Investigation of Water Interactions With Apollo Lunar Regolith Grains

1,2Brant M. Jones,1Aleksandr Aleksandrov,3M. Darby Dyar,4Charles A. Hibbitts,1,2,4Thomas M. Orlando
Journal of Geophysical Research (Planets) (in Press) Link to Article [https://doi.org/10.1029/2019JE006147]
1School of Chemistry and Biochemistry, Georgia Institute of Technology, Atlanta, GA, USA
2Center for Space Technology and Research, Georgia Institute of Technology, Atlanta, GA, USA
3Planetary Science Institute, Tucson, AZ, USA
4John Hopkins Applied Physics Laboratory, Laurel, MD, USSchool of Physics, Georgia Institute of Technology, Atlanta, GA, USA
Published by arrangement with John Wiley & Sons

Desorption activation energies of chemisorbed water on Apollo lunar Samples 14163 and 10084 were determined by temperature program desorption (TPD) experiments conducted under ultrahigh vacuum conditions. Desorption at the grain/vacuum interface and desorption/transport of water though the porous medium with readsorption were found to reproduce the experimental TPD signal. Signal from the grain/vacuum interface yielded desorption activation energies and site probability distributions. Highland sample 14163 exhibited a broad distribution of binding site energies peaking at 60 kJ mol−1, while mare sample 10084 exhibited a narrower distribution of binding site energies peaking at 65 kJ mol−1. The highland sample adsorbed approximately 30% more water than the more space weathered and mature mare sample, suggesting maturity may not be a good predictor of the degree of molecular water uptake on lunar regolith. Water desorption from the lunar surface over a typical lunar day was simulated with the measured coverage‐dependent activation energies of the mare and highland samples. The resulting desorption profile of water through a lunar temperature cycle is in general agreement with Lunar Reconnaissance Orbiter (LRO) Lyman‐α Mapping Project (LAMP) spacecraft‐based observations of trends for both highland and mare assuming ~1% submonolayer coverage and that photon stimulated desorption is neglected.

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