Radar mapping of Mercury's polar anomalies

Harmon, J. K.; Slade, M. A.; Vélez, R.; Crespo, A.; Dryer, M.; Johnson, Jessica Marie

doi:10.1038/369213a0

Cited by 146 publications

(149 citation statements)

References 9 publications

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“…The startling discovery of deposits with radar properties consistent with water ice at the poles of Mercury [Harmon et al, 1994], also associated with permanently shadowed craters, led to several radar measurements of the lunar poles in the hopes of detecting similar deposits. These results are much more equivocal than the Mercury results.…”

Section: Introductionmentioning

confidence: 99%

“…The low neutron flux is interpreted to be due to the presence of hydrogen, which moderates neutron energies efficiently. While a solar wind source for these hydrogen anomalies cannot be ruled out, water ice is a plausible carrier of this hydrogen.The startling discovery of deposits with radar properties consistent with water ice at the poles of Mercury [Harmon et al, 1994], also associated with permanently shadowed craters, led to several radar measurements of the lunar poles in the hopes of detecting similar deposits. These results are much more equivocal than the Mercury results.…”

mentioning

confidence: 99%

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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.

131

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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%

mentioning

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.

131

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“…However, radar echo data reveal a quite different topography. Echoes having enhanced same-sense polarization are observed to come only from the interiors of the permanently shaded craters near the poles of Mercury [Harmon et al, 1994]. The volatile deposits that produce these echoes must therefore be spatially confined to isolated, near-circular areas embedded within the intercrater plains.…”

Section: Discussionmentioning

confidence: 99%

The neutron signature of Mercury's volatile polar deposits

Feldman¹,

Barraclough²,

Hansen³

et al. 1997

J. Geophys. Res.

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Abstract. Neutron leakage flux spectra are simulated to explore whether the nature of volatile deposits residing within the permanently shaded craters near the poles of Mercury can be identified using state-of-the-art space neutron detection techniques deployed aboard a flyby mission to Mercury. The most sensitive method for discriminating between H20 (ice)-rich and S-rich deposits involves measurement of the flux of epithermal neutrons. We conclude that a single flyby over crater Chao Meng-Fu at an altitude of 200 km is sufficient to detect a circular deposit rich in elemental sulfur at the 2.60-statistical significance level, and that a similar deposit rich in H20 can be identified at the 7.80-level. Whereas identification of a S-rich deposit is not unique but compelling because of auxiliary physical arguments, that of an H20 deposit is unique.

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“…However, theoretical modeling and some radar and orbital remote sensing observations have revealed that water ice and other volatiles could potentially exist within permanently-shadowed regions near their poles (e.g., Harmon et al, 1994) because of these bodies' relatively low orbital inclinations. Confirmation that the radar-bright regions near Mercury's poles are water ice deposits is a major measurement objective of the MESSENGER mission, set to enter Mercury orbit in 2011.…”

Section: Is There Water In Places Where We Might Not Have Expected It?mentioning

confidence: 99%

Water on Planets

Bell

2009

Proc. IAU

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Abstract.Water is an abundant molecule in the Cosmos. It has exploitable and unique spectroscopic and physical properties and has been found to be ubiquitous in places that we would expect in the standard model of solar system formation and nebular condensation: beyond the snow line in outer solar system planets, moons, asteroids, and comets. However, water is also an important constituent of planetary bodies (dominating at least one of their surfaces) in the inner solar system, likely indicating significant mixing between inner and outer solar system reservoirs of water during planetary accretion and the early history of the solar system. Water has played a critical role in the differential evolution of the terrestrial planets Venus, Earth, and Mars, and the concept of the "habitable zone" where liquid water could be stable on an Earth-like planet provides a starting point for assessing the habitability of worlds in our solar system and beyond. Examples of potentially habitable environments outside this zone in our own solar system warn us that this concept should only be a guide, however-important exceptions will no doubt occur. Recent discoveries of past liquid water and abundant present subsurface ice on Mars, of water reservoirs in unexpected places like the poles of Mercury and the Moon and the subsurface of Enceladus, of water in circumstellar disks and in the atmospheres of extrasolar planets, and the expectation of the discovery of water on Earth-like worlds in the habitable zones around other stars make this an exciting time in the study of water on planets both in our own solar system, and beyond.

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Radar mapping of Mercury's polar anomalies

Cited by 146 publications

References 9 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

The neutron signature of Mercury's volatile polar deposits

Water on Planets

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