Presentation Date: Feb 14, 2026
AGSA Abstract
Constraining the temperature at Earth’s inner core boundary (ICB) is critical for modeling the planet’s thermal evolution, inner core formation, and geodynamo. While geophysical constraints have narrowed down the depth of the ICB, considerable uncertainty remains regarding the temperature at which iron alloys solidify under core pressures. This temperature directly affects interpretations of heat flow, core composition, and Earth’s deep interior dynamics. Although the melting behavior of pure iron has been widely investigated, fewer studies have systematically examined how light elements (H, C, O, S, Si, Ni) change this behavior under ICB-like pressures (~330 GPa). Here, I use molecular dynamics simulations based on a machine-learning interatomic potential trained on first-principles data to explore binary Fe-light element alloys across a range of atomic concentrations. Melting points are obtained with the solid–liquid coexistence method, identifying the temperature window where solid and liquid phases coexist in equilibrium. The simulations show that H, C, O, S, and low levels of Si systematically depress iron’s melting point, with reductions of ~800 K (H), 1000 K (C), 900 K (O), 450 K (S), and 150 K (Si) at 8 at% compared with pure Fe (6230 K). By contrast, higher Si contents (>1 at%) and all tested Ni concentrations raise the melting temperature, with Fe–Ni alloys reaching 6430 K at 2 at%. These contrasting trends highlight the strong element-specific control of light elements on the thermal stability of core alloys. Overall, the modeled melting depressions from H, C, O, and S indicate that inner core solidification may start at lower temperatures than suggested by pure iron alone. These results help refine estimates of ICB temperature and provide composition-dependent constraints for models of core structure, evolution, and the geodynamo.
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