My interpretation of the article "Spectral evidence for hydrated salts in recurring slope lineae on Mars" - Nature Geoscience 28 Sep 2015
Water is essential to life as we know it here on Earth. The presence of liquid water on Mars today has implications for geology, hydrology, the study of the origins and distribution of life in our solar system and beyond, and also for human space exploration.
While the average temperature on Mars is less than -50 degrees Celsius, temperatures of up to 27 degrees Celsius can occur during warm seasons. On certain slopes of terrain, narrow streaks have been observed to appear and grow during these warm periods. A solution of salts in water can lower the freezing point of water by up to 80 degrees Celsius, thereby significantly lowering the evaporation rate of water, and thus increasing the possibility of forming and stabilising liquid water on the surface of present-day Mars.
Brine- a solution of salt in water- has therefore been proposed to explain these streaks, however, no evidence of water or such salts has yet been found. Now, spectral data from the Mars Reconnaisance Orbiter (MRO) has found hydrated salts at all four locations where streaks were observed on the surface of Mars, probably magnesium perchlorate, magnesium chlorate and sodium perchlorate.
These findings strongly suggest that seasonal warm slopes are currently forming liquid water on Mars. While the possible origins of this water are not yet understood, a variety of formation mechanisms in different locations on the planet may be taking place. With respect to the search for microbial life on Mars, this discovery means we will be working hard to further characterise and explore these unique regions of Mars.
While it is good news for planned human settlements on Mars that there may be liquid water present, COSPAR and the Outer Space Treaty aim to protect extra-terrestrial bodies to make future science investigations possible, and in particular to prevent contamination by Earth life of unique areas where extra terrestrial life may exist. So it is likely that these areas where liquid water may be flowing will be out of bounds for human settlement until careful and detailed astrobiological investigations have been made in these areas.
But excitingly, as a result of investigating these unique locations supporting liquid water on Mars, in the next few years we could make one of the most profound discoveries in the history of life on Earth- the discovery of life on another planet.