Experimental Methods  Solutions were prepared of 10, 15, 20, 25 wt% MgSO 4 ; and 10.9, 13.7, 17.8, and 18.0 wt% FeSO 4  Experimental conditions inside Andromeda Chamber (Figure 2):  Atmosphere temperature ranging from -5°C to 0°C  7 mbar CO 2 atmosphere  Relative Humidity (less than) 2%  Evaporation rates determined (in mm hr -1 ) from mass loss slopes Characteristics of Mg 2+ /Fe 2+ Sulfate Brines Under Martian Conditions C. Nicholson, V. Chevrier, T. Altheide W.M. Keck Laboratory for Space Simulation, Arkansas Center for Space and Planetary Sciences, University of Arkansas, Fayetteville, Arkansas Introduction MgSO 4  Specific Locals: Meridiani Planum, Valles Marineris, Margaritifer Sinus, and Terra Meridiani 1  Involved in Martian History:  Currently found on Mars in large deposits (~5% of Martian soils) 1  Suggests liquid source of water FeSO 4  Specific Locals: Meridiani Planum, Gusev Crater 3  Involved in Martian History: - Also currently found on Mars  Good comparison to Magnesium because it is also a 2+ ion and makes 7 hydrate  Evaporation rates are used to determine water stability duration Conclusions  Evaporation rates are much lower than expected => Increased liquid brine stability at lower temperatures  Due to crystallization of hydrates: i.e. MgSO 4 ·7H 2 O, …  Longer residence time of liquid water on Mars Data Results  Sulfate samples experiences mass loss when exposed to ~7 mbar of CO 2  Determined evaporation rates of MgSO 4 (Fig. 4) & FeSO 4 (Fig. 5) brine solutions at the corresponding surface sample temperature  Both demonstrate an effect of sample concentration on the resulting evaporation rates  Formation of an ice cap slows sublimation process Figure 2: Andromeda Chamber Figure 3: Relative Mass Loss versus Time of various brine samples Figure 4: Evaporation Rate versus Temperature of MgSO 4 brine samples; includes calculated evaporation lines of Water Ice, Liquid Water and 25 wt% MgSO 4 Figure 5: Evaporation Rate versus Temperature of FeSO 4 brine samples Acknowledgements Thank you Katie Bryson for her continuous input and contagious enthusiasm, and Walter Graupner for his technical support. References [1] Gendrin, Aline, et al. (2005) Science 307, p [2] Bibring, J.P., et al. (2007) Science 317, p [3] Lane, Melissa D., et al. (2004) Geophysical Research Letters 31. Figure 8: Burn’s Cliff in Meridiani Planum; large magnesium sulfate deposit in the sediment layering Figure 1: Brine deposit at West Candor Chasma; lighter colored sediment is kieserite (MgSO 4 ·1H 2 O), darker sediment is iron oxides. Figure 6: Theoretical Evaporation Rates of Crystallizing MgSO 4 & FeSO 4 hydrated phases; includes theoretical saturated FeSO 4 (18 wt%) & MgSO 4 (26 wt%) Figure 7A: FeSO 4 brine at pressure and temperature near the beginning of chamber run; Figure 7B: FeSO 4 brine after completion of chamber run, also at pressure and temperature A B Vac. Sys Coolant Insulation Hygrometer Platform Hoist Lid Cooling coils Sampling ports Thermocouples Balance Dry Ice Thermocouple 1 m