Exploring Mercury's Tidal Stresses Through Time: Effects of Orbital Eccentricity, Rotational Dynamics, and Their Implications for Tectonics

Mercury's tectonics are assumed to have originated mainly from the planet's cooling and contraction processes, but tidal stresses are hypothesized to have influenced the orientations of scarp features and faults, potentially imparting a preferred orientation during their formation. Global cooling typically leads to isotropic contraction with minimal shear deformation. However, some shear kinematics have been identified in the form of oblique-slip deformation along lobate scarps and high-relief ridges through mapping fault patterns and structural morphologies. In this study, we explore the present and possible past tidal stress values through potential evolutions for the spin and eccentricity of Mercury, in particular the suggested spin/orbit configurations of 5/2, 2/1, and 3/2 before final capture and their progressions through the past 2 billion years. Our findings indicate that Mercury currently experiences tidal stresses of up to ∼±15 kPa, while in the past, increased eccentricity and spin rates could have elevated these stresses to ∼±40 kPa. Although shear failure was not observed in the modeled scenarios, we analyzed the effects of lowering the crust's shear strength to identify the preferred shear direction. Our results show that tidal stresses influenced by Mercury's orbital eccentricity and spin rate may have played a role in determining the shear direction of inferred strike-slip kinematics on a spinning Mercury. The observed alignment between the timing of shear failure during orbit and the increase in compressional normal stress suggests a possible correlation to the structural interpretation that Mercury's shear deformation is transpressional in nature.