Contributions of solar wind and micrometeoroids to molecular hydrogen in the lunar exosphere

Crider, D. H.; Cook, J. C.; Retherford, Kurt D.; Greathouse, T. K.; Gladstone, G. R.; Mandt, K.; Grava, C.; Kaufmann, D. E.; Hendrix, Amanda; Feldman, P. D.; Pryor, W. R.; Stickle, A. M.; Killen, R. M.; Stern, S. A.

doi:10.1016/j.icarus.2016.04.019

Cited by 32 publications

(32 citation statements)

References 37 publications

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“…The resultant H 2 molecule has enough kinetic energy to escape the 1-2-eV surface binding energy (Starukhina, 2006). Observations of the H 2 lunar exosphere obtained with LAMP are consistent with this hypothesis (Hurley et al, 2016;Stern et al, 2013). that H atoms can find a variety of pathways to escape the surface potential, but molecular hydrogen appears to be the dominant pathway.…”

Section: Introductionmentioning

confidence: 72%

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Solar Wind Implantation Into the Lunar Regolith: Monte Carlo Simulations of H Retention in a Surface With Defects and the H₂ Exosphere

et al. 2019

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The solar wind implants protons into the top 20–30 nm 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 H2 exosphere. The model results are consistent with the interpretation of the Chandrayaan‐1 M3 observations of infrared absorption spectra by surface hydroxyls as discussed in Li and Milliken (2017, https://doi.org/10.1126/sciadv.1701471). The model reproduced the latitudinal concentration of OH by using a Gaussian energy distribution of f(U0 = 0.5 eV, UW = 0.078–0.1 eV) 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 H2 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.

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Section: Introductionmentioning

confidence: 72%

“…Previous models of the Moon's H 2 exosphere have been presented by Hodges (), Hartle and Thomas (), Crider and Vondrak (), Hurley et al (), and references therein. Hartle and Thomas () used a Monte Carlo model to predict upper limits of H 2 densities to account for degassed hydrogen from solar wind implantation.…”

Section: Resultsmentioning

confidence: 99%

Solar Wind Implantation Into the Lunar Regolith: Monte Carlo Simulations of H Retention in a Surface With Defects and the H₂ Exosphere

et al. 2019

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“…In addition to potentially delivering water over long timescales (e.g., Füri et al, 2012), high-speed meteoroid impacts can mobilize secondary ejecta dust particles, atoms, and molecules (Farrell et al, 2015;Hodges, 2002;Hurley et al, 2017Hurley et al, , 2012. Additionally, the bound ejecta will continually rain back onto the lunar surface and may bury exposed volatiles over time.…”

Section: 1029/2018je005756mentioning

confidence: 99%

“…Water is thought to be continually delivered to the Moon through geological timescales by water‐bearing comets and asteroids and produced continuously in situ by the impacts of solar wind protons of oxygen‐rich minerals exposed on the surface (Arnold, ). In addition to potentially delivering water over long timescales (e.g., Füri et al, ), high‐speed meteoroid impacts can mobilize secondary ejecta dust particles, atoms, and molecules (Farrell et al, ; Hodges, ; Hurley et al, , ). Additionally, the bound ejecta will continually rain back onto the lunar surface and may bury exposed volatiles over time.…”

Section: Introductionmentioning

confidence: 99%

Impact Ejecta and Gardening in the Lunar Polar Regions

et al. 2019

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The Moon is continually bombarded by interplanetary meteoroids. While many of the meteoroid sources are near the ecliptic plane, a significant population of high‐inclination meteoroids exists at 1 au that bombards the lunar polar regions. Building on previous measurements of the response of the lunar impact ejecta cloud to known meteoroid sources, we develop an ejecta model for the entire lunar surface by incorporating the high‐inclination sources. We find that the polar regions of the Moon experience similar quantities of impact ejecta production as the equator. Due to the enhanced impactor fluxes near the equator and at high latitudes on the dawn side, lunar regolith is preferentially distributed to the mid to high‐latitude regions over long timescales, providing a pathway to mix regolith from different regions. We find impact ejecta yields at the Moon to be significantly lower than the Galilean moons, suggesting meteoroids deliver more energy to the local regolith and can be an important driver in the evolution of volatiles near the lunar surface. Additionally, we find that a polar orbiting spacecraft equipped with a dust analyzer can measure appreciable quantities of lunar ejecta near the poles to constrain the water content in the polar regions.

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“…[] and Hurley et al . [] from the lunar surface. (2) At least 20% or more of the incoming solar wind incident at the lunar surface appears to be reemitted directly as neutral H outgassing—although a fraction of this outflow appears to be highly energized [ Wieser et al ., ; McComas et al ., ] to values approaching the initial solar wind energy.…”

Section: Introductionmentioning

confidence: 99%

The statistical mechanics of solar wind hydroxylation at the Moon, within lunar magnetic anomalies, and at Phobos

et al. 2017

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We present a new formalism to describe the outgassing of hydrogen initially implanted by the solar wind protons into exposed soils on airless bodies. The formalism applies a statistical mechanics approach similar to that applied recently to molecular adsorption onto activated surfaces. The key element enabling this formalism is the recognition that the interatomic potential between the implanted H and regolith‐residing oxides is not of singular value but possess a distribution of trapped energy values at a given temperature, F(U,T). All subsequent derivations of the outward diffusion and H retention rely on the specific properties of this distribution. We find that solar wind hydrogen can be retained if there are sites in the implantation layer with activation energy values exceeding 0.5 eV. We especially examine the dependence of H retention applying characteristic energy values found previously for irradiated silica and mature lunar samples. We also apply the formalism to two cases that differ from the typical solar wind implantation at the Moon. First, we test for a case of implantation in magnetic anomaly regions where significantly lower‐energy ions of solar wind origin are expected to be incident with the surface. In magnetic anomalies, H retention is found to be reduced due to the reduced ion flux and shallower depth of implantation. Second, we also apply the model to Phobos where the surface temperature range is not as extreme as the Moon. We find the H atom retention in this second case is higher than the lunar case due to the reduced thermal extremes (that reduces outgassing).

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Contributions of solar wind and micrometeoroids to molecular hydrogen in the lunar exosphere

Cited by 32 publications

References 37 publications

Solar Wind Implantation Into the Lunar Regolith: Monte Carlo Simulations of H Retention in a Surface With Defects and the H₂ Exosphere

Solar Wind Implantation Into the Lunar Regolith: Monte Carlo Simulations of H Retention in a Surface With Defects and the H₂ Exosphere

Impact Ejecta and Gardening in the Lunar Polar Regions

The statistical mechanics of solar wind hydroxylation at the Moon, within lunar magnetic anomalies, and at Phobos

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Contributions of solar wind and micrometeoroids to molecular hydrogen in the lunar exosphere

Cited by 32 publications

References 37 publications

Solar Wind Implantation Into the Lunar Regolith: Monte Carlo Simulations of H Retention in a Surface With Defects and the H2 Exosphere

Solar Wind Implantation Into the Lunar Regolith: Monte Carlo Simulations of H Retention in a Surface With Defects and the H2 Exosphere

Impact Ejecta and Gardening in the Lunar Polar Regions

The statistical mechanics of solar wind hydroxylation at the Moon, within lunar magnetic anomalies, and at Phobos

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Product

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Solar Wind Implantation Into the Lunar Regolith: Monte Carlo Simulations of H Retention in a Surface With Defects and the H₂ Exosphere

Solar Wind Implantation Into the Lunar Regolith: Monte Carlo Simulations of H Retention in a Surface With Defects and the H₂ Exosphere