Boiling saline water on Mars may have caused the mysterious ridges seen on the surface of the red planet, say scientists who discovered the exotic process unknown on the Earth.
At present, liquid water on Mars only exists in small quantities as a boiling liquid, and only during the warmest time of day in summer. Its role has therefore been considered insignificant.
However, scientists from National Centre for Scientific Research (CNRS), Universite de Nantes and Universite Paris-Sud in France have shown that water that emerges onto the surface of Mars immediately begins to boil, and creates an unstable, turbulent flow that can eject sediment and cause dry avalanches.
The flow of small amounts of a boiling liquid therefore significantly alters the surface.
The discovery of this exotic process, unknown on our planet, radically changes our interpretation of the Martian surface, making it difficult to undertake a direct comparison of flows on the Earth and on Mars.
It is well known that water boils at 100 degrees Celsius. But on Mars, where the atmosphere is much thinner than on Earth, it can boil at temperatures as low as 0 degree Celsius.
During the Martian summer, when the subsurface water ice begins to melt and emerge at the surface, where the mean temperature reaches 20 degrees Celsius, it immediately starts to boil.
To find if an evaporating liquid alter the Martian landscape, researchers used a former diving decompression chamber to reproduce the low pressure of the Martian atmosphere.
At the same time, another team carried out the same experiment in a cold chamber at Earth's atmospheric pressure.
In both chambers, a block of pure water ice, followed by one of saline water ice, were melted at 20 degrees Celsius (as on Mars in summer) on a sand-covered slope.
The experiments showed that, in the flows produced under terrestrial conditions, the water gradually seeped into the sand, leaving no trace on the surface after drying.
However, in the Martian chamber, the water produced by the melting ice started to boil as soon as it reached the surface, and the gas released caused the ejection of sand grains.
These gradually formed small ridges at the front of the flow, which, as they grew larger, became unstable and actually produced avalanches of dry sand.
The process was even more violent at lower pressures. The surface, once dry, exhibited a series of ridges.
This process is not as efficient in the case of saline water since it is more stable than pure water under Martian conditions.
However, since saline water is more viscous, it can carry along sand grains and form small channels, a process that can sometimes become explosive under low pressure.
The findings were published in the journal Nature Geoscience.
