Laboratory investigation of perchlorate deliquescence at the surface of Mars with a Raman scattering lidar

Abstract

A sample of magnesium perchlorate hexahydrate was subjected to the water vapor pressure and temperatures found at the landing site of the Phoenix Mars mission. Laser Raman scattering was applied to detect the onset of deliquescence and provide a relative estimate of the quantity of water taken up and subsequently released by the sample. As the temperature of the sample decreased at the same rate as measured on Mars during the evening, significant uptake of water from the atmosphere was observed to occur prior to the frost point temperature being reached. As the temperature was lowered further, the relative humidity over ice increased to 100% and frost formed on the surface surrounding the perchlorate sample. Freezing of the brine film was observed at the eutectic temperature of −67°C, and thawing occurred at a temperature of −62°C.

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

“…In the polar regions, brine formation by the melting of ice in contact with salts is plausible because frost or snow are seasonally deposited on saline soils (Whiteway et al 2009;Martínez et al 2012), water ice is seasonally present in the shallow subsurface (Paige 1992;Mellon and Jakosky 1993;Schorghofer and Aharonson 2005;Cull et al 2010), and temperatures exceed the eutectic value of salts detected on Mars during a significant fraction of the sol (from minutes to hours depending on the location and time of the year) (Möhlmann 2011;Nuding et al 2014;. Moreover, numerical modeling and laboratory experiments indicate that brine formation by deliquescence in the polar region is theoretically possible because simulated diurnal cycles of RH and temperature at the ground at the PHX site are compatible with deliquescence of Ca(ClO 4 ) 2 and Mg(ClO 4 ) 2 salts (Möhlmann 2011;Nuding et al 2014;Nikolakakos and Whiteway 2015). However, other laboratory experiments indicate that deliquescence of perchlorates at the PHX site is not rapid enough to occur during the short periods of the day during which the environmental conditions are favorable for deliquescence because the kinetics of this reaction is too slow at Mars relevant values of temperature and water vapor pressure .…”

“…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.…”

Deliquescence‐induced wetting and RSL‐like darkening of a Mars analogue soil containing various perchlorate and chloride salts

“…Therefore, we agree with Fischer et al [2014] who showed that bulk deliquescence (meaning the formation of greater amounts of liquids) is a slow process, but in contrast to their work, we find that some salts like calcium perchlorate can start to deliquesce much more rapidly (<3.5 h). This is seen as the time during which atmospheric conditions at the Phoenix landing site would meet the conditions necessary for deliquescence to occur [Möhlmann, 2011].…”

“…Most of the research has been conducted by investigating phase changes of the salts with the aid of Raman spectroscopy, whereby the Raman laser beam was focused on small salt particles or thin layers [ Gough et al , , ; Fischer et al , ; Nuding et al , , ; Nikolakakos and Whiteway , ]. However, these studies do not take into consideration that the salts on Mars are probably intimately mixed with the soil.…”

Detección de salmueras en Marte mediante espectroscopia Raman

“…Other perchlorate hydrates like those of sodium or magnesium show similar spectra as calcium perchlorate (Fischer et al, 2014), but especially magnesium perchlorate tends to show fluorescence when excited by a 532 nm laser. Lower wavelengths have shown to be successful in preventing this (Nikolakakos and Whiteway, 2015).…”