Mercury interior characteristics inferred from geodetic measurements

Mercury exhibits unique dynamics because of its proximity to the Sun and its elliptical orbit. The eccentricity combined with the Sun's gravitational pull, results in periodic variations in tidal forces and associated surface deformations. In particular, the tidal forces generate periodic variations in the shape and gravity of Mercury, depending on its internal composition and structure. These variations, described as "Tidal Love numbers" (TLNs), are valuable indicators of Mercury’s deep structure. Precise measurements such as by laser and radar altimetry are required to estimate these deformations as well as radio science for precise determination of changes in the gravity field. Recent research by Bertone et al. (2021) used data from the Mercury Laser Altimeter of the MESSENGER spacecraft to estimate the h2 tidal Love number. Previous studies, such as those by Steinbrügge et al. (2018) and Goossens et al. (2022), offer additional insights into relationships between Mercury deformation and interior. However, there are still significant uncertainties in geodetic measurements that prevent unique models of Mercury's deep interior.

To better understand the internal structure of Mercury, we plan to use new reduction techniques for MESSENGER altimetry (Xiao et al., this meeting) and recently obtained physical constraints on the interior of the planet. Our approach will involve exploring various combinations of radii, densities, shear modulus, and viscosities while considering the rheology of each layer from the planet's core to its surface. We will then compare our modelled results with available estimates of tidal deformation, mass, and moment of inertia, to decipher the interior composition of Mercury.

References:

Steinbrügge, G., Padovan, S., Hussmann, H., Steinke, T., Stark, A., & Oberst, J. (2018). Viscoelastic tides of Mercury and the determination of its inner core size. Journal of Geophysical Research: Planets, 123(10), 2760-2772.

Bertone, S., Mazarico, E., Barker, M. K., Goossens, S., Sabaka, T. J., Neumann, G. A., & Smith, D. E. (2021). Deriving Mercury geodetic parameters with altimetric crossovers from the Mercury Laser Altimeter (MLA). Journal of Geophysical Research: Planets, 126(4), e2020JE006683.

Goossens, S., Renaud, J. P., Henning, W. G., Mazarico, E., Bertone, S., & Genova, A. (2022). Evaluation of recent measurements of Mercury’s moments of inertia and tides using a comprehensive Markov chain Monte Carlo method. The Planetary Science Journal, 3(2), 37.

Xiao, H., Stark, A., Steinbrügge, G., Briaud, A., Lara, L M., Gutiérrez, P J., [IN PREP]. Mercury’s tidal Love number h2 from co-registration of reprocessed MLA profiles