Previously observed changes to the surface of Mars may be the result of liquid water boiling under the low pressure of a thin atmosphere, according to a study published online this week in Nature Geoscience.
Under the low atmospheric pressure at the Martian surface, water is not stable as a liquid and will either quickly freeze or boil, meaning liquid water exists only temporarily. The streaks that have been seen to appear and lengthen on slopes during the Martian summer have been attributed to the action of flowing salty (briny) water, yet it is unclear how the temporary flow of small amounts of water might cause these surface changes.
Marion Masse and colleagues conducted a series of laboratory experiments on Earth in a Mars Chamber facility to observe how water interacts with sediment under simulated Martian surface conditions. They placed an ice block on top of a slope made of sand and observed how the resulting meltwater percolated downslope through the sand. Under Earth-like conditions, they observed little change to the slope due to the trickle of water. However, under Mars-like lower air pressures, they found that the water boiled and caused the ejection of sand grains, with grains piling up until the piles collapsed. The authors found that, in the experimental slopes, this process formed small channels that resembled those observed on Mars, suggesting that a similar process may be at work on the Red Planet.
In an accompanying News & Views article, Wouter Marra writes that, “instead of requiring the stability of substantial water or brines, it is the instability of water on Mars that may explain the morphological activity needed to form the observed features.”