The past presence of liquid water on Mars has long been in doubt, but the Mars rover Curiosity continues to document traces of it, still visible billions of years after its disappearance. Witness the images taken recently by the NASA machine, during its ascent of Mount Sharp and made public on February 8 by the American space agency. One of them shows ripples on the surface of the Martian ground, like those that would be left by wavelets agitated by the wind at the edge of a shallow expanse of water.
“This is the best evidence of water and waves we have seen in the entire mission”estimates, in a press release, Ashwin Vasavada, chief scientist of the Curiosity mission at the Jet Propulsion Laboratory (Pasadena, California), which coordinates the peregrinations of the rover. “We have climbed hundreds of meters of lake deposits and have never seen such evidence – and now we have found some in a place we thought was dry. »
Climbing Mount Sharp is also a journey through time, with the higher layers corresponding to more recent and therefore drier times in the history of the Red Planet. Since 2014, Curiosity has been climbing the foothills of this structure nearly 5 kilometers high, and has risen some 800 meters, moving away from the youth of Mars where this relief was crossed by rivers and bathed in lakes. So much so that the researchers did not think they would come across such traces of a body of water at this altitude. The ripples that had been stuck in the sediment for billions of years were too tough for Curiosity’s drill to break through.
“Wonderful complexity”
Nearby, in a depression called Gediz Vallis, the rover’s cameras also saw accumulations of boulders and rock debris, some the size of cars, that may have been brought there by wet landslides. Mission officials are hoping their protege can get close, as they may have tumbled from heights of Mount Sharp – and therefore from more recent times – that he won’t have the opportunity to reach.
Finally, the NASA press release mentions a third geological structure of interest, rocks composed of alternating regular layers, whose terrestrial equivalents refer to periodic meteorological or climatic phenomena. “The ripples, debris flows and rhythmic layers tell us that the story of the transition from wet to dry on Mars is not a simple one”indicates Ashwin Vasavada. “The ancient climate of Mars had a wonderful complexity, much like that of Earth. »