^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.

¹G. M. Wong,^2,3,4J. M. T. Lewis,^3,4C. A. Knudson,^4,5M. Millan,³A. C. McAdam,³J. L. Eigenbrode,³S. Andrejkovičová,⁶F. Gómez,⁷R. Navarro‐González,¹C. H. House
Journal of Geophysical Research (Planets) (in Press) Link to Article [https://doi.org/10.1029/2019JE006304]
¹Department of Geosciences, Pennsylvania State University, University Park, PA
²Department of Physics and Astronomy, Howard University, Washington, D.C.
³Planetary Environments Laboratory, NASA Goddard Space Flight Center, Greenbelt, MD
⁴Center for Research and Exploration in Space Science and Technology, NASA GSFC, Greenbelt, MD
⁵Department of Biology, Georgetown University, Washington, DC
⁶Centro de Astrobiologia (CSIC‐INTA), Torrejón de Ardoz, Madrid, Spain
⁷Instituto de Ciencias Nucleares, Universidad Nacional Autónoma de México, Ciudad Universitaria, Ciudad de México, Mexico
Published by arrangement with John Wiley & Sons

The Mars Science Laboratory mission investigated Vera Rubin ridge, which bears spectral indications of elevated amounts of hematite and has been hypothesized as having a complex diagenetic history. Martian samples, including three drilled samples from the ridge, were analyzed by the Sample Analysis at Mars instrument suite via evolved gas analysis‐mass spectrometry (EGA‐MS). Here, we report new EGA‐MS data from Martian samples and describe laboratory analogue experiments. Analyses of laboratory analogues help determine the presence of reduced sulfur in Martian solid samples, which could have supported potential microbial life. We used evolved carbonyl sulfide (COS) and carbon disulfide (CS₂) to identify Martian samples likely to contain reduced sulfur by applying a quadratic discriminant analysis. While we report results for 24 Martian samples, we focus on Vera Rubin ridge samples and select others for comparison. Our results suggest the presence of reduced sulfur in the Jura member of Vera Rubin ridge, which can support various diagenetic history models, including, as discussed in this work, diagenetic alteration initiated by a mildly reducing, sulfite‐containing groundwater.