Could Mars once have been a wet, green planet, covered in rain and landscapes similar to Earth’s rainforests? A new study, published at the beginning of December, suggests this, based on the discovery of “bleached” rocks on the surface of Mars, associated with hot and rainy climatic conditions which would have persisted for millions of years.
The fragments were identified by NASA’s Perseverance rover during its exploration of Jezero Crater, a 45-kilometer-long ancient impact basin that hosted a lake of liquid water billions of years ago. The first images and analyzes carried out by the SuperCam and Mastcam-Z instruments made it possible to compare the material with similar formations found on Earth.
The rocks are composed of kaolinite, a white clay mineral that, on Earth, forms in very humid tropical environments, after long periods of intense rain that “wash” other minerals from the rocks. For scientists at Purdue University in Indiana, the presence of this type of material on Mars is a strong indication that the planet once had a climate similar to regions such as the Amazon rainforest and forested areas of West Africa.
Professor Briony Horgan, an expert in planetary science and one of the study’s authors, classified the fragments as “probably among the most important outcrops ever observed” on Mars. She says the evidence points to an ancient environment that was “warmer and wetter, where it rained for millions of years,” a scenario considered favorable for the emergence and maintenance of life.
The researchers point out that there are no large kaolinite formations nearby that could easily explain the origin of these fragments, suggesting that they were transported by ancient rivers feeding Lake Jezero or even thrown into the crater by meteorite impacts. In either case, the rocks would be direct records of a period when water was abundant and active on the Martian surface.
The contrast with modern-day Mars makes the discovery even more significant. Today, the planet is cold, dry and dusty, with an extremely thin atmosphere composed of about 95% carbon dioxide. Water exists primarily as ice below the surface, particularly in polar regions, in addition to small seasonal flows of brackish water on slopes and crater walls.
According to NASA estimates, around 4.3 billion years ago, Mars would have had enough water to cover its entire surface with a layer approximately 137 meters deep. By 3.5 billion years ago, this water was most concentrated in lake and river systems, and the last major episodes of liquid water at the surface may have occurred around 2 billion years ago, before the significant loss of the atmosphere.
The new work, published in the journal Communications Earth & Environment on December 1, reinforces the idea that Mars had a complex aquatic past, with deltas, lake beds and networks of river valleys. As summarized by the US space agency itself, the planet contains rocks and minerals that could only have formed in the presence of liquid water, as well as evidence of massive floods around 3.5 billion years ago.
For scientists, the kaolinite rocks scattered along Perseverance’s path are today one of the most concrete proofs that the Red Planet was, at one point in its history, a potentially habitable world, very different from the icy desert we observe today.
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