Plume effects on Martian surface: Revealing evolution characteristics of plume-surface interaction at Tianwen-1 landing site

Engine plumes can seriously erode the Martian surface during the landing phase, causing a substantial alteration of the terrain of the immediate touchdown area and beyond. Furthermore, large amounts of lifted dust can block the view of boulders or craters, posing a serious threat to the lander's safety. Improving our understanding of the plume-surface interaction can reduce the risk of failure on a Mars landing mission. In situ studies on this subject are limited, particularly those relating to high-thrust single-nozzle engines. The Tianwen-1 represents the only Mars landing mission that employed such an engine with a thrust of ∼3000 N during the landing phase: Its success represents a unique opportunity in addressing this issue, providing an important reference for future Mars return missions. Here, we report the evolution characteristics of the plume-induced regolith erosion and the plume impingement effect measurements at the Tianwen-1 landing site. The results show that depressions and infilling are a complex process accompanying the changing of patterns as the lander descends. Specifically, the plume will seriously erode the area beneath the nozzle, causing the formation of a deep crater. Meanwhile, the expanding radial flow tends to flatten the peripheral area of the lander, which depends on the homogeneity of the regolith. To better quantify the impingement effects, some crucial parameters were extracted. The measured volume, diameter, and depth of the crater are 0.115 ± 0.019 m³, 1.50 m, and ∼0.35 m, respectively. We also calculated the total erosion area and volume as 4879.4 ± 297.7 m² and 376.9 ± 102.2 m³. In addition, plume-induced infilling/erosion depths and rates during the landing phase were measured. Further, we investigated the shallow stratigraphic architecture exposed by the plume-induced crater beneath the lander, showing that it represents probably dust/sand-coated black rocks above at least ~35 cm thick, bright reddish materials. These results provide valuable insights into the plume impingement effects on the Martian surface and the shallow subsurface layer at the Tianwen-1 landing site, which will benefit future Mars explorations.