A Chronology of Mars Hydrological Evolution from Impact Degradation

Introduction: Impact crater degradation provides a powerful tool to analyze past Martian hydrological evolution. Previous studies concluded that large impact craters were strongly degraded during early Martian history, whereas younger craters are only weakly degraded [1]. Degraded craters are therefore one of the main lines of evidence for a warmer climate on early Mars. Global altimetry and recent high resolution imagery enable us to revisit this work. In particular it allowed us to identify preserved impact ejecta, which is strong evidence for limited degradation, and fluvial landforms on rims. These details were particularly pertinent in the case of the craters with alluvial fans [2]. We chose to focus our study on the craters with alluvial fans; their degradation stage, the type of fluvial erosion, and on their chronology relative to other climatic markers such as the global valley networks.