First Global Map of Mercury’s Surface Roughness Down to Kilometric Baselines: Implications for the Planet’s Geologic Evolution

Abstract Surface roughness on Mercury is a crucial observable for characterizing Mercury’s geologic processes such as volcanism, impact cratering, and volatile sublimation. However, roughness mapping at kilometer-scale baselines has previously only been successful for the north polar region, due to the limited coverage of MESSENGER’s Mercury Laser Altimeter (MLA) and low spatial resolution of the existing global digital terrain models (DTMs). This study presents the first global map of surface roughness on Mercury down to 5 km baselines, combining the MLA data with a new global image-based DTM that offers a spatial resolution of 2–5 km. The created map reveals correlations between surface roughness and Mercury’s geologic features, such as smooth plains, young craters, and chaotic terrain at the Caloris antipode. Roughness distribution shows a positive correlation with the crater density, indicating its potential use as a proxy for surface age. Furthermore, correlation between surface roughness and crustal thickness indicates that crustal thickness influences extrusive volcanism because surface roughness reflects geologically recent volcanic resurfacing on Mercury. This correlation suggests that Mercury’s crust may act as a buoyancy barrier to extrusive volcanism, as has been suggested for the Moon. This first global roughness map provides a foundation for comparing the geologic evolution of terrestrial planets from a topographic perspective.