The aqueous stability of a Mars salt analog: Instant Mars

Abstract

Due to their stability in low-temperature conditions, aqueous salt solutions are the favored explanation for potential fluid features observed on present-day Mars. A salt analog was developed to closely match the individual cation and anion concentrations at the Phoenix landing site as reported by the Wet Chemistry Laboratory instrument. "Instant Mars" closely replicates correct relative concentrations of magnesium, calcium, potassium, sodium, perchlorate, chloride, and sulfate ions. A Raman microscope equipped with an environmental cellprobed liquid water uptake and loss by Instant Mars particles in a Mars relevant temperature and relative humidity (RH) environment. Our experiments reveal that Instant Mars particles can form stable, aqueous solutions starting at 56 ± 5% RH between 235 K and 243 K and persist as a metastable, aqueous solution at or above 13 ± 5% RH. Particle levitation using an optical trap examined the phase state and morphology of suspended Instant Mars particles exposed to changing water vapor conditions at room temperature. Levitation experiments indicate that water uptake began at 42 ± 8% RH for Instant Mars particles at 293 K. As RH is decreased at 293 K, the aqueous Instant Mars particles transition into a crystalline solid at 18 ± 7% RH. These combined results demonstrate that Instant Mars can take up water vapor from the surrounding environment and transition into a stable, aqueous solution. Furthermore, this aqueous Instant Mars solution can persist as a metastable, supersaturated solution in low-RH conditions.

The Modern Near-Surface Martian Climate: A Review of In-situ Meteorological Data from Viking to Curiosity

“…Two mechanisms have been suggested for brine formation on Mars: its formation by salts absorbing atmospheric water vapor (deliquescence) when the relative humidity exceeds a threshold value known as the deliquescence relative humidity and the temperature is above the salts' eutectic value (Clark 1978;Rennó et al 2009;Davila et al 2010;Gough et al 2011;Nuding et al 2015;Martín-Torres et al 2015;Nikolakakos and Whiteway 2015), and its formation by salts melting water ice when the temperature exceeds the eutectic value of salts in contact with water ice (Brass 1980;Clark and Van Hart 1981;Fairén et al 2009;. Perchlorate salts, in particular Ca(ClO 4 ) 2 , Mg(ClO 4 ) 2 and Na(ClO 4 ) salts, are extremely relevant for brine formation via deliquescence and melting because they have low eutectic temperatures and were found in polar and equatorial regions Glavin et al 2013), suggesting that they are distributed globally.…”

Downslope sediment transport by boiling liquid water under Mars-like conditions: experiments and potential implications for Martian gullies

“…The range of conditions allowing liquid water can be broadened if dissolved salts (brines) are considered as the presence of salts depressing the melting point and evaporation rate (Brass 1980;Sears & Chittenden 2005;Masterton & Hurley 2011;Nuding et al 2015). Although evaporation has been considered in previous studies of water flow at the Martian surface (e.g.…”

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

“…We focus on the formation of brine by the contact of either surface or subsurface water ice with Ca(ClO 4 ) 2 because this salt is likely present at the Phoenix landing site (Hecht et al , 2009; Kounaves et al , 2014) and at Gale Crater (Glavin et al , 2013), suggesting that it is ubiquitous on Mars (Kounaves et al , 2014). Furthermore, the eutectic temperature of Ca(ClO 4 ) 2 is extremely low ( T E ∼ 199 K) (Marion et al , 2010), and it changes phases at similar environmental conditions as a salt mixture closely matching the individual cation/anion concentrations found in the regolith of the Phoenix landing site on Mars' polar region (Nuding et al , 2015). Finally, we focus on Ca(ClO 4 ) 2 because liquid solutions of other perchlorate salts have already been studied in detail (Chevrier et al , 2009).…”