remain elusive due to experimental challenges. In this study, we utilize in situ X-ray diffraction (XRD) at the Matter in Extreme Conditions (MEC) end-station of the Linear Coherent Linac Source (LCLS) at SLAC National Accelerator Laboratory to investigate liquid silicates. Using an ultrabright X-ray source and a high-power optical laser, we probed the local atomic arrangement of shock-compressed liquid (Mg,Fe)SiO3 with varying Fe content, at pressures from 81(9) to 385(40) GPa. We compared these findings to ab initio molecular dynamics simulations under similar conditions. Results indicate continuous densification of the O-O and Mg-Si networks beyond Earth’s interior pressure range, potentially altering melt properties at extreme conditions. This could have significant implications for early planetary evolution, leading to notable differences in differentiation processes between smaller rocky planets, such as Earth and Venus, and super-Earths, which are exoplanets with masses nearly three times that of Earth. Combining laser-driven shock compression and ultra-short X-ray pulses from LCLS, the local structure of liquid silicates was determined up to 385 GPa. Compared with molecular dynamics calculations, continuous densification of O-O and Mg-Si networks may alter melt properties and impact planetary differentiation.

The Earth’s core–mantle boundary presents a dramatic change in materials, from silicate to metal. While little is known about chemical interactions between them, a thin layer with a lower velocity has been proposed at the topmost outer core (Eʹ layer) that is difficult to explain with a change in concentration of a single light element. Here we perform high-temperature and -pressure laser-heated diamond-anvil cell experiments and report the formation of SiO2 and FeHx from a reaction between water from hydrous minerals and Fe–Si alloys at the pressure–temperature conditions relevant to the Earth’s core–mantle boundary. We suggest that, if water has been delivered to the core–mantle boundary by subduction, this reaction could enable exchange of hydrogen and silicon between the mantle and the core. The resulting H-rich, Si-deficient layer formed at the topmost core would have a lower density, stabilizing chemical stratification at the top of the core, and a lower velocity. We suggest that such chemical exchange between the core and mantle over gigayears of deep transport of water may have contributed to the formation of the putative Eʹ layer. Deeply subducted water may have enabled the exchange of hydrogen and silicon between the mantle and core, according to high-pressure and -temperature experiments.

Hexagonal close‐packed (hcp) structured Fe‐Ni alloy is believed to be the dominant phase in the Earth's inner core. This phase is expected to contain 4%–5% light elements, such as Si and H. While the effects of individual light element candidates on the equation of state (EoS) of the hcp Fe metal have been studied, their combined effects remain largely unexplored. In this study, we report the equations of state for two hcp‐structured Fe‐Si‐H alloys, namely Fe0.83Si0.17H0.07 and Fe0.83Si0.17H0.46, using synchrotron X‐ray diffraction measurements up to 125 GPa at 300 K. These alloys were synthesized by cold compression of Fe‐9wt%Si in either pure H2 or Ar‐H2 mixture medium in diamond‐anvil cells. The volume increase caused by a H atom in hcp Fe‐Si‐H alloys is approximately eight times greater than that by a Si atom. We used the improved data set to develop a composition‐dependent EoS that covers a wide range of compositions. Our calculated density and bulk sound velocity of hcp Fe‐Si‐H alloys suggest a large trade‐off between Si and H contents in fitting the seismic properties of the inner core. Combining our new EoS with geophysical and geochemical constraints, we propose 1.6–3 wt% Si and 0.15–0.6 wt% H in the Earth's inner core.

Sub-Neptune exoplanets may have thick hydrogen envelopes and therefore develop a high-pressure interface between hydrogen and the underlying silicates/metals. Some sub-Neptunes may convert to super-Earths via massive gas loss. If hydrogen chemically reacts with oxides and metals at high pressures and temperatures (P−T), it could impact the structure and composition of the cores and atmospheres of sub-Neptunes and super-Earths. While H2 gas is a strong reducing agent at low pressures, the behavior of hydrogen is unknown at the P−T expected for sub-Neptunes’ interiors, where hydrogen is a dense supercritical fluid. Here we report experimental results of reactions between ferrous/ferric oxides and hydrogen at 20–40 GPa and 1000–4000 K utilizing the pulsed laser-heated diamond-anvil cell combined with synchrotron X-ray diffraction. Under these conditions, hydrogen spontaneously strips iron off the oxides, forming Fe-H alloys and releasing oxygen to the hydrogen medium. In a planetary context where this reaction may occur, the Fe-H alloy may sink to the metallic part of the core, while released oxygen may stabilize as water in the silicate layer, providing a mechanism to ingas hydrogen to the deep interiors of sub-Neptunes. Water produced from the redox reaction can also partition to the atmosphere of sub-Neptunes, which has important implications for understanding the composition of their atmospheres. In addition, super-Earths converted from sub-Neptunes may contain a large amount of hydrogen and water in their interiors (at least a few wt% H2O). This is distinct from smaller rocky planets, which were formed relatively dry (likely a few hundredths wt% H2O).

The mechanisms underlying ETS-driven prostate cancer initiation and progression remain poorly understood due to a lack of model systems that recapitulate this phenotype. We generated a genetically engineered mouse with prostate-specific expression of the ETS factor, ETV4, at lower and higher protein dosage through mutation of its degron. Lower-level expression of ETV4 caused mild luminal cell expansion without histologic abnormalities, and higher-level expression of stabilized ETV4 caused prostatic intraepithelial neoplasia (mPIN) with 100% penetrance within 1 week. Tumor progression was limited by p53-mediated senescence and Trp53 deletion cooperated with stabilized ETV4. The neoplastic cells expressed differentiation markers such as Nkx3.1 recapitulating luminal gene expression features of untreated human prostate cancer. Single-cell and bulk RNA sequencing showed that stabilized ETV4 induced a previously unidentified luminal-derived expression cluster with signatures of cell cycle, senescence, and epithelial-to-mesenchymal transition. These data suggest that ETS overexpression alone, at sufficient dosage, can initiate prostate neoplasia.

