Characteristics of Mg 2+ /Fe 2+ Sulfate Brines Under Martian Conditions

1. 1 m Hoist Thermocouple Dry Ice Lid Balance Cooling coils Platform Sampling ports Hygrometer Thermocouples Insulation Vac. Sys Coolant • Introduction • MgSO4 • Specific Locals: Meridiani Planum, Valles Marineris, Margaritifer Sinus, and Terra Meridiani1 • Involved in Martian History: • Currently found on Mars in large deposits (~5% of Martian soils)1 • Suggests liquid source of water • FeSO4 • Specific Locals: Meridiani Planum, Gusev Crater3 • 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 Data A B Figure 7A: FeSO4 brine at pressure and temperature near the beginning of chamber run; Figure 7B: FeSO4 brine after completion of chamber run, also at pressure and temperature Figure 3: Relative Mass Loss versus Time of various brine samples Characteristics of Mg2+/Fe2+ Sulfate Brines Under Martian Conditions • Results • Sulfate samples experiences mass loss when exposed to ~7 mbar of CO2 • Determined evaporation rates of MgSO4 (Fig. 4) & FeSO4 (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 4: Evaporation Rate versus Temperature of MgSO4 brine samples; includes calculated evaporation lines of Water Ice, Liquid Water and 25 wt% MgSO4 • Conclusions • Evaporation rates are much lower than expected => Increased liquid brine stability at lower temperatures • Due to crystallization of hydrates: i.e. MgSO4·7H2O, … • Longer residence time of liquid water on Mars Figure 1: Brine deposit at West Candor Chasma; lighter colored sediment is kieserite (MgSO4·1H2O), darker sediment is iron oxides. 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 • Experimental Methods • Solutions were prepared of 10, 15, 20, 25 wt% MgSO4; and 10.9, 13.7, 17.8, and 18.0 wt% FeSO4 • Experimental conditions inside Andromeda Chamber (Figure 2): • Atmosphere temperature ranging from -5°C to 0°C • 7 mbar CO2 atmosphere • Relative Humidity (less than) 2% • Evaporation rates determined (in mm hr-1) from mass loss slopes Figure 5: Evaporation Rate versus Temperature of FeSO4 brine samples Figure 8: Burn’s Cliff in Meridiani Planum; large magnesium sulfate deposit in the sediment layering 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 6: Theoretical Evaporation Rates of Crystallizing MgSO4 & FeSO4 hydrated phases; includes theoretical saturated FeSO4 (18 wt%) & MgSO4 (26 wt%) Acknowledgements Thank you Katie Bryson for her continuous input and contagious enthusiasm, and Walter Graupner for his technical support. Figure 2: Andromeda Chamber