Blue on Red: Chemical conditions of liquid water emerging on simulated Martian regolith

There is evidence of large subglacial reservoirs of liquid water on Mars, while the debate continues on whether any surface water intermittently flows following the subsurface ice melting in selected locations. The chemical conditions of waters that could be present on Mars were previously subject to modeling studies or experimental research that did not involve perchlorates which are known to be present in Martian regolith. Therefore, the present experimental research aimed to understand the chemistry of water incubated for 21 days with the Martian regolith simulant MGS-1 mixed with different levels of perchlorate (0.25-1.0% corresponding to 1.5-6.0mM ClO4- ions). The dissolution of chemical compounds from MGS-1 was rapid with electric conductivity (EC) in the 1.8-2.3 mS/cm range after 1 h incubation. Throughout the experiment, fluctuations of pH, EC and oxidation-reduction potential were observed, although generally, the water was rich in ions, highly oxidized and had a circumneutral pH. Dominant elements included S, Mg, Ca, Na, K and Fe. Two patterns of element concentrations were observed: (1) a rapid increase with a peak 3 h after flooding the regolith and then a gradual decrease indicating adsorption and immobilization (Al, Cr, Fe, Si and Ti), and (2) a gradual increase in concentration throughout the experiment (Ca, K, Mg, Na and S). The presence of perchlorate in the simulant did not affect the general patterns of water chemistry parameters, although it appeared to enhance the leaching out of Mg, Na, S (with max concentrations noted in the presence of 1.0% perchlorate), Al, Ca (0.5%) and Cr, Fe, Si and Ti (0.25%). No detectable concentrations of Mn and P were leached from the regolith simulant throughout the experiment. This study provides a pilot experimental overview of the complex physicochemical conditions that modern liquid water on Mars could present with the potential implications for the survival of biological life and use as an in situ resource.

Automated summary

This study experimentally investigates the chemistry of water mixed with different levels of perchlorate in Martian regolith simulant. The presence of perchlorate does not significantly affect the general patterns of water chemistry parameters. The results provide important insights into the physicochemical conditions of modern liquid water on Mars and its potential implications for biological life and resource utilization.