Fig. 2: Deliquescence-induced brine formation at the Phoenix landing site and Gale Crater.
From: Cryogenic origin of fractionation between perchlorate and chloride under modern martian climate
a In situ RH-T data of the Phoenix landing site are overlaid onto the deliquescence surfaces of the salt mixtures. I: Mg(ClO4)2•6H2O + MgCl2•12H2O; II: Mg(ClO4)2•6H2O + MgCl2•8H2O; III: Mg(ClO4)2•6H2O + MgCl2•6H2O; and IV: Ca(ClO4)2•6H2O + CaCl2•6H2O. The dark gray regions are the projection of the ternary deliquescence surfaces, and the dark cyan and dark red horizontal lines are the projections of the lower- and upper- T boundary planes, respectively, as shown in Fig. 1. The green dots are in situ RH-T measurements. The thick solid dark-cyan curve is the best fit line, and the thin dashed dark-cyan curves are the 10 K uncertainty boundaries. Salt mixtures of Mg(ClO4)2•6H2O-MgCl2•6H2O and Ca(ClO4)2•6H2O-CaCl2•6H2O may facilitate the formation of brines with elevated ClO4−/Cl− signatures. b In situ RH-T data of Gale Crater overlaid on the deliquescence surfaces of the salt mixtures. The dark gray ternary deliquescence surfaces and the lower- and upper- T boundary lines of subfigures I to IV are the same as shown in (a). The colored dots are the in situ RH-T data (REMS; sols 526, 531, 548, 549, 551, and 554 to 561 with maximum yearly humidity). The RH-T conditions of the first Martian year at Gale Crater would support the deliquescence of Ca(ClO4)2•6H2O-CaCl2•6H2O but not for any of the Mg salt mixtures.
