Date of Award
Doctor of Philosophy (PhD)
Atmospheric & Oceanic Sciences
Liquid water processes that may occur on the surface and near-subsurface of Mars have important implications for the present-day water cycle, habitability, and planetary protection policies. The presence of salts on Mars plays a role in surface-atmosphere interactions as salts enhance the soil's ability to retain water. This thesis explores the phase transitions of water upon interaction with Mars relevant salt analogs. Water uptake and loss properties of a single and complex Mars analog are examined using a Raman microscope equipped with an environmental cell. The effect of the hygroscopic salts on bacterial spores was evaluated with a focus on potential terrestrial contamination on outbound spacecraft and its influence on planetary protection concerns.
Calcium perchlorate (Ca(ClO4)2) is a highly deliquescent salt that may exist on the surface of present-day Mars. Here, we quantify the deliquescent relative humidity (DRH) and efflorescent relative humidity (ERH) of Ca(ClO4)2 as a function of temperature (223 K to 273 K) to elucidate its behavior on the surface of Mars. Mars relevant temperature and relative humidity (RH) conditions were simulated and deliquescence (solid to aqueous) and efflorescence (aqueous to solid) phase transitions of Ca(ClO4)2 were characterized. Experimental DRH values were compared to a thermodynamic model for three hydration states of Ca(ClO4)2. Calcium perchlorate was found to supersaturate, with lower ERH values than DRH values. Additionally, we conducted a 17-hour experiment to simulate a subsurface relative humidity and temperature diurnal cycle. This demonstrated that aqueous Ca(ClO4)2 solutions can persist without efflorescing for the majority of a martian sol, up to 17 hours under Mars temperature heating rates and RH conditions. Applying these experimental results to martian surface and subsurface heat and mass transfer models, we find that aqueous Ca(ClO4)2 solutions could persist for most of the martian sol under present-day conditions.
To investigate complex brine mixtures, a salt analog, deemed `Instant Mars,' was developed to closely match the individual cation and anion concentrations as reported by the Wet Chemistry Laboratory instrument at the Phoenix landing site. `Instant Mars' was developed to fully encompass and closely replicate correct concentrations of magnesium, calcium, potassium, sodium, perchlorate, chloride, and sulfate ions. Here we use two separate techniques, Raman microscopy and particle levitation, to study the water uptake and loss properties of individual Instant Mars analog particles. Raman microscope experiments reveal that Instant Mars particles can form stable, aqueous solutions at 56 +/- 5% RH at 243 K and persist as a metastable, aqueous solution down to 13 +/- 5% RH. The results presented in this thesis demonstrate that a salt analog that closely replicates in-situ measurements from the Phoenix landing site 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 RH conditions much lower than the deliquescent RH.
Finally, laboratory experiments presented here examine the interaction of B. subtilis spores (B-168) with liquid water in Mars relevant temperatures and RH conditions. In addition, Ca(ClO4)2 was mixed with the B. subtilis spores and exposed to the same diurnal cycle conditions to quantify the effects of Ca(ClO4)2 on the spores. A combination of Raman microscopy and an environmental cell allows us to visually and spectrally analyze the changes of the individual B. subtilis spores and Ca(ClO4)2 mixtures as they experience present-day martian diurnal cycle conditions. Results suggest that B-168 spores can survive the arid conditions and martian temperatures, even when exposed to Ca(ClO4)2 in the crystalline or aqueous phase. The extreme hygroscopic nature of Ca(ClO4)2 allows for direct interaction of B-168 spores with liquid water. The results impact the understanding of planetary protection and forward contamination concerns for future missions.
Nuding, Danielle L., "Water Uptake by Mars Salt Analogs: An Investigation of Stable Aqueous Solutions Using Raman Microscopy" (2014). Atmospheric & Oceanic Sciences Graduate Theses & Dissertations. 1.