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 model compositions provide 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, an analog composition of the Mercurian core, using a multi-anvil apparatus. 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 lowers 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.