Extended Data Fig. 3: Phase diagram of calcium perchlorate.
From: Distribution and habitability of (meta)stable brines on present-day Mars
In Figures 2 and 3 we showed results for the (meta)stability of brines formed by the deliquescence of calcium and magnesium perchlorate. Here we show the thermodynamically stable (area shaded in dark grey) and metastable (area shaded in light grey) regions of a calcium perchlorate brine in the typical phase diagram. A brine can form between the ice line (that is, RHice = 100%), here the blue solid line, and the temperature-dependent deliquescence relative humidity (DRH), here shown as the green solid line. However, experiments have shown that metastable solutions exist beyond RHice = 100%, up to RHice = 145%, here shown as the orange solid line. Furthermore, although thermodynamically a solution should efflorescence once conditions fall below the DRH, experimental work has shown that solutions persist until much lower relative humidities are reached (that is, the efflorescence relative humidity, here the red solid line). Non-shaded regions on this plot are conditions that would not permit for stable or metastable solutions of calcium perchlorate. The eutectic temperature (~ 198 K) is the black dashed line.
