Experimental study of sediment transport processes by liquid water and brine under Martian pressure

We present here an experimental study to compare the behaviour of water and brine releases over loose sediments under present-day Martian pressure. Water has been invoked to explain current or past Martian surface features for decades. Recent studies have indicated that current surface conditions are, in certain times and places, compatible with the transient existence of liquid water or brine. However, the behaviour of water or brine releases over loose sediments under low Martian atmospheric pressure has been poorly studied. We performed 33 experiments of water and brine (MgSO4 at 19 wt%) releases over sandy slopes of various temperatures (0 °C to 20 °C), in a chamber allowing the reproduction of Martian pressure 6–7 millibars (mbar). We observe sediment transport mechanisms, that do not occur on Earth, caused by the boiling of water or brine at Martian pressures: grain ejection and “levitation” of sand pellets on cushions of vapour. The main parameter controlling the behaviour of the flow is the temperature of the substrate. Water and brine flows transport similar volumes of sediment under Martian pressure. We show that the grain ejection is the most efficient transport mechanism, dominating the volumes of sediment transported. Pellet “levitation” should lead to longer features formed with brine than with pure water on Mars. Boiling induced sediment transport requires much less water than sediment transport by overland flow to form morphologies similar in size or volume. Moreover, our one-dimensional climate model runs reveal that the temperatures at which we observe those types of transport are predicted to occur at the Martian surface today and in the past. When scaled to Mars, the morphologies we observe with water and brine experiments should be resolvable using the High-Resolution Science Experiment (HiRISE) camera at ∼25 cm/pix. Overall, our results show that boiling must be taken into account when considering sediment-rich flows under recent or current Martian conditions.