Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Geophysical Union (AGU)  

Abstract

The observed large density deficit of the Martian core indicates the presence of large amounts of light elements, and sulfur has been believed to be the dominant one. However, the equation of state (EoS) for liquid Fe‐S has not been well constrained. Earlier experiments examined the liquid Fe‐S density below 8 GPa, much lower than the Mars' core pressure range. Here, the density of liquid FeS was determined based on synchrotron X‐ray diffraction (XRD) measurements at 25–55 GPa and 2,320–3,260 K in a laser‐heated diamond‐anvil cell. We employed a recently developed analytical method that enables density derivation from diffuse scattering signals in XRD data observed in a limited range of diffraction angles. The EoS of liquid FeS obtained in the present experiments exhibits higher compressibility and smaller thermal expansivity under Martian core conditions than the extrapolations of earlier experimental results. We calculated the density of liquid Fe‐S with a composition between Fe and FeS from those of these end‐member liquids considering non‐ideal mixing. When sulfur is a single light element, the observed mean core density requires 17–24 wt% S and 23–34 wt% S for two distinct thermal structures, hot‐ and cold‐core models, respectively.

DOI： 10.1029/2025je009596

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Other Link： https://agupubs.onlinelibrary.wiley.com/doi/full-xml/10.1029/2025JE009596

Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.epsl.2025.119785

Web of Science

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.epsl.2023.118449

Web of Science

Scopus

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：European Association of Geochemistry  

DOI： 10.7185/geochemlet.2218

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It has been assumed that hydrogen is negligibly incorporated into core-forming metals below $\sim$3 GPa, and therefore the presence of hydrogen in iron cores of small terrestrial bodies including the moon has not been considered. Here we performed high-pressure melting experiments on the Fe-H system under H$_2$-saturated conditions, combined with synchrotron X-ray diffraction (XRD) measurements. Results demonstrate substantial depression of the Fe-H melting curve compared to that for Fe at 1.0-3.3 GPa, indicating that hydrogen is incorporated into liquid iron even at low pressures less than 1 GPa and the solubility is enhanced with increasing pressure. Based on the density of liquid Fe-H derived from diffuse scattering signal in XRD data, we found that the solubility of hydrogen in liquid iron is about 0.9 wt% at 3.6 GPa and likely enhanced to 1.2 wt% at 5 GPa corresponding to lunar core conditions. The 1.2 wt% H causes 9 % density reduction, which might fully explain the observed density deficit of the lunar core with respect to iron, depending on the density estimate from seismological data.

arXiv

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Other Link： https://arxiv.org/pdf/2604.12222v1

Language：Japanese   Publishing type：Research paper, summary (national, other academic conference)  

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Authorship：Lead author   Language：Japanese   Publishing type：Research paper, summary (national, other academic conference)  

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Authorship：Lead author   Language：English   Publishing type：Article, review, commentary, editorial, etc. (international conference proceedings)  

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Language：English   Publishing type：Article, review, commentary, editorial, etc. (international conference proceedings)  

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Event date： 2026.5

Language：English   Presentation type：Oral presentation (general)  

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Event date： 2026.3

Language：Japanese   Presentation type：Symposium, workshop panel (public)  

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Event date： 2025.10

Language：English   Presentation type：Symposium, workshop panel (nominated)  

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Event date： 2025.9 - 2025.10

Language：English   Presentation type：Poster presentation  

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Event date： 2025.9 - 2025.10

Language：English   Presentation type：Poster presentation  

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Award type：Award from international society, conference, symposium, etc.  Country：Japan

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