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

Mercury’s unique interior structure and magnetic field generation remain to be fully un23 derstood. We construct models to further constrain Mercury’s interior and test the hy24 pothesis 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 constraints. A high normalized moment of inertia (MoI) of MoI = 0.346±0.014, in combination with thermal and geochemical constraints, favors models with an Earthlike mantle density of ∼ 3300 kg/m3 , an inner core ≤ 1050 km in radius, and a core silicon content of at least 6 wt%. In contrast, a lower value of MoI = 0.333±0.005 favors models with lower mantle densities of ∼ 3100 kg/m3 , an inner core radius in the range of 850–1450 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 ∼ 4 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.