Determining the amplitude of Mercury's long period librations with the BepiColombo radio science experiment

The Mercury Orbiter Radio science Experiment (MORE) is one of the experiments on-board the ESA/JAXA BepiColombo mission to Mercury. A crucial goal of MORE is to determine the gravity field and rotational state of Mercury in order to enable a better understanding of the planet's geophysics. The authors have recently reported on the results of a set of simulations of the MORE gravimetry and rotation experiments, carried out with the dedicated ORBIT14 software. Since that time, the launch date has been postponed twice, leading to a shift of more than one year in the orbital phase of the mission. Actually, the updated schedule results in a more suitable planetary configuration to determine the amplitude of the forced librations in longitude induced by Jupiter. In fact, the amplitude can be considerably enhanced due to a near-resonance with the free librations period, a key parameter to constrain the interior structure of Mercury. We show that the newest launch date allows the measurement of the long period librations amplitude forced by Jupiter with an accuracy of some tenth of arcseconds, a significant improvement with respect to the results with the previous mission schedule.