Mars has just revealed a new secret: frost has been detected at the top of its gigantic volcanoes, an unexpected discovery which will allow a better understanding of the water cycle of the red planet, essential for future explorations.
The scene was captured by chance from Martian orbit by the Trace Gas Orbiter (TGO) probe of the European Space Agency (ESA), in the Tharsis dome near the equator of Mars, describes a study published Monday in Nature Geosciences.
It is a vast elevated region, approximately 5,000 km in diameter, housing immense volcanoes, extinct for millions of years. Among them, the largest in the solar system, Olympus Mons and its 22 km high – three times Everest.
No one expected to find frost there. “We thought it was impossible around the equator of Mars,” summarizes Adomas Valantinas, the first author of the study behind the discovery.
Strong sunshine and very low atmospheric pressure “keep temperatures at a fairly high level at the summits and on the surface,” explains this researcher at Brown University in the United States, in an ESA press release.
In the Tharsis region, temperatures can drop very low – as low as – 130 degrees at night – but they do not depend on altitude, “unlike what happens on Earth, where we expect to see frozen summits,” he analyzes.
The atmosphere of the Martian equator is, moreover, particularly low in water, which makes condensation difficult. “Other probes had observed frost but in wetter regions, notably the northern plains,” Frédéric Schmidt, professor at Paris-Saclay University, one of the authors of the study, explains to AFP.
The thickness of a hair
The discovery was therefore fortuitous. The TGO probe, which has been orbiting Mars since 2018, has the advantage of being able to observe its surface at all hours of the day, notes the planetologist specializing in ice in the solar system.
She was thus able to take images when the first rays of the sun arrived. “We saw a shiny, blue deposit there, a particular texture that we only see in the early morning and in the cold seasons,” he says.
You had to have a keen eye as the ice deposit is thin – the thickness of a hair – and the phenomenon is furtive. But the quantity of frost present at the summits of four volcanoes (Olympus Mons, Ascraeus Mons, Arsia Mons and Ceraunius Tholus) represents “150,000 tons of water circulating between the surface and the atmosphere every day, the equivalent of 60 swimming pools Olympic Games,” comments the ESA.
How to explain it? The study authors suggest the existence of a microclimate inside the volcanoes’ calderas, their vast circular craters. The winds would move up the slopes of the mountains, “bringing relatively humid air close to the surface to higher altitudes, where it condenses and is deposited in the form of frost,” says Nicolas Thomas, co-author of the study.
“We observe this phenomenon on Earth and in other regions of Mars,” adds the principal investigator of TGO’s Color and Stereoscopic Surface Imaging System (CaSSIS).
Modeling the process of frost formation should allow us to better understand the water cycle – its dynamics of movement between the surface, the atmosphere, the equator and the poles – “one of the best kept secrets” of the red planet, according to the ESA.
An important step for future human and robotic explorations. “We could recover water from the frost for human consumption, and launch rockets from Mars by separating the molecules of oxygen and hydrogen,” anticipates the Pr Schmidt.
Being able to map water on the Martian surface – which currently only exists in the form of vapor or ice – is also ultimately essential to the quest for traces of life, the appearance of which would have been made possible by the presence of liquid water, between 3 and 3.5 billion years ago.