Scientists have shown that regional dust storms play an unexpectedly huge role in the loss of water by Mars, warming the cold Martian atmosphere at high altitudes and preventing the freezing of water vapor. As a result, water molecules reach the rarefied layers of the gas envelope, where they decompose into hydrogen and oxygen under the influence of ultraviolet radiation. This is reported in an article published in the journal Nature Astronomy.
The researchers believed that Mars lost most of its water in large part due to dust storms. Still, they did not realize the role of the significant impact of regional dust storms that occur almost every summer in the southern hemisphere of the planet. Global dust storms that cover the entire planet and occur every three to four Martian years were considered the main cause, along with the hot summer months in the southern hemisphere, when Mars approaches the Sun at a minimum distance.
The scientists analyzed data obtained by the Mars Reconnaissance Orbiter, which measured the temperature, concentration of dust, and water ice at an altitude of about 100 kilometers above the surface of Mars. Another device – the ESA (European Space Agency) Trace Gas Orbiter -measured the concentration of water vapor and ice. Finally, the NASA Mars Atmosphere and Volatile EvolutioN (MAVEN) space probe measured the amount of hydrogen that breaks off from a water molecule at an altitude of 1000 kilometers above the surface.
The Trace Gas Orbiter spectrometers detected water vapor in the lower layers of the atmosphere even before the dust storm began. Usually, the temperature of the Martian atmosphere gets colder with altitude during most of the Martian year, which means that the water vapor rising in the atmosphere freezes at relatively low altitudes. But when the dust storm began, the water vapor reached great heights. The instruments detected 10 times more water in the average atmosphere after the start of the dust storm, which exactly coincides with the data from the Mars Reconnaissance Orbiter.
It is expected that at high altitudes, water vapor is split into hydrogen and oxygen under the influence of ultraviolet radiation from the Sun. MAVEN observations confirmed this by recording the glow of the upper atmosphere caused by hydrogen, the concentration of which increased by 50 percent during the storm.