A study by the INGV has highlighted, on some Martian dunes, the seasonal appearance of water that we may have observed for the first time in a liquid state
The presence of liquid water on Mars could be the cause of a rare phenomenon observed on the dunes of the Red Planet: this is what emerges from the study “Geomorphological Observations and Physical Hypotheses About Martian Dune Gullies” conducted by researchers fromNational Institute of Geophysics and Volcanology (INGV) and recently published in the magazine Geosciences of MDPI.
At least 3.7 billion years ago, Mars had a much denser atmosphere than it does today and hosted lakes and oceans: over time, much of the planet's atmosphere has been lost, making it almost impossible, due to the extremely low atmospheric pressure, for stable liquid water to exist on its surface.
The research conducted by INGV analyzed the leeward side of the Russell dune, the largest of the dunes formed by the wind inside the homonymous Martian crater, focusing on the behavior of water in the atmospheric conditions of temperature and pressure of the Red Planet.
“The analysis of 110 very high resolution images (up to 25 cm/pixel) collected over 8 Martian years (or approximately 16 Earth years) by the US Mars Reconnaissance Orbiter probe has allowed us to highlight for the first time the possible presence of water on Mars at its triple point, or in an equilibrium capable of allowing the physical states of solid, liquid and vapour to coexist, highlighting a recurring seasonal cycle”, explains Adriano Nardi, researcher at INGV and first author of the article. “Even if for short periods, in the first days of the Martian spring and during gusts of wind, every year on this dune water can appear in atmospheric conditions of temperature and pressure that allow its transient appearance in the liquid state".
The water, in this case, would be produced by a meteorological phenomenon typical of the Martian environment which manifests itself near the surface of the dunes thanks to their aerodynamic shape, impossible to reproduce on Earth where, moreover, the characteristic dune gullies of Mars have never been observed (gullies).
“The genesis of the 'classic' Martian gullies had been investigated by a previous study of ours, which highlighted how spring water could produce those gullies through the seasonal melting of permafrost, or ice trapped in the ground in past eras. This new research, however, has identified even rarer phenomena that produce channels different from the classic ones, called 'linear gullies' due to their more linear shape”, he adds Antonio Piersanti, Research Director of INGV and co-author of the study.
"Linear gullies may be formed by frost which, thanks to the images of the Mars Reconnaissance Orbiter probe, we have highlighted on the top of the Russell dune. The surface of the slope is laterally undulating and, when the channels remain in the shadow, they are observed traces of humidity absorbed by the sand. Conversely, when a channel turns in the direction of the light, we witness theimmediate evaporation of water which had remained liquid up to that point”.
Under normal conditions, the Martian environment could support the presence of ice. However, this would be dry ice, which can change state only by turning into vapor, and vice versa. With this study, the effects of water present simultaneously in its three states were exceptionally observed, even if the liquid state is the least stable.
“This could be the first time ever that liquid water has been observed on Mars: it is certainly the First time the formation and morphology of a rare Martian phenomenon are associated, the linear gullies present on its dunes, to the action of liquid water in the current environment", concludes Nardi.
If confirmed, the presence of liquid water, even for very short periods, could have significant consequences for understanding Martian geology and for search for microbial life forms, as well as for the identification of landing sites for future space missions on Mars.
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figure The image in the center shows the leeward side of the largest of the dunes formed by the wind inside the Russel crater. On this side we can see traces of the so-called “linear gullies”. At the top of the slope we can observe a possible source constituted by frost (magnification B). The surface of the slope is laterally undulating and when the channels turn in the direction of the pole (remaining in the penumbra) we can observe traces of humidity absorbed by the sand (magnification U). When instead a channel turns in the direction of the light (magnification V) we can observe the immediate evaporation of the water that had remained liquid up to that point. On the same side we can observe various phenomena similar to avalanches that trace or deform the channels (as highlighted in the circle) and at the end of the channels it is possible to find large rounded blocks of ice (magnification G) that can reach the size of a small car.
(Processed on HiRISE/MRO image: ESP_047078_1255 - NASA/JPL-Caltech/UArizona)
Active gullies on Russell Dune (Processed on HiRISE/MRO image: ESP_047078_1255 – NASA/JPL-Caltech/UArizona)
Water state diagram in relation to the surface environments of Earth (in green) and Mars (in orange). The relative surface levels are indicated for guidance.