Results from NASA's Mars Curiosity rover have shown that salty liquid water could exist just beneath the surface. Analysing the Martian soil, NASA’s rover found a substance known as calcium perchlorate - a salt that can prevent water from freezing by lowering its freezing point. This perchlorate could absorb water vapour in the planet's atmosphere, forming a salty brine that would seep down into the soil.
“When night falls, some of the water vapour in the atmosphere condenses on the planet's surface as frost,” says Dr Morten Bo Madsen, head of the Mars Group at the University of Copenhagen's Niels Bohr Institute, “but calcium perchlorate is very absorbent and it forms a brine with the water, so the freezing point is lowered and the frost can turn into a liquid.”
Curiosity found the calcium perchlorate whilst making its way towards Mount Sharp, a 5.5km-high mountain in the Gale Crater near to where the rover landed in August 2012. Since then, Curiosity has travelled over 10km from its landing site towards the mountain, carrying out numerous studies along the way.
As well as finding perchlorates, Curiosity also used its camera to spot layers of sedimentary deposits inside the crater. “These kinds of deposits are formed when large amounts of water flow down the slopes of the crater and these streams of water meet the stagnant water in the form of a lake,” explains Madsen. “The sediment plates on the bottom are level, so everything indicates that the entire Gale Crater may have been a large lake."
Although Curiosity has now revealed that liquid water might still exist on Mars, don't hold your breath for any little green men. Unfortunately, the planet is too dry, too cold and has very little protection from the cosmic radiation that continually bombards it, making complex life very unlikely indeed.