Briaud, Arthur ; Xiao, Haifeng ; Rivoldini , Attilio ; Tosi, Nicola ; Hussmann, Hauke ; Stark, Alexander ; Oberst, Jürgen

Poster presented at Mercury 2026 – An International Meeting on Planet Mercury, Leuven, Belgium on 2026-09-01

Abstract: Mercury’s tidal Love numbers provide key constraints on the planet’s internal structure and mantle rheology (Padovan et al., 2014; Steinbrügge et al.,2018). However, the relative contributions of elastic deformation, anelastic relaxation, and viscous dissipation remain difficult to disentangle from their real parts alone. Here, we develop a computational framework to investigate Mercury’s complex degree–two tidal response, including h2, k2, and l2, over a wide range of forcing periods and rheological assumptions. We generate large ensembles of discretised-layer interior models using Markov Chain Monte Carlo sampling. The models include a solid inner core, a liquid outer core, a viscoelastic mantle, and a crust, and are constrained by Mercury’s mass, normalized polar moment of inertia, solid outer shell moment of inertia, and observed h2 and k2 e.g, (Margot et al., 2012; Konopliv et al., 2020; Xiao et al., 2025). For each interior model, we compute complex Love numbers for four rheological prescriptions: Hooke, Maxwell, Andrade, and Sundberg– Cooper. We then use Random Forest regression, permutation importance, and cross-validation to identify the parameters that most strongly control the tidal response. Our results show that real parts of h2 and k2 are controlled primarily by large-scale structure and elastic properties, whereas the imaginary parts of h2 and k2 are frequency dependent and provide direct diagnostics of mantle dissipation. Maxwell models concentrate dissipation around a characteristic relaxation timescale, while Andrade and Sundberg–Cooper rheologies produce broader dissipation spectra. These results demonstrate that elastic Love numbers alone cannot discriminate between plausible mantle rheologies. The complex tidal response provides predictive metrics for interpreting forthcoming BepiColombo measurements and refining constraints on Mercury’s interior, rheology, and thermal evolution.

Funding: 3PRODPLANINT/3PRODPLANINT/3PRODPLANINT