Amazonian-aged glacial melting recorded by a subglacial paleolake and regionally widespread eskers on Mars

The mid-to-late Amazonian period on Mars (ca. 0−1 Ga) was cold and hyperarid, with an extremely limited role of liquid water. Abundant midlatitude viscous flow features (VFFs; putative debris-covered glaciers) that formed during this time are thought to be the partially retreated remnants of larger, thicker, predominantly cold-based ice masses deposited by snowfall. Small numbers of eskers (ridges of glaciofluvial sediment deposited in ice-confined meltwater tunnels) associated with VFFs have been attributed to rare, spatially restricted past subglacial melting driven by localized geothermal heating. Here, we present two key findings based on analysis of orbital images and elevation data. First, VFF-associated eskers distributed throughout a 650-km-long plateau system in the Tempe Terra region necessitate more widespread occurrences of Amazonian subglacial melting and more spatially extensive heating (e.g., a geothermal hotspot and/or regional climate change) than previously understood. Second, two of the eskers are associated with a landform assemblage consistent with meltwater drainage into a subglacial paleolake. This suggests that VFFs were capable of supporting subglacial lakes when they were thicker and more extensive. Glaciers in Mars’ midlatitudes are key targets for robotic missions aiming to search for life, reconstruct environmental change, and characterize in situ water resources for human missions. On Earth, subglacial lakes support microbial ecosystems under extreme conditions, and paleolake deposits have high potential for preserving biosignatures in the geologic record. Hence, subglacial paleolake deposits proximal to Mars’ midlatitude glaciers represent high-priority targets for future exploration.