Geologists have found evidence that many clay deposits on the surface of Mars did not arise from eruptions of hot geysers, but due to the unusual interaction of the planet's primary atmosphere and its rocks, according to an article published in the journal Nature.
“One of the main mysteries of Mars' early history is that we cannot explain how such large deposits of clay and other sedimentary rocks appeared on its surface, which can be seen on images from probes and rovers. Our theory eliminates all these problems,”said John Mustard of Brown University in Providence (USA).
Until recently, scientists were not aware of any reliable traces of the existence of water on the red planet in the past or today. In March 2013, the Curiosity rover discovered the first traces of water in the form of deposits of clay, which it found by drilling a rock called "John Klein" at one of its first sites.
Subsequently, scientists found many other deposits of clay and other evidence that Mars had fresh, habitable water. According to planetary scientists today, Gale Crater, where the rover is today, is the bottom of a giant dry lake, sediments from the bottom of which cover the crater and its central part - Mount Sharp.
These discoveries, as well as images from the Mars Odysseus and MRO probes, indicating the presence of huge deposits of other sedimentary rocks from the phyllosilicate class, have led scientists to wonder how these clay reserves might have originated. Liquid water, if it was present on Mars, could have existed on its surface for an extremely short time, several hundred million years, and, as climate models show, it could hardly have generated such large amounts of clay.
Mustard and his colleagues found a simple explanation for this early enigma of Mars by creating a computer model of the early red planet, when it did not yet have an atmosphere and no reserves of liquid or frozen water.
Scientists drew attention to the fact that its bowels, as shown by the analysis of the contents of Martian meteorites, contain large amounts of water and other volatiles that should have been actively eroded from the rocks at the moment when Mars was a hot ball of lava.
These vapors should have formed a rather thick and dense primary atmosphere, a kind of "steam bath", the interaction of which with the cooling crust of Mars, as geologists suggested, could generate large reserves of clay in the first 20 million years of the planet's existence.
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They tested this idea by trying to reproduce this process in the laboratory. For this, scientists created an analogue of the primary atmosphere of Mars, heated it and immersed a piece of basalt in it, similar in its properties to the matter of the red planet. The results of these experiments surpassed all the expectations of scientists - in just two weeks they found that a significant part of the "Martian" matter turned into a kind of clay.
The success of this experiment, according to the authors of the article, shows that a significant part of the primary Martian crust, about 10% of its total mass, could have turned into clay in the first moments of the existence of Mars. Most of these deposits were buried by volcanic eruptions, but even a small fraction of these "primary clays", as scientists call them, would be enough to explain the reserves of phyllosilicates and other sedimentary rocks that were found by rovers and probes.
“It would be especially interesting to test our idea with the instruments of the Mars 2020 rover. If NASA decides to plant it in a suitable place for us, then we can get the clay samples we need and confirm or disprove our theory,”the scientist concludes.