Lunar soil hydration constrained by exospheric water liberated by meteoroid impacts

Benna, M.; Hurley, D. M.; Stubbs, T. J.; Mahaffy, P. R.; Elphic, R. C.

doi:10.1038/s41561-019-0345-3

Cited by 93 publications

(92 citation statements)

References 38 publications

Supporting

Mentioning

Contrasting

Unclassified

Order By: Relevance

“…Recent Earth-based telescopic observations of lunar surface water (18) revealed fascinating latitude and time-of-day systematics consistent with measurements by Cassini (16) and Deep Impact (17). The neutral mass spectrometer on board the Lunar Atmosphere and Dust Environment Explorer spacecraft has detected sporadic water signal in the exosphere of the Moon (19)(20)(21)(22) with occurrence rate coinciding with periods of major annual meteoroid events (23).…”

mentioning

confidence: 67%

Untangling the formation and liberation of water in the lunar regolith

Crandall

Gillis-Davis

Ishii

et al. 2019

Proc. Natl. Acad. Sci. U.S.A.

View full text Add to dashboard Cite

The source of water (H 2 O) and hydroxyl radicals (OH), identified on the lunar surface, represents a fundamental, unsolved puzzle. The interaction of solar-wind protons with silicates and oxides has been proposed as a key mechanism, but laboratory experiments yield conflicting results that suggest that proton implantation alone is insufficient to generate and liberate water. Here, we demonstrate in laboratory simulation experiments combined with imaging studies that water can be efficiently generated and released through rapid energetic heating like micrometeorite impacts into anhydrous silicates implanted with solar-wind protons. These synergistic effects of solar-wind protons and micrometeorites liberate water at mineral temperatures from 10 to 300 K via vesicles, thus providing evidence of a key mechanism to synthesize water in silicates and advancing our understanding on the origin of water as detected on the Moon and other airless bodies in our solar system such as Mercury and asteroids. solar wind | water | Moon

show abstract

mentioning

confidence: 67%

Untangling the formation and liberation of water in the lunar regolith

Crandall

Gillis-Davis

Ishii

et al. 2019

Proc. Natl. Acad. Sci. U.S.A.

View full text Add to dashboard Cite

show abstract

“…At Reiner Gamma, the field strength is comparable to Gerasimovich, yet Reiner Gamma shows a weaker difference in water supression. We attribute this weaker difference due to the slightly lower latitude of Reiner Gamma (7°N vs 22°S), where warmer temperatures will reduce the background water (Benna et al, ; Farrell et al, ; Hendrix et al, ; Jones et al, ; Li & Milliken, ; Tucker et al, ; Wöhler, Grumpe, Berezhnoy, & Shevchenko, ).…”

Section: Discussionmentioning

confidence: 95%

“…Furthermore, recent studies suggest that the amount of water degassed from the lunar interior may be sufficient to account for the water observed on the lunar surface (Needham & Kring, ). The possibility of water liberated from the surface by exospheric dust impacts (Benna et al, ; Hurley et al, ) also complicates assessing the origins of the lunar surface water.…”

Section: Introductionmentioning

confidence: 99%

Surface Water at Lunar Magnetic Anomalies

Garrick‐Bethell

2019

Geophysical Research Letters

View full text Add to dashboard Cite

The presence of water on the lunar surface has been confirmed by multiple Earth-based and orbital observations. However, the origins of this water and the factors that control its stability at different latitudes are still debated. Magnetic anomalies on the Moon systematically reduce solar wind flux while locally keeping other confounding variables constant, which provides a natural laboratory for understanding the contribution of solar wind to lunar surface water. We find that water mapped with Moon Mineralogy Mapper data exhibit strong suppressions at magnetic anomalies, indicating that reduced solar wind flux prevents the formation of water. Our results support the hypothesis that the solar wind contributes significantly to the presence of the lunar surface water. Future missions and studies focusing on how magnetic fields affect water production can provide essential clues about how surface water is formed on the Moon and other airless bodies. Plain Language SummaryThe presence of water and/or hydroxyl molecules on the Moon has been confirmed by multiple observations. However, the origins of the lunar surface water are still unknown. The water may arise from three possible origins: solar wind, impacts, and the lunar interior. Lunar magnetic anomalies provide a natural laboratory to assess which of the three sources may dominate. Strong magnetic fields can significantly reduce the energy and flux of solar wind particles reaching the surface while keeping other conditions unchanged, such as temperature and UV photon flux. In this study, we examined water maps derived from orbital data at magnetic anomalies across the lunar surface. We confirmed that the water content at anomalies is much lower than the surrounding regions, providing direct evidence that solar wind contributes substantially to the lunar surface water production. Future missions and studies may help quantify how magnetic fields affect the formation rate of water by solar wind implantation. These results may be important for understanding solar wind water formation on other airless bodies. Key Points:• The spatial correlation between 3-μm water absorption features from Moon Mineralogy Mapper (M 3 ) data and lunar lithospheric magnetic fields is assessed • Magnetic anomalies exhibit strong water suppressions that are not artifacts of thermal corrections • Strong suppression of water features at magnetic anomalies suggests that lunar surface water mostly originates from solar wind implantation Supporting Information:• Supporting Information S1

