Laboratory model of Martian gullies

Liquid water is currently not stable on the surface of Mars. Therefore, we should be careful if we assume the hypothesis of the formation of young geological formations on Mars, if it requires the presence of liquid water. Note also that p-T conditions on the surface of Mars are not suitable for liquid CO2. Therefore, the geological young structures on the surface of Mars are not probably the result of processes requiring the liquid. Here we present the results of our laboratory experiments on the processes that may be responsible for the formation of gullies on the surface of Mars.Gullies are usually found on steep slopes. A gully forms usually a single incised channel. There is a dendritic alcove at the upper end. A fan-shaped deposited material ('apron') is at the lower end. Gullies are estimated to be relatively young. Some of gullies could be recurrent seasonal structures. Terrestrial gullies are often the result of stream of liquid water. Initially, such an origin was also attributed to Martian gullies.  This would imply that in the recent (geological) past there were water streams on the surface of Mars capable of carving out a significant channel (a 'river bed'). An alternative hypothesis assumes that the gullies are the result of the movement of debris. However, many gullies are on slopes with a low inclination, too low for flows of  debris. Moreover, the sinuous shape of some gullies suggests flow of liquid. We performed experiments on a scale 0.5-2 m using dust, sand, gravel, pebbles and other granular matter (as the model of regolith). With the appropriate geometry of the model, it was possible to obtain the basic qualitative features of gullies, including the channel and the apron (in the lower end). Adequate quantitative scaling remains a problem (e.g. channel sizes depending on the properties of the material used, model dimensions and geometry, etc.). Of course, ourresults do not meanthat gullies cannot be the result of temporalbrinesoccurring on Mars, but theyindicate the possibility that some gullies could have formed without liquid water. We will continue our research to improve our models of gullies.