Formation and persistence of brine on mars: Experimental simulations throughout the diurnal cycle at the phoenix landing site

Abstract

In the last fewyears, water ice and salts capable ofmelting this ice and producing liquid salinewater (brine) have been detected on Mars. Moreover, indirect evidence for brine has been found in multiple areas of the planet. Here, we simulate full diurnal cycles of temperature and atmospheric water vapor content at the Phoenix landing site for the first time and showexperimentally that, in spite of the lowMars-like chamber temperature, brine forms minutes after the ground temperature exceeds the eutectic temperature of salts in contact with water ice. Moreover, we show that the brine stays liquid for most of the diurnal cycle when enoughwater ice is available to compensate for evaporation. This is predicted to occur seasonally in areas of the polar region where the temperature exceeds the eutectic value and frost or snow is deposited on saline soils, or where water ice and salts coexist in the shallow subsurface. This is important because the existence of liquid water is a key requirement for habitability.