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

Journal name:
Nature
Volume:
486,
Pages:
378–381
Date published:
DOI:
doi:10.1038/nature11216
Received
Accepted
Published online

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

Figures

  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.

References

  1. Watson, K., Murray, B. C. & Brown, H. The behavior of volatiles on the lunar surface. J. Geophys. Res. 66, 30333045 (1961)
  2. Arnold, J. R. Ice in the lunar polar regions. J. Geophys. Res. 84, 56595668 (1979)
  3. Spudis, P. D., Plescia, J., Josset, J.-L. & Beauvivre, S. Geology of Shackleton Crater and the south pole of the Moon. Geophys. Res. Lett.. 36, L14201, http://dx.doi.org/10.1029/2008GL034468 (2008)
  4. Nozette, S. et al. The Clementine bistatic radar experiment. Science 274, 14951498 (1996)
  5. Stacy, N. J. S., Campbell, D. B. & Ford, P. G. Arecibo radar mapping of the lunar poles: a search for ice deposits. Science 276, 15271530 (1997)
  6. Campbell, D. B., Campbell, B. A., Carter, L. M., Margot, J.-L. & Stacy, N. J. S. No evidence for thick deposits of ice at the lunar south pole. Nature 443, 835837 (2006)
  7. Simpson, R. & Tyler, G. L. Reanalysis of Clementine bistatic radar data from the lunar south pole. J. Geophys. Res. 104, 38453862 (1999)
  8. Nozette, S. et al. Integration of lunar polar remote-sensing data sets: evidence for ice at the lunar south pole. J. Geophys. Res. 106 (E10). 2325323266 (2001)
  9. Haruyama, J. et al. Lack of exposed ice inside lunar south pole Shackleton crater. Science 322, 938939 (2008)
  10. Smith, D. E. et al. The Lunar Orbiter Laser Altimeter investigation on the Lunar Reconnaissance Orbiter mission. Space Sci. Rev. 150, 209241 (2010)
  11. Smith, D. E. et al. Results from the Lunar Orbiter Laser Altimeter (LOLA): global, high resolution topographic mapping of the Moon. Lunar Planet. Sci. Conf. XLII, 2350 (2011)
  12. Mazarico, E. et al. Orbit determination of the Lunar Reconnaissance Orbiter. J. Geod. 86, 193207 (2012)
  13. Sun, X. et al. The Laser Ranging Subsystem on the Lunar Reconnaissance Orbiter. Report No. GSC-15884-1 (NASA New Technology Report, Washington DC, 2009)
  14. Zuber, M. T. et al. The Lunar Reconnaissance Orbiter laser ranging investigation. Space Sci. Rev. 150, 6380 (2010)
  15. Neumann, G. A., Rowlands, D. D., Lemoine, F. G., