H2O at astonishing heights: Scientists have discovered how our once damp neighboring planet is still escaping the water into space. Contrary to previous assumptions, water molecules are also carried into the upper Martian atmosphere, according to data from NASA’s MAVEN probe. There they disintegrate so that molecular hydrogen can then escape into space. According to the results, seasonal effects and dust storms apparently bring the water increasingly to high altitudes. Since when this process has dominated water loss and what significance it had in the development of Mars as a whole remains questionable.
Today it is a frosty desert planet, but it is now certain that Mars was shaped by liquid water in its youth – similar to the earth. But obviously our neighboring planet lost most of its water resources in the course of its evolutionary history. The remains today form the ice caps at the poles as well as small amounts in the underground and in the thin atmosphere. It was already assumed that Mars could not hold its water in the long term: Most of it was broken down into hydrogen by UV radiation over the billions of years, which could then literally easily escape into space.
On the trail of water loss
This process is still drying up Mars today, according to the evidence of hydrogen in the upper layers of the atmosphere. However, models of this process suggested that the water is only converted into hydrogen in lower layers before it rises into the upper atmosphere. Because it was assumed that the water molecules cannot rise above a certain height because they then crystallize out and sink down again. In the case of the earth, this area is called the hygropause. As the results of the researchers working with Shane Stone from the University of Arizona in Tucson now show, Mars, in contrast, no longer has a pronounced hygropause.
The results are based on evaluations of data from NASA’s MAVEN probe. As it orbits Mars, it regularly plunges into the planet’s upper atmosphere. An analytical instrument can record the concentration of substances – including water molecules. As the researchers report, they have now been able to detect water at a surprisingly high altitude of around 160 kilometers above the surface of Mars. Once they arrive in the upper atmosphere, the calculations show that the water molecules are then broken apart very quickly by ions. The resulting atomic hydrogen is then lost into space.
Dust storms have a particularly drying effect
As can also be seen from the evaluations, the extent of the water vapor rise is linked to the season and the dust storms on Mars. Compared to Earth, our neighboring planet orbits the sun in a somewhat more elliptical orbit and comes closest to it during the summer in the southern hemisphere. As the scientists explain, Mars heats up the most during this time, which is apparently linked to the increased mobilization of water from the surface. The annual regional storms, as well as the major global dust storms that swirl across the planet roughly every ten years, further warm the atmosphere and increase the upward movement of water, the scientists say. According to them, there are signs that global dust storms can increase the transport of water to the upper atmosphere by 20 times. According to this, a global dust storm that lasts 45 days releases the same amount of water into space as Mars would lose during a quiet year.
“The loss of its atmosphere and water to space is one of the main reasons that Mars is cold and dry today compared to the warm and humid Earth. The new data from MAVEN now show a process by which this loss still occurs today, ”says Stone, summing up the results. This process may have played a major role in the drying up of the planet. When the researchers projected the data over the last billion years, they came up with a considerable loss of water: “If we took the water that has been deflated by the seasonal process and distributed it evenly over the entire surface of Mars, a global ocean would be created with a water depth of about 44 centimeters. The effect of global storms would make an additional contribution of around 17 centimeters, ”says Stone.
However, as the researchers emphasize, it remains unclear what role the process played in the overall loss of water on our neighboring planet. Because the hygropause effect of Mars was probably stronger earlier due to its once denser atmosphere. “Before the process we are describing started, there must have been a significant amount of atmospheric leakage into space,” says Stone. “We have to sound out the effects of this process and the point in time at which it began to function even more precisely,” says the scientist.
Source: University of Arizona. Articles: Science, doi: 10.1126 / science.aba5229