1. 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 cnichols@uark.edu, vchevrie@uark.edu W.M. Keck Laboratory for Space Simulation, Arkansas Center for Space and Planetary Sciences, University of Arkansas, Fayetteville, Arkansas 72701 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. 1587-1591. [2] Bibring, J.P., et al. (2007) Science 317, p. 1206-1210. [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