Probing Heterogeneous Efflorescence Of Mars-Relevant Salts With An Optical Levitator

The presence of liquid water on the surface and subsurface of Mars has been of interest because liquid water is essential for life as we know it. While pure liquid water is typically not stable on present-day Mars, brines of hygroscopic salts with low eutectic temperatures could be stable during certain periods of a Martian sol. Studies on these salts have focused on their homogeneous phase transitions, but the impact that Martian soil may have on the brine stability is not well established. Here, using optical levitation, we examined heterogeneous efflorescence of Mg(ClO4)(2) induced by contact with a crystal of itself, NaCl, (NH4)(2)SO4, montmorillonite, and Mojave Mars Simulant (MMS) at room temperature. NaCl and (NH4)(2)SO(4 )were chosen to analyze the effect of crystal lattice on heterogeneous efflorescence. In addition, contact efflorescence of Ca(ClO4)(2) and CaCl2 by montmorillonite was studied. The stability of all three brines was unaffected by contact with montmorillonite. An immersed heterogeneous particle can also induce efflorescence from within a droplet. The effect of immersed montmorillonite was probed for all three brines plus MgCl2, and the effect of immersed MMS was probed for Mg(ClO4)(2). The immersed particles of montmorillonite increased the efflorescence relative humidity of MgCl2 but did not affect the other brines. The inactivity of montmorillonite as a heterogeneous nucleus supports the possibility of brine stability on Mars because even salt particles in contact with or coating soil grains may sustain a brine without interference from the soil.