An analytic function of lunar surface temperature for exospheric modeling

Crider, D. H.; Sarantos, M.; Grava, C.; Williams, J. P.; Retherford, Kurt D.; Siegler, M. A.; Greenhagen, B. T.

doi:10.1016/j.icarus.2014.08.043

Cited by 48 publications

(43 citation statements)

References 11 publications

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“…We found that our “simulation‐fit” model of two Chamberlain distributions with different temperatures successfully predicts the density at the surface to within 12% everywhere. This compares with overestimates as high as 337% and 416% for the single Chamberlain distribution and its first‐order expansion, respectively, which both use single temperatures (from the Hurley et al, , model described in section 3.4). These deviations are most pronounced near the terminators.…”

Section: Datamentioning

confidence: 85%

Evidence for a Localized Source of the Argon in the Lunar Exosphere

et al. 2017

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We perform the first tests of various proposed explanations for observed features of the Moon's argon exosphere, including models of the following: spatially varying surface interactions; a source that reflects the lunar near‐surface potassium distribution; and temporally varying cold trap areas. Measurements from the Lunar Atmosphere and Dust Environment Explorer (LADEE) and the Lunar Atmosphere Composition Experiment (LACE) are used to test whether these models can reproduce the data. The spatially varying surface interactions hypothesized in previous work cannot reproduce the persistent argon enhancement observed over the western maria. They also fail to match the observed local time of the near‐sunrise peak in argon density, which is the same for the highland and mare regions and is well reproduced by simple surface interactions with a ubiquitous desorption energy of 28 kJ mol−1. A localized source can explain the observations, with a trade‐off between an unexpectedly localized source or an unexpectedly brief lifetime of argon atoms in the exosphere. To match the observations, a point‐like source requires source and loss rates of ∼1.9 × 1021 atoms s−1. A more diffuse source, weighted by the near‐surface potassium, requires much higher rates of ∼1.1 × 1022 atoms s−1, corresponding to a mean lifetime of just 1.4 lunar days. We do not address the mechanism for producing a localized source, but demonstrate that this appears to be the only model that can reproduce the observations. Large, seasonally varying cold traps could explain the long‐term fluctuation in the global argon density observed by LADEE, but not that by LACE.

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Section: Datamentioning

confidence: 85%

Evidence for a Localized Source of the Argon in the Lunar Exosphere

et al. 2017

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“…For these simulations, the Moon was a perfect sphere with uniform gravity, uniform distribution of regolith and without axial tilt. The surface temperature was calculated using smoothed (at boundaries between dayside and nightside) analytical expressions (Hurley et al, 2015). Finally, we have not considered any shielding effects nor plasma sheet interactions of the Earth's magnetotail (Wilson et al, 2006).…”

Section: 1029/2018gl080008mentioning

confidence: 99%

Solar Wind‐Induced Water Cycle on the Moon

Jones

Aleksandrov

Hibbitts

et al. 2018

Geophysical Research Letters

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The solar wind has been implicated as a source of water on airless bodies such as the Moon, asteroids, and possibly Mercury, yet a kinetic and mechanistic chemical model consistent with present-day observational data is still lacking. Utilizing available data sets on temperature-driven water formation and desorption from metal oxides (e.g., SiO 2 , TiO 2 , and Al 2 O 3 ) with surface hydroxyl defects (─OH) and experimental data from a lunar mare regolith Apollo sample (10084), the 2.8-μm optical signal on the Moon is modeled. Specifically, the presence and persistence of this band result from the balance of formation and loss mechanisms associated with solar wind production and thermal transformation of hydroxyls on and within the regolith. This cycle involves formation and release of molecular water via recombinative desorption of the chemically bound ─OH. Though this mechanism forms gas-phase H 2 O on the sunlit side, photodissociation and dissociative adsorption lead to rehydroxylation and very limited exospheric water over a lunation.Plain Language Summary The idea that water exists on the Moon has been around for many years, and its presence would provide a useful resource for human exploration. Lunar water is often observed by examining the 2.8-3 micron optical absorption feature seen in the reflecting sunlight. This feature is mainly associated with bound ─OH groups made from solar wind implantation and/or from molecular water dissociating upon adsorption onto the regolith. Molecular water can form when the Moon's surface reaches 50 K above room temperature. In this process, neighboring ─OH groups combine and react producing molecular water. This has been documented to occur at these relatively low temperatures for some metal oxides that are known constituents of the lunar regolith. The water will then leave following a ballistic trajectory and either molecularly adsorb or dissociate. We have modeled this process and show that the recent observations of the Moon's water may be mostly related to the presence of ─OH and only a small amount of exospheric water. This process can also happen on asteroids and Mercury or any other surface that is bombarded by the solar wind and can heat up above 350 K.

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“…Other minor contributions to the discrepancy between our t res and Hodges' include the different temperature map: we used Diviner's global temperature, while Hodges (and other workers) used an analytical formula. The use of an analytical formula mainly affects the terminators, owing to orographic effects (Hurley et al, 2015). In Fig.…”

Section: The Residence Timementioning

confidence: 99%