Adsorption Kinetics in Martian Clay David Kennington 1,2, Vincent Chevrier 1 1 W.M. Keck Laboratory for Space Simulation, Arkansas Center for Space and Planetary Sciences, University of Arkansas, Fayetteville, AR 72701; 2 Physics Department, Virginia Commonwealth University, Richmond, VA Adsorption Kinetics in Martian Clay David Kennington 1,2, Vincent Chevrier 1 1 W.M. Keck Laboratory for Space Simulation, Arkansas Center for Space and Planetary Sciences, University of Arkansas, Fayetteville, AR 72701; 2 Physics Department, Virginia Commonwealth University, Richmond, VA The Experiment  The experiment involves taking a 10 gram sample of montmorillonite (Figure 3) heating it at 100°C over night to get all the water out, then freezing it over night in a desiccator  The sample is then placed in the chamber (Figure 2) which is brought down to 7 mbar, a temperature ranging from -20°C to 20°C, and a relative humidity ranging from 10%-80%  The mass is measured over the course of four hours in order to find the adsoprtion rate of water into the clay Why?  All the exploration on mars stems from the question “Are we alone?”  To find life we need to find water  To find water we need a decent model for the water cycle on mars Components of Water Cycle  Evaporation rate of water  Evaporation rate of brine  Effects of Wind  Diffusion of water through regolith  Adsorption/Desorption of water in regolith My Project  My project consist of measuring adsoprtion rates of water in clay regolith under mars-like conditions Summary The “Andromeda Chamber”  A chamber (Figure 1) that can simulate the martian atmosphere with a vacuum pump, a cooling system, and injecting CO 2 Clay Regolith  The clay used in my experiments is a montmorillonite from Panther Creek, Colorado with a grain size less than 63 μm Tools Figure 2: Me on top of the chamber Figure 1: Diagram of Andromeda Chamber Source: Vincent Chevrier 1 References 1.Vincent Chevrier, Daniel R. Ostrowski, Derek W.G. Sears, (2007), Experimental Study of the Sublimation of Ice Through an Unconsolidated Clay Layer and Implications for the Stability of Ice on Mars and the Possible Diurnal Variations in Atmospheric Water, Icarus (Submitted) 2.Zent, A.P., Howard, D.J. Quinn, R.C, (2001). H 2 O adsorption on smectites: Application to the diurnal variation of H2O in the Martian atmosphere. Journal of Geophysical Research. 106, Acknowledgements  I would like to thank Daniel Ostrowski and Katie Bryson for instructing me on the chamber. I would also like to thank the Arkansas Center for Space and Planetary Sciences for letting me use their equipment Figure 3: Prepared clay sample Theory  We are trying to find the adsorption kinetic constant k a and the desorption kinetic constant k d.  θ is the ratio of surface area taken by water on the clay over the total surface area available on the particles of clay. Where θ is related to the mass by m a = θ P H2O A s l. 1 m a is the mass of adsorbed water. P H2O is the partial pressure of water. A s is the specific surface area of the clay. l is the thickness of the monolayer of water on the clay in angstroms.  Using 1,2 and setting θ t=0 =0 we get 1,2  We can then use with the data (Figure 4) to extract the constants k a and k d Figure 4: Mass vs Time -10°C, 7 mbar, 77% Relative Humidity