Chemical composition as an indication
Most of the water that could once have covered all of Mars to a depth of 100 to 1500 meters is likely to be bound in minerals and clay and consequently trapped under the dust-dry Martian soil. This knowledge is based on a chemical analysis of the current Martian atmosphere and the Martian surface. The atmosphere would have to have a much higher proportion of deuterium if the water had been lost almost exclusively through the atmosphere.
Earth as a model
It is not far-fetched that water can be stored and trapped in minerals and other substances such as clay through the interaction with rock and the chemical processes that take place. This process is also well documented on earth, but due to the tectonic plate shifts and volcanism, these water-containing minerals are melted again and the water is partially released again.
However, since Mars has no tectonic plates, the “drying out” through this process is permanent compared to the earth. Given the enormous amounts of water that were calculated for Mars at an earlier stage, the researchers assume that both factors played a role. So, the binding of the water in the crust as well as the loss of the water to space.
The exciting theory could provide new insights into geology and climate change on Mars. Soil samples and atmospheric measurements by the Mars rover Perseverence should bring new clues. The previous research results were published in the journal Science.