The Clementine Bistatic Radar Experiment

Nozette, S.; Lichtenberg, Christopher L.; Spudis, P. D.; Bonner, R.; Ort, W.; Malaret, E.; Robinson, M. S.; Shoemaker, E. M.

doi:10.1126/science.274.5292.1495

Cited by 364 publications

(206 citation statements)

References 28 publications

(33 reference statements)

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“…In addition, the polar deposits of Mercury exhibit a muted CBOE, thought to be caused by admixture of silicate particles into the ice regolith [Butler et al, 1993]. As the fraction of rock fragments increases, the CBOE decreases, but both Mercury and the icy Galilean satellites show that even significant amounts of silicates cannot totally remove the CBOE effect [Nozette et al, 1996]. These relations suggest that ice deposits on the Moon could contain significant amounts of particulate contamination yet still display high-CPR values caused by CBOE.…”

Section: Discussionmentioning

confidence: 99%

“…[19] High CPR on the Moon may be caused by one or both of two principal factors (1) large degrees of wavelength-scale surface roughness [e.g., Campbell, 2002Campbell, , 2012 or (2) the presence of water ice [e.g., Nozette et al, 1996Nozette et al, , 2001]. In the case of the former, geologically fresh surfaces (such as ejecta from young craters) create high degrees of surface roughness at wavelength-scales.…”

Section: Discussionmentioning

confidence: 99%

“…Images from the Clementine global mapping mission revealed large areas of darkness near the south pole of the Moon [Shoemaker et al, 1994]. Because the spatial extent of darkness was great, the Clementine team was able to improvise an experiment using the spacecraft transmitter to actively probe the dark areas near the poles with RF waves (2273 MHz, λ = 13.2 cm), receiving the echoes on Earth through the Goldstone Deep Space Network antenna [Nozette et al, 1996]. This experiment found slightly elevated circular polarization ratio (CPR); see below and also Campbell [2002] as a function of beta (phase) angle around the dark region near the south pole.…”

Section: Introductionmentioning

confidence: 99%

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Evidence for water ice on the Moon: Results for anomalous polar craters from the LRO Mini‐RF imaging radar

et al. 2013

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[1] The Mini-RF radar instrument on the Lunar Reconnaissance Orbiter spacecraft mapped both lunar poles in two different RF wavelengths (complete mapping at 12.6 cm S-band and partial mapping at 4.2 cm X-band) in two look directions, removing much of the ambiguity of previous Earth-and spacecraft-based radar mapping of the Moon's polar regions. The poles are typical highland terrain, showing expected values of radar cross section (albedo) and circular polarization ratio (CPR). Most fresh craters display high values of CPR in and outside the crater rim; the pattern of these CPR distributions is consistent with high levels of wavelength-scale surface roughness associated with the presence of block fields, impact melt flows, and fallback breccia. A different class of polar crater exhibits high CPR only in their interiors, interiors that are both permanently dark and very cold (less than 100 K). Application of scattering models developed previously suggests that these anomalously high-CPR deposits exhibit behavior consistent with the presence of water ice. If this interpretation is correct, then both poles may contain several hundred million tons of water in the form of relatively "clean" ice, all within the upper couple of meters of the lunar surface. The existence of significant water ice deposits enables both long-term human habitation of the Moon and the creation of a permanent cislunar space transportation system based upon the harvest and use of lunar propellant.

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Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Evidence for water ice on the Moon: Results for anomalous polar craters from the LRO Mini‐RF imaging radar

et al. 2013

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“…Initially, Arecibo monostatic circular polarization ratio (CPR) radar observations in the region of the lunar south pole were interpreted to possibly indicate the presence of ice deposits on the lower Earth-facing interior wall of Shackleton crater [Stacy, 1993]. Data collected by the Clementine bistatic radar experiment [Nozette et al, 1996[Nozette et al, , 1997Lichtenberg, 2000] also revealed anomalous polarization ratios in the Shackleton region, suggesting the presence of patchy, "dirty" ice deposits. Subsequently, the same Arecibo data utilized by Stacy [1993] were reported to be inconsistent with this interpretation [Stacy et al, 1997].…”

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.

127

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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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“…water ice near the south pole of the Moon [Nozette et al, 1996], a more detailed analysis of these same data [Simpson and Tyler, 1999] yielded sufficient ambiguity to question their interpretation in terms of water ice. In fact, other experiments using Earth-based radar having better spatial resolution and viewing geometry indicate that the weak signature seen by Clementine originated in sunlit areas near the south pole [Stacy et al, 1997], and similar signatures were observed far from the pole where water ice cannot be stable.…”

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confidence: 99%

Polar hydrogen deposits on the Moon

Feldman¹,

Lawrence²,

Elphic³

et al. 2000

J. Geophys. Res.

227

174

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Abstract. Neutron and gamma-ray data measured using the Lunar Prospector spectrometers were analyzed to define the enhanced hydrogen deposits near both poles of the Moon. Combining the new low-altitude neutron data (30 _+ 15 km) with previous high-altitude (tOO +_ 20 km) neutron data and the results of several recent radar investigations sharply constrains the characteristics of each of the polar deposits. The deposits at the north appear to be in the form of many small pockets or of generally distributed hydrogen that average to a tOO ppm weight fraction enhancement over that which exists in regolith at more equatorial latitudes. Those deposits in the permanently shaded craters near the south pole are consistent with a thick ferroan anorthosite regolith containing an enhancement of 1670 +_ 890 ppm hydrogen, which, if in the form of water ice, amounts to 1.5 _+ 0.8% weight fraction of H20. Neutron data alone cannot discriminate between hydrogen implanted in lunar soil from the solar wind, hydrated minerals, or H20. These craters appear to be surrounded by regolith that either contains small pockets of enhanced hydrogen or is soil that is uniformly impregnated with hydrogen enhanced on average by about tOO ppm above that contained in soils at more equatorial latitudes.

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The Clementine Bistatic Radar Experiment

Cited by 364 publications

References 28 publications

Evidence for water ice on the Moon: Results for anomalous polar craters from the LRO Mini‐RF imaging radar

Evidence for water ice on the Moon: Results for anomalous polar craters from the LRO Mini‐RF imaging radar

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

Polar hydrogen deposits on the Moon

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