show abstract

“…Water present in the lunar exosphere can be chemisorbed on grain surfaces 13 . Water can be introduced by volatile-rich micrometeorites, and a portion of this water can be retained in the glasses resulting from these impacts 14 or introduced into the exosphere, available for chemisorption 15 . Water can be formed in situ on grain surfaces from pre-existing hydroxyl that undergoes recombinative desorption at high lunar noontime temperatures, particularly at the equator, also releasing this water into the exosphere for later loss or trapping 16 .…”

mentioning

confidence: 99%

“…Our results are more consistent with the existence of a mechanism that produces water by impact from pre-existing lunar material, perhaps the mechanism of Zhu et al 17 , than impact-delivered water. Analysis of data taken near the equator by the Lunar Atmosphere and Dust Environment Explorer (LADEE) suggests that smaller impacts that probe the upper few centimetres of the regolith do not result in water released to the exosphere and that the uppermost few centimetres of soils are desiccated 15 . LADEE results also show that the impacts that do result in exospheric water exsolve more water than the impactor can contain.…”

mentioning

confidence: 99%

Molecular water detected on the sunlit Moon by SOFIA

et al. 2020

Self Cite

View full text Add to dashboard Cite

Widespread hydration was detected on the lunar surface through observations of a characteristic absorption feature at 3 µm by three independent spacecraft 1-3. Whether the hydration is molecular water (H 2 O) or other hydroxyl (OH) compounds is unknown and there are no established methods to distinguish the two using the 3 µm band 4. However, a fundamental vibration of molecular water produces a spectral signature at 6 µm that is not shared by other hydroxyl compounds 5. Here, we present observations of the Moon at 6 µm using the NASA/DLR Stratospheric Observatory for Infrared Astronomy (SOFIA). Observations reveal a 6 µm emission feature at high lunar latitudes due to the presence of molecular water on the lunar surface. On the basis of the strength of the 6 µm band, we estimate abundances of about 100 to 400 µg g −1 H 2 O. We find that the distribution of water over the small latitude range is a result of local geology and is probably not a global phenomenon. Lastly, we suggest that a majority of the water we detect must be stored within glasses or in voids between grains sheltered from the harsh lunar environment, allowing the water to remain on the lunar surface. Using SOFIA and the Faint Object infraRed CAmera for the SOFIA Telescope (FORCAST) instrument, we conducted observations of the lunar surface at 6 µm on 31 August 2018 in a search for molecular water. FORCAST is well suited to look for 6 µm lunar water due to its wavelength coverage from 5 to 8 µm, spectral resolution of R = 200 and high signal-to-noise ratios. The FORCAST entrance slit that defines the portion of the Moon observed is 2.4 × 191 arcsec sampled with 248 pixels. At the lunar centre of disk the slit has a spatial extent of 4.8 × 1.5 km 2 (the spatial resolution near the limb is lower due to foreshortening). During the observations, the Moon was at a phase angle of 57.5°. We observed a region at high southern latitudes near Clavius crater and a low-latitude portion of Mare Serenitatis (Extended Data Fig. 1). Details regarding observations, site selection and data reduction can be found in the Methods. Data from SOFIA reveal a strong 6 µm emission band at Clavius crater and the surrounding terrain (Fig. 1) relative to the control location near the lunar equator, which shows low hydration in some analyses (see Methods). All spectra from the Clavius region exhibit this 6 µm emission feature. The majority of these emission peaks (98%) exceed 2σ significance relative to the background noise, and about 20% exceed 4σ significance (Extended Data Fig. 2). To determine whether the spectral properties of the lunar 6 µm band are consistent with spectra of particulate water-bearing materials, we examined other planetary materials that show a 6 µm

show abstract

Lunar soil hydration constrained by exospheric water liberated by meteoroid impacts

Cited by 93 publications

References 38 publications

Untangling the formation and liberation of water in the lunar regolith

Untangling the formation and liberation of water in the lunar regolith

Surface Water at Lunar Magnetic Anomalies

Molecular water detected on the sunlit Moon by SOFIA

Contact Info

Product

Resources

About