Physical models and predictions for recurring slope lineae formed by wet and dry processes

The observation of low albedo, elongated and transient features lengthening downhill on Mars has attracted wide interest because of the possible role of aqueous fluids in their formation. These recurring gravity-driven processes, called Recurring Slope Lineae (RSL), remain mysterious in that, although the influence of local climate conditions has been established, their nature (dry versus wet) and the mechanisms that govern their growth and fading are debated. We present three different physical models for the growth of RSL, the first two are wet-based models with different aqueous fluid evaporation models and the last is based on dry granular theory. We discuss the prediction of each model with regards to the growth and fading of RSL and their morphology. We finally discuss the strengths and weaknesses of these models in light of what we currently observe on Mars. We find that both wet and dry RSL scenario face challenges, mostly regarding aspects of mass balance. However, water-based scenarios provide a consistent framework to reconcile the different sets of morphological observations made on RSL.