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

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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.

At a glance


  1. Detailed characterization of Shackleton crater.
    Figure 1: Detailed characterization of Shackleton crater.

    a, Topography in km; b, percentage of time illuminated; c, 10-m baseline slopes in degrees; d, surface roughness shown as RMS residual in m; e, locations of crater counts used to determine relative ages; and f, zero-phase, 1,064-nm reflectance shown as I/F. Topography, slopes and roughness are based on a 10-m spatial resolution grid of all available LOLA profiles. In ad and f, x and y axes indicate spatial scale, where (0, 0) is the lunar south pole and colour scales show magnitude of plotted quantity. White regions in b correspond to zero illumination. Panel e shows locations of craters counted to estimate relative age, plotted over 10-m slopes (colour coded as in inset). Crater regions in e correspond to: A, flat region of crater floor; A/B, entire crater floor; C, crater wall; D, crater rim crest; E/F, inner rim annulus (~5.5km); E, inner rim annulus excluding steep region (F); F, steep rim region within annulus; G, crater wall section; I, Shackleton crater deposits north of rim in flat areas; and X, secondary crater chains and clusters (removed from analysis). In f, reflectance is expressed as a radiance factor (I/F), which is defined as the ratio of the measured radiance I to the radiance F of an ideal diffusive surface in vacuum with 100% reflectance under the same illumination. Each dot represents a 0.4×0.4km pixel median average of LOLA’s spot 3 reflectance. Contours show topography at 0.2km intervals. The grey annulus shows the 17-km diameter of the steepest portion of the walls and the 7-km diameter of the floor.

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

    Elevations are contoured at 5-m intervals with colours indicating elevation with respect to 1,737.4km. The axes indicate spatial scales.


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Author information


  1. Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA

    • Maria T. Zuber,
    • David E. Smith &
    • Erwan Mazarico
  2. Department of Geological Sciences, Brown University, Providence, Rhode Island 02912, USA

    • James W. Head,
    • Alexander R. Tye &
    • Caleb I. Fassett
  3. Solar System Exploration Division, NASA/Goddard Space Flight Center, Greenbelt, Maryland 20771, USA

    • Gregory A. Neumann
  4. Stinger Ghaffarian Technologies, Greenbelt, Maryland 20770, USA

    • Mark H. Torrence
  5. Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, California 91125, USA

    • Oded Aharonson &
    • Margaret A. Rosenburg
  6. Department of Earth and Atmospheric Sciences, Purdue University, West Lafayette, Indiana 47907, USA

    • H. Jay Melosh


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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