The tests collected by robotic explorers sent to Mars suggest that the red planet was millions of years ago a humid world, bathed in oceans and rivers in which even gigantic tsunamis were produced. More recently, there have been indications that water is still flowing at least seasonally. Images taken by the Mars Reconnaissance Orbiter (MRO) probe suggested that, beneath the planet's surface, certain amounts of salt water remain liquid and drain to the surface from time to time. In those photographs appeared dark spots that could be explained with the presence of liquid water at about 23 degrees below zero, something possible thanks to the salts that would contain. These flows would also make the possibility of life in the Martian subsoil more likely. This week, however, a new study, published in the journal Nature Geoscience, offers an alternative explanation for the spots captured by MRO. The work, carried out by the U.S. geological Survey, raises that instead of water the stains are "granular flows" or, in common language, sand streams moving in a similar way to liquid water. This new scenario would alienate the possibility of finding life on the present Mars. The stains, baptized by scientists as recurrent lines of descent (RSL), have been found all over the planet, from the Valles Marineris, the gigantic system of cannons that runs through the Martian equatorial region, to the Acidalia Planitia, on the northern plains. The RSL appear in the warmer times of the year and disappear when the cold returns, something that made you think that could be liquid water. In a note from the U.S. geological Survey, Colin Dundas, researcher of this institution and principal author of the study, argues that the interpretation that the stains have been provoked by dry sand are more compatible with other tests that indicate that the current Mars It's very dry. It is probable that this new study is not the end of the mystery of the RSL and some researchers already argue that the only way to solve the enigma will be that some explorer similar to Curiosity can analyze them on the ground.