Metastable Aqueous Perchlorate Solutions At The Phoenix Landing Site: Experimental Studies Of Phase Transitions Relevant To Mars

Details Metastable Aqueous Perchlorate Solutions At The Phoenix Landing Site: Experimental Studies Of Phase Transitions Relevant To Mars Metastable Aqueous Perchlorate Solutions At The Phoenix Landing Site: Experimental Studies Of Phase Transitions Relevant To Mars

Oct 2010

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010dps....42.5103g&link_type=abstract

American Astronomical Society, DPS meeting #42, #51.03; Bulletin of the American Astronomical Society, Vol. 42, p.1070

Astronomy and Astrophysics

Astronomy

Scientific paper

Perchlorate salts, recently discovered at the Phoenix landing site, are known to readily absorb water vapor from the atmosphere and deliquesce into an aqueous solution at room temperature. Here we examine the deliquescence (transition from crystalline solid to liquid) and also efflorescence (transition from liquid to crystalline solid) of perchlorate salts at low temperatures relevant to Mars. A Raman microscope equipped with an environmental cell was used to determine the deliquescence relative humidity (DRH) and efflorescence relative humidity (ERH) of Na+ and Mg2+ perchlorate salts as a function of both temperature (-50 to 0C) and hydration state. We find that the deliquescence of anhydrous sodium perchlorate is only slightly dependent on temperature and occurs at 38(±3)% RH. The DRH of sodium perchlorate monohydrate, however, increases with decreasing temperature from 51% at 0C to 64% at -45C. The DRH of magnesium perchlorate hexahydrate, the phase most relevant to Mars, also increases with decreasing temperature from 42% at 0C to 64% at -50C. The efflorescence of salt solutions is known to occur at a lower relative humidity than deliquescence due to the kinetic inhibition of the crystallization process. We find that this hysteresis effect does occur during low temperature perchlorate phase transitions, as the ERH values of sodium and magnesium perchlorate solutions are 13(±2)% RH and 19(±3)% RH, respectively. These results indicate that perchlorate salts could exist as metastable, supersaturated, aqueous perchlorate solutions over a wide range of Martian RH and temperature conditions. We estimate the salts could be aqueous solutions for up to 16 hours per day at the Phoenix landing site.
This research was supported by a NASA MFRP and NSF-ATM grant.

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