Researchers at the University of Arizona have found large amounts of water in the upper atmosphere of Mars, where it is destroyed by photolysis. This partially solves the mystery of the disappearance of water bodies on the planet in the distant past.
Scientists have found that when Mars is closest to the Sun, the planet heats up, and a large amount of water on the surface in the form of ice evaporates from the surface into the upper atmosphere, where it is lost in space. This happens once every Martian year. At the same time, this process contradicts the classical picture of water loss on the Red Planet, according to which ice turns into gas and is destroyed by the sun’s rays in the lower atmosphere, which does not depend on the season.
On Earth, water loss is prevented by a hygropause – a cold layer of the atmosphere where water vapor condenses. However, on Mars, hygro-pause temperatures are high enough to allow steam to rise further, and in the upper atmosphere, water molecules are destroyed within four hours. This process explains the loss by Mars of the ocean layer a billion years ago, almost half a meter thick. An additional 17 centimeters were lost due to dust storms, which intensify the rise of water into the upper atmosphere.
One global dust storm, lasting 45 days, releases as much water into space as Mars would lose in a calm Martian year of 687 Earth days.
However, this process might not have worked more than a billion years ago, as Mars could have had a more pronounced hygropause. At the same time, the planet, most likely, by this time has already lost a large amount of water, which is explained by other mechanisms.