The behavior of volatiles on the lunar surface

Watson, K.; Murray, Bruce C.; Brown, Harrison

doi:10.1029/jz066i009p03033

Cited by 436 publications

(244 citation statements)

References 17 publications

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“…The lunar poles have long been theorized to harbor ice deposits in permanently shadowed regions because these regions can act to cold trap volatile compounds, including water introduced into the lunar environment [Watson et al, 1961]. This is a fascinating possibility both because such deposits would serve as a natural resource for future human lunar activity and because the plausible sources of lunar water (e.g., comets and asteroids) are of inherent interest.…”

Section: Introductionmentioning

confidence: 99%

Integration of lunar polar remote‐sensing data sets: Evidence for ice at the lunar south pole

Nozette¹,

Spudis²,

Robinson³

et al. 2001

J. Geophys. Res.

130

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Abstract. In order to investigate the feasibility of ice deposits at the lunar south pole, we have integrated all relevant lunar polar data sets. These include illumination data, Arecibo ground-based monostatic radar data, newly processed Clementine bistatic radar data, and Lunar Prospector neutron spectrometer measurements. The possibility that the lunar poles harbor ice deposits has important implications not only as a natural resource for future human lunar activity but also as a record of inner solar system volatiles (e.g., comets and asteroids) over the past billion years or more. We find that the epithermal neutron flux anomalies, measured by Lunar Prospector, are coincident with permanently shadowed regions at the lunar south pole, particularly those associated with Shackleton crater. Furthermore, these areas also correlate with the • = 0 circular polarization ratio (CPR) enhancements revealed by new processing of Clementine bistatic radar echoes, which in turn are colocated with areas of anomalous high CPR observed by Arecibo Observatory on the lower, Sun-shadowed wall of Shackleton crater. Estimates of the extent of high CPR from Arecibo Observatory and Clementine bistatic radar data independently suggest that •10 km 2 of ice may be present on the inner Earth-facing wall of Shackleton crater. None of the experiments that obtained the data presented here were ideally suited for definitively identifying ice in lunar polar regions. By assessing the relative merits of all available data, we find that it is plausible that ice does occur in cold traps at the lunar south pole and that future missions with instruments specifically designed to investigate these anomalies are worthy. IntroductionThe lunar poles have long been theorized to harbor ice deposits in permanently shadowed regions because these regions can act to cold trap volatile compounds, including water introduced into the lunar environment [Watson et al., 1961]. This is a fascinating possibility both because such deposits would serve as a natural resource for future human lunar activity and because the plausible sources of lunar water (e.g., comets and asteroids) are of inherent interest. In fact, modeling the temperatures of shadowed craters near the poles [Ingersoll et al., 1992;Salvail and Fanale, 1994; Vasavada, 1998] shows temperatures low enough to cold trap materials substantially more volatile than water ice. Studies of the transport and retention of water ice and other volatiles also support the possibility of water ice being present at the pole [Butler, 1997; Morgan and Shemansky, 1991 ]. The latter work suggested that sputtering was rapid enough to destroy slow continuous deposits of water ice, for example, from micrometeorite water, or water produced from reduction of lunar surface materials to produce water from solar wind hydrogen but that thick deposits of ice introduced by comets or large "wet" asteroids might survive by sequestering of ice by regolith overturn.•Naval Research Laboratory, Washington, D.C. No conclusive evidence of w...

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Section: Introductionmentioning

confidence: 99%

Integration of lunar polar remote‐sensing data sets: Evidence for ice at the lunar south pole

Nozette¹,

Spudis²,

Robinson³

et al. 2001

J. Geophys. Res.

130

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“…It was suggested long ago [Watson et al, 1961;Arnold, 1979] that temperatures within permanently shaded regions near the lunar poles were sufficiently low that water delivered to the Moon by meteoroids and comets would be stable to sublimation for the lifetime of the Moon. Subsequent refinements to these estimates have supported this conclusion [Butler et al, 1993;Butler, 1997;Vasavada et al, 1999].…”

