Formation and Persistence of Brine on Mars: Experimental Simulations throughout the Diurnal Cycle at the Phoenix Landing Site

Abstract

In the last few years, water ice and salts capable of melting this ice and producing liquid saline water (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 show experimentally that, in spite of the low Mars-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 enough water 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. Key Words: Mars—Ice—Perchlorates—Brine—Water—Raman spectroscopy. Astrobiology 16, 937–948.

The Effect of Mars‐Relevant Soil Analogs on the Water Uptake of Magnesium Perchlorate and Implications for the Near‐Surface of Mars

“…At the PHX landing site, though, high RH periods during the summer are accompanied by temperatures above the eutectic temperature in the subsurface and are able to potentially generate a liquid phase if magnesium perchlorate is present, even if mixed with mineral soil analogs. These findings are consistent with several other studies on the presence of liquid at the PHX landing site (Cull et al, ; Fischer et al, , ; Zorzano et al, ).…”

“…Many recent studies have examined the deliquescence, efflorescence, or freezing of pure perchlorate salts or brines (Fischer et al, , ; Gough et al, ; Nikolakakos & Whiteway, ; Nuding et al, ; Primm et al, ; Toner et al, ). The low‐temperature phase transition behavior of many pure perchlorates is therefore fairly well established.…”

Laboratory study of adsorption and deliquescence on the surface of Mars

“…Confidential manuscript submitted to JGR-Planets tations of liquids at the Phoenix landing site have further been supported by experimental results that suggest a role for deliquescence [Chevrier et al, 2009;Nuding et al, 2014;Fischer et al, 2016].…”

Water uptake and hygroscopicity of perchlorates and implications for the existence of liquid water in some hyperarid environments

“…[21][22][23][24][25] Several laboratory and theoretical studies have investigated the deliquescence and efflorescence of perchlorates at different temperatures. 22,23,[25][26][27][28] For example, a laboratory study by Zorzano et al 23 found that sodium perchlorate could absorb water vapor and form aqueous solutions under Martian conditions at temperatures as low as 225 K. The deliquescence relative humidity (DRH) decreases from 64% at 223 K to 42% at 273 K for Mg(ClO 4 ) 2 $6H 2 O, and decreases from 64% at 228 K to 51% at 273 K for NaClO 4 $H 2 O. 25 The DRH of calcium perchlorate varies between 5% and 55% for the temperature range of 223-273 K, 22 probably because the hydration state of calcium perchlorate changes at different temperatures.…”