 ARES CHAMBER FOR EXPERIMENTAL SIMULATIONS OF DIURNAL WATER CYCLES ON THE MARTIAN SURFACE. H. N. Farris1, V. F. Chevrier1, R. Rosario1, and L. C. Fernandez2, 1Arkansas Center for Space and Planetary Science, University of Arkansas, 202 Old Museum Building, Fayetteville, AR 72701, hnfarris@uark.edu. 2Université Toulouse III - Paul Sabatier, Insitut de Recherche en Astrophysique et Planétologie, Toulouse, France.   Introduction:  In 2001, Mars Odyssey mapped hydrogen distribution across the Martian surface, leading scientists to discover large quantities of water ice bound as ice caps in the polar regions and buried just beneath the surface in mid to high latitudes [1].  Variability in the parameters of Mars' orbit allows for mass transport of seasonal water vapor from the equatorial regions to the poles.  The stability of this water ice on Mars is largely due to the thermal and diffusive properties of the regolith.  While diffusion can explain this process over long timescales, it is the dynamics of water vapor at short timescales (day to year), which remain unknown.  Local effects, mostly related to phase changes of water, including adsorption [2], formation of liquid [3], and interaction with hygroscopic salts through hydration, deliquescence, and dissolution [3, 4, 5] can all be attributed to this lack of clarity.  In conjunction with a model developed by Rivera-Valentin, et al. [6] to understand the effect of the thermal diurnal cycle, real-time experiments are to be conducted in a simulation chamber that can mimic Martian temperature, pressure, and atmospheric composition. These experiments will be vital in understanding how the water vapor diurnal cycle can account for the formation of liquid water at the surface as well as isolating the variables of adsorption kinetics for compounds found within the Martian regolith.  Chamber Specifications:  The chamber (Fig. 1) is approximately 3 ft tall and 2 ft wide, made of stainless steel. The lower portion is surrounded by coils for cooling and then insulated with ceramic.  The lid is raised and lowered by a motor and bolted down to the base for a vacuum seal during experiments.  Chamber Instrumentation:  Near completion, the chamber (Fig. 2-4) has an iR Photonics fiber optic cable (1 to 5µm) connected to a Nicolet 6700 FTIR Spectrometer, an array of six Vaisala hygrometers (identical to those onboard MSL Curiosity) wired to a Fuji Electric digital output, a Logitech webcam, a Dino-lite digital microscope (30 µm per pixel), five Omega thermocouples, and an LED light. All the feedthrough ports for the equipment were replaced with the proper, stainless steel flanges for low-pressure experiments.  This eliminated the air leaks present at various access points around the chamber, allowing us to reach lower pressures than with the previous system.  The chamber also has an input and output connected to a chiller which pumps a glycol mixture through the cooling coils surrounding the chamber.  Lastly, there are two feed-through ports, which accommodate a vacuum pump, to achieve a desired pressure, and gas exchange for replacing the atmosphere with N2 or CO2.   Figure 1 Exterior view of the Ares Chamber     Figure 2 Schematic of exterior of the Ares Chamber  Figure 3 Schematic of interior of the Ares Chamber and components   Figure 4 Exterior view of the Ares Chamber from opposite side, showing the FTIR Spectrometer  Methodology: A series of preliminary experiments were performed in the chamber, before the modifications were made, at ambient temperature (~24°C) and pressure (1 bar).  A sample of Martian soil simulant (varying masses and types) and a hygroscopic salt (varying masses) were mixed together and placed in the chamber along with a humidity buffer (saturated salt solution) to control the relative humidity in the chamber.  The chamber was then closed and the sample was observed using an FTIR Spectrometer (1 to 5 µm). Figure 5 shows the results of an experiment using a mixture of JSC Mars-1 (150 g.) and NaClO4 (15 g.) at 100% relative humidity (buffer consisted of pure liquid water in 4 beakers resulting in a 100% relative humidity).  Within 72 hours, the salts present in the sample had deliquesced. Deliquescence is the process by which a salt, such as a perchlorate, absorbs water from the atmosphere and transforms itself from a crystalline solid phase to a liquid phase [7].  This is evident by the increase in intensity of water absorption bands at 1.4 and 1.9 µm over time.      Figure 5 Spectra of Mars regolith simulant, JSC Mars-1 and NaClO4 (10 wt%) mixture inside chamber at ambient temperature and pressure (t = 72hr).  Future Experiments:  In order to fully understand the extent that adsorption and heat transfer plays in icy soils, we will sublimate ice below a column of regolith in sizes that correspond to observations by Phoenix (~5-15 cm) [8] and Mars Odyssey (~0.5 m).  The array of thermocouples and hygrometers will enable us to observe a gradient of temperatures and relative humidities over the height of the column.   In a second set of experiments, 1-30 wt% of soluble salts will be added to the column to isolate their effects on water formation.  Salts such as magnesium or calcium perchlorate have very low eutectic temperatures (~206 K) and pose a potentially important role in the formation of aqueous liquids at the Martian surface [3]. This process is heavily dependent on the temperature and humidity of the environment; further motivation to outfit the chamber with the necessary equipment to more closely simulate Martian temperatures and pressures.  Being able to modify these conditions could expose complex subtleties in adsorption, diffusion, and deliquescence processes.  References:  [1] Boynton, W.V. et al. (2002) Science 297. [2] Chevrier V. F. et. al (2008) Icarus, 196, 459-476. [3] Sears D. W. G. et al. (2005) GRL, 32. [4] Chevrier V. F., Altheide T. S. et. al (2008) GRL, 35. [5] Chevrier V. F. et. al (2009) GRL, 36. [6] Rivera-Valentin E. G. LPSC XLI Abstract #4020 [7] Gough et al. (2011) ESPL. [8] Mellon M. T. et. al (2004) Icarus, 169, 324-340. 
