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Geologic context of recurring slope lineae in Melas and Coprates Chasmata, Mars



One of the major Mars discoveries of recent years is the existence of recurring slope lineae (RSL), which suggests that liquid water occurs on or near the surface of Mars today. These dark and narrow features emerge from steep, rocky exposures and incrementally grow, fade, and reform on a seasonal basis and are detected in images from the High Resolution Imaging Science Experiment camera. RSL are known to occur at scattered midlatitude and equatorial sites with little spatial connection to one another. One major exception is the steep, low-albedo slopes of Melas and Coprates Chasmata, in Valles Marineris where RSL are detected among diverse geologic surfaces (e.g., bedrock and talus) and landforms (e.g., inselbergs and landslides). New images show topographic changes including sediment deposition on active RSL slopes. Midwall locations in Coprates and Melas appear to have more areally extensively abundant RSL and related fans as compared with other RSL sites found on Mars. Water budget estimates for regional RSL are on the order of 105 to 106 m3 of fluid, for depths of 10 to 100 mm, and suggest that a significant amount of near-surface water might be present. Many RSL are concentrated near local topographic highs, such as ridge crests or peaks, which is challenging to explain via groundwater or ice without a recharge mechanism. Collectively, results provide additional support for the notion that significant amounts of near-surface water can be found on Mars today and suggest that a widespread mechanism, possibly related to the atmosphere, is recharging RSL sources.