The interior of Mercury and what we can learn about it from the upcoming missions

Present estimates of the Hermean core mass and volume depend mostly on our confidence in cosmochemically constrained values of the average silicate shell and core densities The Messenger and BepiColombo missions will measure very accurately the gravity field, the topography and the rotation parameters of the planet. In addition, BepiColombo will attempt to measure the tidal Love numbers. The moment of inertia C about the rotation axis will be determined from the degree 2 components of the gravity field and from measurements of the obliquity and the libration frequency of the rotation axis (Peale 1988). The ratio C_m/C between the moment of inertia of the solid planet to the moment of inertia of the entire planet, both about the rotation axis, will additionally be obtained. If the core is liquid or if there is a liquid outer core, C_m/C will be around 0.5. In this case, C_m can be identified with the moment of inertia of the silicate shell. If the core is solid, C_m/C will be about 1. The moment of inertia C can be used to test and refine present models although the non-uniqueness of present models cannot be removed entirely, in particular in the likely case that there is a substantial inner core. C and C_m/C can be used to calculate the inner core radius and the outer core density while assuming the silicate shell density and the inner core density. The inner core radius can be estimated if the inner core radius is greater than 0.5 core radii. These values can be checked against the Love numbers of the planet. However, the Love numbers will again show significant effects of an inner core only if the inner core radius is larger than 0.5 core radii. The higher order components of the gravity field can be used to estimate core-mantle boundary undulations and crust thickness variations. The former will dominate the gravity field at long wavelength, while the latter will dominate at short wavelengths. Peale, S.J., 1988. Rotational dynamics of Mercury and the state of its core. In: F. Vilas, C.R. Chapman, M.S. Matthews (Eds.) Mercury. The University of Arizona Press, Tucson, Arizona and London.