Dunnigan, Abigail H. ; Liu, Dunyu ; Steinbrügge, Gregor B. ; Rivoldini, Attilio ; Dumberry, Mathieu ; Cao, Hao ; Soderlund, Krista M.

published in Journal of Geophysical Research: Planets, 131 issue 4 (2026)

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 0.346 ±0.014, in combination with thermal and geochemical constraints, favors models with an Earth-like 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 ±0.005favors models with lower mantle densities of ∼3100 kg/m3, 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 ∼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.

DOI: 10.1029/2025JE009368
Funding: 3PRODPLANINT/3PRODPLANINT/3PRODPLANINT