  Microscopic liquid brines, especially calcium-perchlorate could emerge by
deliquescence on Mars during night time hours. Using climate model computations
and orbital humidity observations, the ideal periods and their annual plus
daily characteristics at various past, current and future landing sites were
compared. Such results provide context for future analysis and targeting the
related observations by the next missions for Mars. Based on the analysis, at
most (but not all) past missions' landing sites, microscopic brine could emerge
during night time for different durations. Analysing the conditions at ExoMars
rover's primary landing site at Oxia Planum, the best annual period was found
to be between $L_s$ 115 - 225, and in $Local\hspace{0.1cm} Time$ 2 - 5, after
midnight. In an ideal case, 4 hours of continuous liquid phase can emerge
there. Local conditions might cause values to differ from those estimated by
the model. Thermal inertia could especially make such differences (low TI
values favour fast cooling and $\textrm{H}_2\textrm{O}$ cold trapping at loose
surfaces) and the concentration of calcium-perchlorate salt in the regolith
also influences the process (it might occur preferentially at long-term exposed
surfaces without recent loose dust coverage). These factors should be taken
into account while targeting future liquid water observations on Mars.
