The last remnants of Martian rivers and oceans might not have evaporated into space, but literally soaked into its rocks and changed their chemical composition, turning the planet red, according to an article published in the journal Nature.
“The circulation of rocks in the bowels of the Earth prevents abrupt changes in the concentration of water on the planet's surface, since the 'excess' moisture is removed from the rocks before they reach the mantle. It does not exist on Mars, and its waters constantly interacted with “dry” basaltic lavas to form water-rich minerals. As a result, the appearance of Mars changed, and the planet became dry and lifeless,”said Jon Wade of the University of Oxford (UK).
In recent years, scientists have found many hints that rivers, lakes and whole oceans of water existed on the surface of Mars in ancient times, containing almost as much liquid as our Arctic Ocean. On the other hand, some planetary scientists believe that even in ancient times, Mars could be too cold for the permanent existence of oceans, and its water could be in a liquid state only during volcanic eruptions.
Recent observations of Mars with ground-based telescopes have shown that over the past 3.7 billion years, Mars has lost an entire ocean of water, which would be enough to cover the entire surface of the red planet with an ocean 140 meters thick. Where this water disappeared, scientists today are trying to figure out by studying ancient Martian meteorites.
Wade and his colleagues drew attention to one interesting feature of the oldest Martian meteorites - their rocks are completely different neither in color, nor in structure and composition to the minerals that Curiosity and Opportunity rovers find on the surface of Mars today. In particular, they contain a large number of so-called basic rocks, and extremely few compounds with a large number of oxygen atoms and other oxidizing agents.
This prompted them to believe that the chemical composition of rocks on Mars could have changed noticeably in the last 4 billion years under the influence of cosmic rays, solar wind and liquid water, large reserves of which should have been present on the planet at the time these meteorites "catapulted".
Guided by this idea, scientists analyzed how water could interact with rocks, analogues of which are found in meteorites, and calculated the volume of water that they could absorb and hold inside themselves as they dive into the bowels of Mars. This allowed them to understand where his water had disappeared and to find the main "culprit" of this loss - iron oxide.
As scientists have found, Martian basalts and other basic rocks will absorb and interact with water much more actively than their “cousins” from Earth, since they contain almost twice as much iron oxide as similar minerals on our planet. Thanks to this, the bowels of Mars turn into a kind of sponge that constantly absorbs water and almost does not return it back due to the fact that there is no tectonics on the red planet.
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As a result, most of the waters of Mars, according to Wade, did not evaporate into space, as most planetary scientists believe today, but "flowed" into its bowels, where it is still hiding. The next NASA rover, the authors of the article hope, will help test whether this is the case or not.