Mercury’s Internal Structure

Abstract

We describe the current state of knowledge about Mercury's interior structure. We review the available observational constraints, including mass, size, density, gravity field, spin state, composition, and tidal response. These data enable the construction of models that represent the distribution of mass inside Mercury. In particular, we infer radial profiles of the pressure, density, and gravity in the core, mantle, and crust. We also examine Mercury's rotational dynamics and the influence of an inner core on the spin state and the determination of the moment of inertia. Finally, we discuss the wide-ranging implications of Mercury's internal structure on its thermal evolution, surface geology, capture in a unique spin-orbit resonance, and magnetic field generation.

Terrestrial planet compositions controlled by accretion disk magnetic field

“…The resulting mass model for Mercury has 26 ± 5% silicate shell and 74 ± 5% core. This estimate compares favorably with that presented by Margot et al (2018) for his Preliminary Reference Mercury Model (PRMM; 74% core and 26% silicate sphere).…”

“…Here we use our earlier compositional models for the Earth (McDonough 2014) and Mars (Yoshizaki and McDonough 2020) and model the recent data from the MESSENGER mission to Mercury (Margot et al 2018;Nittler et al 2018) to predict its bulk composition (Table 1), which is verified to be consistent (Alexander 2019a;2019b;McCall 1968;Ivanova et al 2008;Gosselin and Laul 1990;Wasson and Kallemeyn 1990;Bischoff et al 1993 (Lewis 1972;Lodders and Fegley Jr. 1998;Stacey 2005).…”

“…The bulk composition (i.e., abundant elements O, Fe, Mg, Si, Ni, Al, Ca, and S) of Mercury was defined to be consistent with its geodetic observables: mass, density, and MOI (moment of inertia) (Margot et al 2018), compositional trends for Earth and Mars, and chondritic ratios showing limited variation (≤ ± 10%). We used the density of Mercury and assumed a thermal gradient in the protoplanetary disk outward from the accreting Sun to constrain the model.…”

Deriving Mercury Geodetic Parameters With Altimetric Crossovers From the Mercury Laser Altimeter (MLA)

“…Because the estimate of Genova et al (2019) was based on gravity, indicating a sensitivity to the whole planet, and ours on measurements related to the crust, this further illustrates a possible difference between these measurements. While it is unclear which measurement type (if any) would yield the correct answer on its own, one has to be aware of these differences, because they have consequences for the resolved interior models: a higher polar moment as resolved from crustal measurements results in a larger outer core radius, and might not be able to constrain a solid inner core (Hauck et al, 2013;Margot et al, 2018). We note the latter in our results as well.…”

The Influence of a Fluid Core and a Solid Inner Core on the Cassini State of Mercury

“…It is on the basis of the observed mantle obliquity that the polar moment of inertia of Mercury is inferred (e.g., Margot et al, 2018;Peale, 1976). Inherent in this calculation is the built-in assumption that the mantle obliquity does not deviate from that of a rigid planet by a substantial amount.…”