Constraints on Mercury's Interior from Tidal Love Numbers Models

Abstract

Mercury's unique orbital and rotational dynamics, shaped by its proximity to the Sun and its elliptical orbit, result in periodic variations in tidal forces. These forces induce changes in the planet's shape and gravitational field, which are described by Tidal Love Numbers (TLNs). TLNs are essential for constraining the internal structure of Mercury, including core size, mantle composition, and crustal properties [1, 2, 3, 4, 5]. Accurate estimates of these deformations require precise measurements, such as laser and radar altimetry for surface deformation and radio science to detect variations in the gravity field, e.g. [6]. In addition, other instruments can also be used to detect radial tidal deformation. For example, the Advanced Pointing Imaging Camera (APIC), Lunar Laser Ranging (LLR), and Earth-based repeat-pass Synthetic Aperture Radar (SAR) interferometry provide valuable capabilities for measuring such deformations [7, 8, 9]. Moreover, different flattening of Mercury's internal layers may also affect its tidal response. For example, inner core libration may play an important role in shaping these deformations e.g., [10]. Mercury's TLNs are then particularly sensitive to lateral heterogeneities, that can result from spatial variations in thermal state, composition, and physical properties. These lateral variations introduce significant complexity into the tidal response of the planet and influence the elastic and viscous behavior of its layers. To study these effects, we will use advanced numerical models that incorporate geophysical and thermodynamic constraints. Our models will simulate the effects of lateral heterogeneities, including variations in mantle composition, temperature distribution, and rheological properties in the crust, mantle, and core. For example, on icy moons, regions with elevated temperatures or different mineralogical compositions exhibit different mechanical responses, contributing to spatially heterogeneous tidal deformation [11, 12].