Many sub-Neptune exoplanets have been believed to be composed of a thick hydrogen-dominated atmosphere and a high-temperature heavier-element-dominant core. From an assumption that there is no chemical reaction between hydrogen and silicates/metals at the atmosphere-interior boundary, the cores of sub-Neptunes have been modeled with molten silicates and metals (magma) in previous studies. In large sub-Neptunes, pressure at the atmosphere-magma boundary can reach tens of gigapascals where hydrogen is a dense liquid. A recent experiment showed that hydrogen can induce the reduction of Fe^2+ in (Mg,Fe)O to Fe^0 metal at the pressure-temperature conditions relevant to the atmosphere-interior boundary. However, it is unclear if Mg, one of the abundant heavy elements in the planetary interiors, remains oxidized or can be reduced by H. Our experiments in the laser-heated diamond-anvil cell found that heating of MgO + Fe to 3500-4900 K (close to or above their melting temperatures) in a H medium leads to the formation of Mg_2FeH_6 and H_2O at 8-13 GPa. At 26-29 GPa, the behavior of the system changes, and Mg-H in an H fluid and H_2O were detected with separate FeH_x. The observations indicate the dissociation of the Mg-O bond by H and subsequent production of hydride and water. Therefore, the atmosphere-magma interaction can lead to a fundamentally different mineralogy for sub-Neptune exoplanets compared with rocky planets. The change in the chemical reaction at the higher pressures can also affect the size demographics (i.e., "radius cliff") and the atmosphere chemistry of sub-Neptune exoplanets.

Although high pressure enables alloying between hydrogen and iron, hydrogen-to-iron molar ratio (H/Fe) so far found in experiments is mostly limited to 1 in the close-packed iron metal under high pressure. We report a H/(Fe + Ni) ratio of 1.8 +/- 0.1 from (Fe,Ni)H-x (or x >= 1.8) quenched from liquid, exceeding the amounts so far reported for densely packed Fe alloys. From the metastable behavior of the frozen (Fe,Ni)H-x liquid during decompression, we infer that the amount is a lower bound and therefore even a greater amount of H can be dissolved in the liquid part of Fe-rich cores of planets. The significant H storage capacity of liquid Fe-Ni alloy is important to consider for potential storage of H in the interiors of low-density planets as well as rocky planets.

Ultralow velocity zones (ULVZs) are the most anomalous structures within the Earth’s interior; however, given the wide range of associated characteristics (thickness and composition) reported by previous studies, the origins of ULVZs have been debated for decades. Using a recently developed seismic analysis approach, we find widespread, variable ULVZs along the core-mantle boundary (CMB) beneath a largely unsampled portion of the Southern Hemisphere. Our study region is not beneath current or recent subduction zones, but our mantle convection simulations demonstrate how heterogeneous accumulations of previously subducted materials could form on the CMB and explain our seismic observations. We further show that subducted materials can be globally distributed throughout the lowermost mantle with variable concentrations. These subducted materials, advected along the CMB, can provide an explanation for the distribution and range of reported ULVZ properties.

Seismic studies have found fine-scale anomalies at the core-mantle boundary (CMB), such as ultralow velocity zones (ULVZs)(1,2) and the core rigidity zone(3,4). ULVZs have been attributed to mantle-related processes(5-10), but little is known about a possible core origin. The precipitation of light elements in the outer core has been proposed to explain the core rigidity zone(3), but it remains unclear what processes can lead to such precipitation. Despite its importance for the outer core(11), the melting behaviour of Fe-Si-H at relevant pressure-temperature conditions is not well understood. Here we report observations of the crystallization of B2 FeSi from Fe-9wt%Si melted in the presence of hydrogen up to 125 GPa and 3,700 K by using laser-heated diamond anvil cells. Hydrogen dramatically increases the Si concentration in the B2 crystals to a molar ratio of Si:Fe approximate to 1, whereas it mostly remains in the coexisting Fe liquid. The high Si content in the B2 phase makes it stable in a solid form at the outermost core temperatures and less dense than the surrounding liquids. Consequently, the Si-rich crystallites could form, float and be sedimented to the underside of the CMB interface, and that well explains the core side rigidity anomalies(3,4). If a small amount of the FeSi crystals can be incorporated into the mantle, they would form dense low-velocity structures above the CMB, which may account for some ULVZs(10). The B-2 FeSi precipitation promoted by H in the outermost core provides a single core-driven origin for two types of anomalies at the CMB. Such a scenario could also explain the core-like tungsten isotope signatures in ocean island basalts(12), after the materials equilibrated with the precipitates are entrained to the uppermost mantle by the mantle plumes connected to ULVZs.

The spin state of Fe can alter the key physical properties of silicate melts, affecting the early differentiation and the dynamic stability of the melts in the deep rocky planets. The low-spin state of Fe can increase the affinity of Fe for the melt over the solid phases and the electrical conductivity of melt at high pressures. However, the spin state of Fe has never been measured in dense silicate melts due to experimental challenges. We report detection of dominantly low-spin Fe in dynamically compressed olivine melt at 150 to 256 gigapascals and 3000 to 6000 kelvin using laser-driven shock wave compression combined with femtosecond x-ray diffraction and x-ray emission spectroscopy using an x-ray free electron laser. The observation of dominantly low-spin Fe supports gravitationally stable melt in the deep mantle and generation of a dynamo from the silicate melt portion of rocky planets.