The Determination of Mercury's Libration with BepiColombo MORE Investigation using Optical Navigation

The ESA mission BepiColombo will reach Mercury in late 2025 to begin an extensive exploration of the planet. The Mercury Orbiter Radio-Science Experiment (MORE) is one of the 11 scientific instruments on board the Mercury Planetary Orbiter (MPO), which will enter a polar and eccentric orbit around the planet. The main aim of the MORE investigation is to study the gravitational field of the planet to obtain scientific findings in geophysics, geodesy, and improve current knowledge about Mercury’s internal composition and dynamics.

Specifically, one of the objectives of MORE is to increase confidence on the state and size of Mercury’s core, which is expected to be at least partially molten and decoupled from the mantle. Such study can be performed by estimating the second-degree coefficients of the gravity field, Mercury’s 88-day libration amplitude, and the planet’s obliquity. The comprehensive estimation of these parameters requires synergy between classic radiometric tracking and optical navigation algorithms to obtain accurate joint information about the state of the orbiter and estimate the amplitude of the forced longitudinal libration of Mercury from differences in the position of surface features as MPO passes over the same region at different epochs.

In this work, we present the results of our simulations of the MORE radio science experiment for the estimation of the libration amplitude of Mercury during the science phase of BepiColombo, using optical observables extracted from simulated images of Mercury.