Experimental confirmation of liquid brines on Mars

Abstract:

The discovery of water ice and perchlorates in the shallow subsurface of Mars [1,2] is interesting because they could produce aqueous liquid solutions under Mars’ present-day environmental conditions.

We used the Michigan Mars Environmental Chamber [3] to simulate the pressure, temperature and relative humidity during the full diurnal cycle of sol 19 at the Phoenix landing site. Sol 19 was chosen because on this sol ice found in a shallow trench (Dodo-Goldilocks) at a depth of ~5 cm was removed with little effort [4], suggesting that it was a frozen brine (softer than freshwater ice), and because oblate spheroids found on a strut of the lander, possibly a saline mud, were observed to grow and darken (suggesting liquefaction) [4].

The results of our simulations show that early in the mission the frozen brine likely found in the Dodo-Goldilocks trench could melt in the morning, temporarily forming aqueous liquid solutions when the temperature in the trench was above the eutectic temperature of the Ca(ClO₄)₂ salt (~199 K). In addition, the results of our simulations indicate that the spheroids observed on a strut of the Phoenix lander were most likely droplets of liquid brines.

Since halophilic terrestrial bacteria thrive in brines [5], our results suggest that Mars’ polar region could potentially be a habitat for microorganisms. In addition, it has been suggested that frost could form on fine-grained terrains at Gale crater during the winter [6]. If this frost gets in contact with perchlorate salts, it could melt temporarily forming liquid brines.