Date of Graduation

12-2015

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Space & Planetary Sciences (PhD)

Degree Level

Graduate

Department

Graduate School

Advisor

Vincent Chevrier

Committee Member

William Oliver

Second Committee Member

Mark Arnold

Third Committee Member

Timothy Kral

Keywords

Earth sciences; Brines; Chlorine; Geochemistry; Habitability; Liquid; Mars; Salts; Stability; Thermodynamic

Abstract

The WCL (Wet Chemistry Lab) instrument on board the Mars’s Phoenix Lander has identified the soluble ionic composition of the soil at the landing site. Two important ions were detected at the landing site; perchlorates (ClO4-) with a concentration of ~ 2.4 wt% and chlorides (Cl-) with a concentration of 0.54 wt%. Between chloride and perchlorate ions three other oxidized ions exist and called chlorine ions: hypochlorite ClO - (ox. state +1), chlorite ClO2- (ox. state +3) and chlorate ClO3- (ox. state +5). These oxidized ions might be existed as intermediate species on the surface of Mars but remained undetected. In fact chlorine salts could be found on any planetary body that has been altered by water in the past as chlorides that been found on Martian meteorites. Here we studied the thermodynamic modeling of different chlorine salts using two different thermodynamic models: FREZCHEM and Geochemist’s Workbench (GWB) in attempt to understand their stability and habitability under Martian conditions. We approached our goals through using different thermodynamic pathways. The first pathway was through changing the temperature around the system; evaporation (T >0ºC using both FREZCHEM and GWB) and freezing (T< 0ºC using only FREZCHEM). We found that the ubiquitous minerals that formed through this first pathway either by evaporation or freezing are magnesium chlorate hexahydrate (Mg(ClO3)2•6H2O), potassium perchlorate (KClO4) and gypsum (CaSO4•2H2O). The second pathway was through varying the relative humidity around chloride/perchlorate binary salt mixtures; deliquescence (increase RH using GWB) and efflorescence (decrease RH using GWB). Our modeling results show that the DRH values for all mixtures were generally increased with decreasing temperature. Also, highly hydrated forms usually observed at low temperatures at all cases.

Available for download on Thursday, December 14, 2017

Share

COinS