At this stage of our understanding of the planet Mars, we have seen salty water flowing (recurring slope lineae), found evidence of ancient riverbeds, and seen seasonal changes in the polar caps. But an important question is how does water behave on Mars? A bit of science here on Earth gives some insight.
Water at sea level on Earth boils at 100 degrees Celsius, which actually defined the Celsius scale. But as pressure changes, liquids boil at different temperatures. As the atmosphere gets thinner, the boiling temperature of water decreases. On Mars, with it’s extremely thin atmosphere, this means that water can boil at zero degrees!
Now most of Mars is typically below zero, but during the Martian summer, temperatures often go above zero and can go as high as 20 Celsius, more than warm enough to boil water. The warm temperatures also start to melt frozen groundwater, and then once it reaches the surface, it boils instantly.
So what does all this do to Mars? Well, an international team including scientists from the CNRS, Université de Nantes and Université Paris-Sud and headed by Marion Massé, from the Laboratoire de Planétologie et Géodynamique de Nantes (CNRS/Université de Nantes) have shown that this boiling water dramatically alters the terrain, even causing avalanches.
They carried out two experiments here on Earth, simulating the atmospheres of Earth and Mars at 20 degrees Celsius. In each simulation, a block of normal water ice and salty water ice were allowed to melt down a slope covered in sand. In the Earth conditions, the water soaked the sand as it trickled down the slope, before being absorbed and drying out, with little to no effect on the appearance of the sand slope. The Martian conditions provided a fascinating result. The water boiled as soon as it reached the surface of the sand, bubbling and producing ridges as sand grains were scattered. The ridges continued to form and grow, causing small avalanches, permanently altering the appearance of the slope.
This has opened up another avenue for studying the surface morphology of Mars, and locating the places along the surface where liquid water is prevalent. Finding these key sites are important for future Mars missions and the search for conditions conducive to life.