Section: Introductionmentioning

confidence: 99%

Evidence for water ice near the lunar poles

Feldman¹,

Maurice²,

Lawrence³

et al. 2001

J. Geophys. Res.

327

224

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Abstract. Improved versions of Lunar Prospector thermal and epithermal neutron data were studied to help discriminate between potential delivery and retention mechanisms for hydrogen on the Moon. Improved spatial resolution at both poles shows that the largest concentrations of hydrogen overlay regions in permanent shade. In the north these regions consist of a heavily cratered terrain containing many small (less than -10-km diameter), isolated craters. These border circular areas of hydrogen abundance ([H]) that is only modestly enhanced above the average equatorial value but that falls within large, flatbottomed, and sunlit polar craters. Near the south pole, [HI is enhanced within several 30-km-scale craters that are in permanent shade but is only modestly enhanced within their sunlit neighbors. We show that delivery by the solar wind cannot account for these observations because the diffusivity of hydrogen at the temperatures within both sunlit and permanently shaded craters near both poles is sufficiently low that a solar wind origin cannot explain their differences. We conclude that a significant portion of the enhanced hydrogen near both poles is most likely in the form of water molecules.

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“…The 1.6u inclination of the Moon's rotation axis to the normal to the ecliptic plane means that there are areas near the poles, primarily the floors and lower interior walls of impact craters, that are in permanent shadow from the Sun. Several researchers 7,8 have pointed out that ice could be stable at the low temperatures (,100 K) expected in these shadowed areas, and the idea was given significant impetus by the discovery of probable ice deposits at the poles of Mercury by Earth-based radars 9,10 . The radar echoes from Mercury's poles were interpreted as reflections from water ice on the basis of their similarity to the unusual properties of radar echoes from the icy Galilean satellites of Jupiter 4 .…”

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confidence: 99%

No evidence for thick deposits of ice at the lunar south pole

Campbell

Carter

et al. 2006

Nature

177

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Shackleton crater at the Moon's south pole has been suggested as a possible site of concentrated deposits of water ice, on the basis of modelling of bi-static radar polarization properties and interpretations of earlier Earth-based radar images 1,2 . This suggestion, and parallel assumptions about other topographic cold traps, is a significant element in planning for future lunar landings. Hydrogen enhancements have been identified in the polar regions 3 , but these data do not identify the host species or its local distribution. The earlier Earth-based radar data lack the resolution and coverage for detailed studies of the relationship between radar scattering properties, cold traps in permanently shadowed areas, and local terrain features such as the walls and ejecta of small craters. Here we present new 20-m resolution, 13-cm-wavelength radar images that show no evidence for concentrated deposits of water ice in Shackleton crater or elsewhere at the south pole. The polarization properties normally associated with reflections from icy surfaces in the Solar System 4-6 were found at all the observed latitudes and are strongly correlated with the rockstrewn walls and ejecta of young craters, including the inner wall of Shackleton. There is no correlation between the polarization properties and the degree of solar illumination. If the hydrogen enhancement observed by the Lunar Prospector orbiter 3 indicates the presence of water ice, then our data are consistent with the ice being present only as disseminated grains in the lunar regolith.The possible presence of water-ice deposits in the polar areas of the Moon has been a controversial issue since the mid-1990s. The 1.6u inclination of the Moon's rotation axis to the normal to the ecliptic plane means that there are areas near the poles, primarily the floors and lower interior walls of impact craters, that are in permanent shadow from the Sun. Several researchers 7,8 have pointed out that ice could be stable at the low temperatures (,100 K) expected in these shadowed areas, and the idea was given significant impetus by the discovery of probable ice deposits at the poles of Mercury by Earth-based radars 9,10 . The radar echoes from Mercury's poles were interpreted as reflections from water ice on the basis of their similarity to the unusual properties of radar echoes from the icy Galilean satellites of Jupiter 4 . Low-temperature water-ice surfaces can exhibit a very strong opposition effect; that is, they preferentially scatter the incident energy back towards the radar. They also preferentially reflect the same sense of circular polarization that was transmitted, leading to a circular polarization ratio (CPR, the ratio of the reflected power in the same circular (SC) sense of polarization transmitted to that in the opposite (OC) sense) greater than unity. A mirror-like reflection would have a CPR of zero, and most geological surfaces have a CPR of less than unity 11 . It is thought that these properties of the radar reflection are related to the very small propag...

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The behavior of volatiles on the lunar surface

Cited by 436 publications

References 17 publications

Integration of lunar polar remote‐sensing data sets: Evidence for ice at the lunar south pole

Integration of lunar polar remote‐sensing data sets: Evidence for ice at the lunar south pole

Evidence for water ice near the lunar poles

No evidence for thick deposits of ice at the lunar south pole

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