The Experiment

1
Summary

• The Experiment
• The experiment involves taking a 10 gram sample
  of montmorillonite (Figure 3) heating it at 100C
  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 -20C to 20C, 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

Tools

• The Andromeda Chamber
• A chamber (Figure 1) that can simulate the
  martian atmosphere with a vacuum pump, a cooling
  system, and injecting CO2

• Clay Regolith
• The clay used in my experiments is a
  montmorillonite from Panther Creek, Colorado with
  a grain size less than 63 µm

• Theory
• We are trying to find the adsorption kinetic
  constant ka and the desorption kinetic constant
  kd.
• ? is the ratio of surface area taken by water on
  the clay over the total surface area available on
  the particles of clay. Where ? is related to the
  mass by ma ? PH2O As l.1 ma is the mass of
  adsorbed water. PH2O is the partial pressure of
  water. As 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
  ?t00 we get
  1,2
• We can then use
  with the data (Figure 4) to extract the
  constants ka and kd

• 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

• References
• 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)
• Zent, A.P., Howard, D.J. Quinn, R.C, (2001). H2O
  adsorption on smectites Application to the
  diurnal variation of H2O in the Martian
  atmosphere. Journal of Geophysical Research. 106,
  14667-14674.