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Constraints on the volatile distribution within Shackleton crater at the lunar south pole


Shackleton crater is nearly coincident with the Moon’s south pole. Its interior receives almost no direct sunlight and is a perennial cold trap1,2, making Shackleton a promising candidate location in which to seek sequestered volatiles3. However, previous orbital and Earth-based radar mapping4,5,6,7,8 and orbital optical imaging9 have yielded conflicting interpretations about the existence of volatiles. Here we present observations from the Lunar Orbiter Laser Altimeter on board the Lunar Reconnaissance Orbiter, revealing Shackleton to be an ancient, unusually well-preserved simple crater whose interior walls are fresher than its floor and rim. Shackleton floor deposits are nearly the same age as the rim, suggesting that little floor deposition has occurred since the crater formed more than three billion years ago. At a wavelength of 1,064 nanometres, the floor of Shackleton is brighter than the surrounding terrain and the interiors of nearby craters, but not as bright as the interior walls. The combined observations are explicable primarily by downslope movement of regolith on the walls exposing fresher underlying material. The relatively brighter crater floor is most simply explained by decreased space weathering due to shadowing, but a one-micrometre-thick layer containing about 20 per cent surficial ice is an alternative possibility.

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Figure 1: Detailed characterization of Shackleton crater.
Figure 2: High-resolution elevation map in stereographic projection of the floor of Shackleton.

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The LOLA investigation is supported by the Lunar Reconnaissance Orbiter Mission under the auspices of NASA’s Exploration Systems Mission Directorate and Science Mission Directorate. We thank T. Perron for discussions.

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Authors and Affiliations



M.T.Z. led and participated in all aspects of the analysis and wrote the paper. J.W.H. oversaw the relative age dating analysis and participated in geologic interpretation of topography, slopes and roughness. D.E.S. led the acquisition and correction of the LOLA observations. G.A.N. led the slope and roughness analysis and contributed to the development of the topographic grid. E.M. performed refined orbit adjustments and led the analysis of illumination. A.R.T. and C.I.F. performed the crater counts used in the relative age date analysis. O.A. and M.A.R. contributed to the analysis and interpretation of slopes and roughness. H.J.M. contributed to the interpretation of the crater morphology in the context of Shackleton’s geological history and volatile sequestration.

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Correspondence to Maria T. Zuber.

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The authors declare no competing financial interests.

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Zuber, M., Head, J., Smith, D. et al. Constraints on the volatile distribution within Shackleton crater at the lunar south pole. Nature 486, 378–381 (2012).

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