Liquidus determination of the Fe-S and (Fe, Ni)-S systems at 14 and 24 GPa: Implications for the Mercurian core

Abstract

Mercury has fascinated researchers for decades due to its sizable metallic core and weak magnetic field. The behavior of Fe-S and (Fe, Ni)-S systems provides constraints on core conditions and regimes of solidification to predict magnetic field strength. In this study, we investigate the melting behavior of the (Fe, Ni)-S system, a candidate composition to model the Mercurian core. We observe that the Fe-S liquidus has an inflection point at ∼10 wt.% S at 14 GPa and ∼11.5 wt.% S at 24 GPa, while (Fe, Ni)-S does not. At 24 GPa, Ni may lower the melting point of the Fe-S system by as much as 300°C, indicating that solidification models and adiabatic calculations must account for the presence of Ni.