The Rover Perseverance has just landed on Mars. Meanwhile, its forerunner Curiosity continues to explore the foothills of Mount Sharp (officially Aeolis Mons), a mountain several kilometers high in the center of Gale Crater. Using a telescope on the ChemCam instrument for detailed observations of the steep Mount Sharp terrain at a distance, a French-American team led by William Rapin, a CNRS researcher at the Institute of Astronomy and Planitology (CNRS / Université Toulouse III / CNES), found that there the recorded Martian climate alternated between the arid and wetter periods, before drying out completely about 3 billion years ago.
Spacecraft in orbit around Mars have already provided indications of the mineral composition of the slopes of Mount Sharp. But now ChemCam has successfully made detailed observations of sedimentary troughs from the planet’s surface, revealing the conditions under which they formed. Moving through the observed terrain, which is several hundred meters thick, the types of riverbeds change radically. Lying above the lake of stacked clays that form the foot of Mount Sharp, the wide, high, transversely covered structure is a sign of the migration of winds formed by the dunes during the long dry climate episode.
Worse, thin alternating brittle and resistant troughs are typical of floodplain deposits, marking the return of wetter conditions. The climate of Mars therefore probably suffered several large fluctuations between dry conditions and the river and lake environment, until generally dry conditions prevailed today. During his extended mission, Curiosity should climb to the foot of Mount Sharp and break into different beds. They will test this model, characterize in more detail how the ancient climate developed, and possibly understand the origin of these major fluctuations.
Note: Other team members work in the Laboratory of Geology of Lyon: Terre, Planètes, Environment (CNRS / ENS de Lyon / Claude Bernard Lyon University 1) and the Laboratory of Planétologie et Géodynamique (CNRS / Université de Nantes / Université d ‘Angers) in France; at UC Santa Cruz, U.S. Geological Survey, California, Los Angeles Institute of Technology, and National Laboratory in the United States.
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