Can Mercury’s heterogeneous tectonic record be explained by geodynamic models?

Kurzfassung

Mercury’s geodynamic history has been characterized by global contraction due to planetary cooling and inner core growth. The planet likely experienced the largest radius change out of all Solar System bodies, with most occurring early in its thermal evolution (Watters, 2021, Peterson et al., 2021, Grott et al., 2011, Byrne et al., 2014). Such contraction has been recorded in tectonic landforms on the surface, which can be used to reconstruct radius changes from tectonic strain. However, estimates substantially vary between < 2 km (Watters, 2021) and up to 7 km (Byrne et al., 2014), depending on whether wrinkle ridges are taken into account as contributing to global contraction. A recent study by Broquet & Andrews-Hanna (2026) revisited Mercury’s tectonic record and found global contraction values of 8.3 ± 4.5 km, with a conservative range of 6.3 ± 3.2 km when considering only primary tectonic landforms. Contraction was found to substantially vary spatially, with some regions displaying a near‐zero record of contraction. The authors also propose high contraction rates of 0.02 – 0.04 km/Myr from 4.1 – 3.9 Ga, followed by significantly lower contraction rates during the later evolution. Additionally, an upcoming study by Nishiyama et al. (submitted) suggests that surface roughness can obscure tectonic features on the surface, leading to an underestimation of Mercury’s global contraction by up to 30 %.