Date of Graduation

8-2019

Document Type

Thesis

Degree Name

Master of Science in Space & Planetary Sciences (MS)

Degree Level

Graduate

Department

Graduate School

Advisor

Vincent Chevrier

Committee Member

Larry Roe

Second Committee Member

John Dixon

Third Committee Member

Mark Arnold

Fourth Committee Member

Edgard Rivera-Valentin

Keywords

adsorption, Mars, planetology, regolith, relative humidty, temperature, water

Abstract

NASA’s Phoenix mission allowed for investigations of Martian diurnal water vapor cycles through the collection of temperature, relative humidity, and electric conductivity data by the Thermal and Electric Conductivity Probe (TECP) instrument. Using this data and previous experimental data, we propose a regolith-driven adsorption-desorption regime at the Phoenix landing site, where parameters intrinsic to the regolith are controlling localized relative humidity at the surface. To constrain these parameters, we model adsorption as a function of temperature and relative humidity across various Mars-relevant materials, defined by two layer-based adsorption theories: Langmuir (monolayer) and Brunauer-Emmett-Teller or BET (multilayer). Langmuir serves as an ideal adsorption model at high temperatures and low relative humidity, but diverges from the data at low temperature and high relative humidity (Martian night). Over these same values, BET continues to model the data once saturation of a monolayer is achieved. The BET model yielded fairly constant values for variables: volumetric surface coverage and enthalpy values, θ = 0.336, corresponding to 2.96 x 10-7 kg of H2O/m2 and ΔH = 52.783 +/- 1.206 kJ/mol, respectively. This occurred independent of material type. Holding these values constant, we then modeled an ideal BET adsorption coefficient, C = 89.4. Using our ideal BET adsorption coefficient, coupled with an “ideal” (observed by Viking 1) specific surface area, SSA = 1.7 x 104 m2/kg, we conclude that the regolith at the Phoenix landing site is most likely a mixture mainly comprised of palagonitic material with properties similar to JSC Mars-1, which we bracket with a range of possible adsorption conditions. Ultimately, we explain adsorbed water content in the regolith at the Phoenix landing site and thus, adsorption, being driven by localized, diurnal variations in relative humidity.

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