Possibility of microscopic liquid water formation at landing sites on Mars and their observational potential

TL;DR

This study assesses the potential for microscopic liquid water formation on Mars at various landing sites using climate models and observations, highlighting optimal conditions and factors influencing brine emergence for future exploration.

Contribution

It provides a detailed analysis of the conditions under which microscopic brines could form on Mars, guiding future observational strategies and mission planning.

Findings

Microscopic brines could emerge during night at most past landing sites.

Optimal conditions at Oxia Planum include 4 hours of liquid phase after midnight.

Thermal inertia and salt concentration significantly influence brine formation potential.

Abstract

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.