["Tucker, O. J","Farrell, W. M","Killen, R. M","Hurley, D. M"]2019-02-01期刊论文
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The solar wind implants protons into the top 20-30nm of lunar regolith grains, and the implanted hydrogen will diffuse out of the regolith but also interact with oxygen in the regolith oxides. We apply a statistical approach to estimate the diffusion of hydrogen in the regolith hindered by forming temporary bonds with regolith oxygen atoms. A Monte Carlo simulation was used to track the temporal evolution of bound OH surface content and the H-2 exosphere. The model results are consistent with the interpretation of the Chandrayaan-1 M-3 observations of infrared absorption spectra by surface hydroxyls as discussed in Li and Milliken (2017, ). The model reproduced the latitudinal concentration of OH by using a Gaussian energy distribution of f(U-0=0.5eV, U-W=0.078-0.1eV) to characterize the activation energy barrier to the diffusion of hydrogen in space weathered regolith. In addition, the model results of the exospheric content of H-2 are consistent with observations by the Lyman Alpha Mapping Project on the Lunar Reconnaissance Orbiter. Therefore, we provide support for hydroxyl formation by chemically trapped solar wind protons. Plain Language Summary Understanding the water content in the Moon's surface and its thin atmosphere is of interest for space missions. Water products have been detected in various forms (H2O and OH) on the Moon, which are not distinguishable in the observations. Herein, we examined the contribution of OH content. The solar wind implants protons (positively charged hydrogen atoms) into the top layers of the lunar soil. The implanted H atoms spread out in the grains interacting with other atoms like oxygen. We estimate the mobility of H atoms as they travel to the surface and escape into the Moon's exosphere (very thin atmosphere). The mobility of hydrogen is hindered because they can interact with other atoms or molecules as they travel in the soil. Some hydrogen will interact with oxygen and form OH. We used a Monte Carlo (probability) simulation to track the variation in the surficial amount of OH on the Moon's surface during day and night and hydrogen released in the exosphere (very thin atmosphere). It is found that considering the effect of a variety of trapping sites (interaction sites), hydrogen mobility is needed to reproduce the content of OH in the surface and hydrogen in the exosphere.
