Work

Interior Models of Mercury and Conditions for Iron Snow Formation in a Fe‐S‐Si Core

Year: 2026

Type: article

Abstract: Mercury's unique interior structure and magnetic field generation remain to be fully understood. We construct models to further constrain Mercury's interior and test the hypothesis that iron snow within the liquid core drives the dynamo. We build upon previous models by incorporating an updated iron‐sulfur‐silicon (Fe‐S‐Si) core alloy composition and use a Monte Carlo approach to explore the parameter space consistent with geodetic and geophysical constraints. A high normalized moment of inertia (MoI) of , in combination with thermal and geochemical constraints, favors models with an Earth‐like mantle density of kg/, an inner core km in radius, and a core silicon content of at least 6 wt%. In contrast, a lower value of MoI favors models with lower mantle densities of kg/, an inner core radius in the range of 850–1,450 km, and a core silicon content less than 8 wt%. We also show that the formation of iron snow requires a sulfur concentration greater than wt%. However, the expected geochemistry of the core restricts the sulfur content to less than 2 wt%. This inconsistency suggests the absence of snow layers in Mercury's present‐day core and that its dynamo is not driven by sulfur‐induced iron crystallization.

Source: Journal of Geophysical Research Planets

DOI: 10.1029/2025je009368