These agglomerates (~3 to 15 mm) were turned into fine and medium sand grains (0.1 to 0.3 mm) using the laser-induced breakdown spectrometer (LIBS fig. These structures arise from the cementation of fine and medium sand grains. S1, B and E) and agglomerated particles (granules/aggregation) on the dark dunes ( Fig. 2B and fig. Pictures taken by the MSCam and the microscopic camera show that different forms of cementation exist on dune surfaces, with a crust developed on the bright dunes ( Fig. 2B and fig.

In particular, surface morphological features of sand dunes at low latitudes are rarely investigated, which hampers our understanding of hydroclimatic variations in the region where the comparatively mild ground temperatures may support life. In this case, studies on small-scale (i.e., <1 m) surface features on a diversity of landscapes are therefore essential to depict a complete picture of contemporary hydrological processes on Mars. If this projection is right, then there may be small amounts of surface water hidden from view. Numerical modeling ( 16) suggests that suitable climatic conditions for liquid water can occur on present-day Mars. The main argument against the wet hypothesis lies in the inadequate amount of water required to trigger such large-scale (i.e., at least several hundred meters long) slope flows ( 14). For example, some conflicting scenarios such as dry versus wet mechanisms have been proposed for their formation ( 14, 15). In contrast, indirect evidence for modern hydrological activity above ground including recurring slope lineae ( 12) and gullies ( 13) remains under debate. Nevertheless, the observed liquid drops on the robotic arms of the Phoenix rover indicate that conditions allowing for the existence of liquid saline water emerge at high-latitude regions of Mars in summer because the thermodynamics of freeze-thaw cycles can lead to the formation of saline solutions with freezing temperatures lower than current summer ground temperatures ( 11).

On the Edge by C.D. Reiss