Hydration/ dehydration behavior of minerals under Mars-relevant conditions

A key element to predicting the potential for life on Mars is understanding the availability of water, the universal requirement for all life as we know it. The limited stability of liquid water on the martian surface suggests that any life on Mars would be forced to make use of unusual water sources in the absence of bodies of water, as are found on Earth. The aim of this work is to understand processes that occur with changes in temperature (T) and relative humidity (RH) during a Mars sol that have the potential to influence the (bio)availability of water and potentially affect the atmospheric H2O concentration. Data in the literature and new field measurements at an analog site in New Mexico, USA, were used to determine what minerals would be relevant to Mars and which could occur on the surface, making them available to interact with the atmosphere. More specifically, this work focuses on several hydrous salt systems' potential for interaction with the martian atmosphere. Many salt systems have hydration and dehydration reactions that occur within relevant RH/T conditions and on the time scale of a martian sol, yielding the potential for significant participation in the H2O cycle of Mars. Several systems were investigated via time-resolved X-ray diffraction at varying RH, T, and rates of change. Experiments were carried out under simulated martian conditions using three minerals determined to be relevant: blodite (Na2Mg(SO4)2·4H 2O), bischofite (MgCl2·6H2O), and kainite (KCl·MgSO4·3H2O). These measurements identified several previously unknown phases, as both the Na2Mg(SO4) 2·nH2O and MgCl2· nH2O systems reacted to new phases under low-humidity, low-temperature (< 0° C) conditions. In addition, the MgCl2· nH2O, Na2Mg(SO4)2· nH2O, and KCl·MgSO4· nH2O systems reacted at T > 25° C, yielding information about dehydration reactions that may occur under the low-PH2O conditions of Mars. The crystal structures of the kainite reaction product ( n = 2) at T > 25° C and blodite's reaction product at sub-ambient T (n = 16) are both described herein. Together, the low- and elevated-T phases identified in these studies all have the potential to interact with the martian atmosphere and participate in the daily martian H2O cycle, thereby affecting the availability of water on the surface.