Flow processes associated to liquid water on Mars
Active flow processes are currently ongoing at the surface of Mars and have been revealed trough monitoring campaigns using high-resolution images of landforms such as gullies (Fig. 1) or RSL (Recuring Slope Lineae).
The physical processes involved in their formation and their current activity have not been unambiguously identified and are still under debate. One possible candidate is liquid water, but under current martian conditions liquid water is transient and can only be present in limited amounts. However the surface temperature can locally exceed the melting point on present-day Mars, leading to rapid boiling of liquid water. So far, little attention has been paid to the role of boiling in sediment transport processes although it can potentially be of primary importance for the understanding and interpretation of water-driven processes and present-day surface activity on Mars. Recent study has highlighted that boiling water can drive unusual transport mechanisms leading to an enhanced transportation volume. We conduct a series of experiments under low pressure to investigate the transport capacity of sediment by liquid water under Martian-like surface conditions. We tested the influence of two parameters, the water and sediment temperature (Fig. 2).
We find that sediment transport by boiling is characterized by grain ejection, granular avalanches and a singular process of levitating pellets, which according to our scaling calculations are more effective transport processes under Martian gravity. Among the two parameters tested, the sand temperature is the main driving parameter for transport via boiling while water temperature plays a minor role. We highlight that if liquid water is present at the surface of Mars boiling could play an important role in understanding the recent changes in Martian gullies or RSL. It should not be neglected when analysing and modelling water flow features on Mars. These experimental results can help to interpret orbital images such as the ones from HiRISE and CaSSIS.