Mercury's Tidal Love Number h 2 ${h}_{2}$ From Co-Registration of MLA Profiles

Abstract

Due to its eccentric orbit, Mercury experiences a varying gravitational pull from the Sun along its orbit, leading to periodic surface tidal deformation. The previous measurement of Mercury's tidal $h_2$ by Bertone et al. (2021, https://doi.org/10.1029/2020je006683) is based on minimizing height differences at cross-overs of the Mercury Laser Altimeter (MLA) profiles. However, this method can suffer from significant interpolation errors. In this study, we apply an alternative approach, which is based on the co-registration of reprocessed MLA profiles. For the reprocessing, we account for the pointing aberration and incorporate an updated spacecraft orbit model. Within the study region of 77°N to 84°N, we obtain a tidal $h_2$ of 0.92$\pm$0.58 (3-$\sigma$). This value is compatible with current interior structure and rheology models, but significantly lower than the previous estimate of 1.55$\pm$0.65 (3-$\sigma$). When combined with recent tidal $k_2$ estimates, our measurement favors a small to medium-sized inner core.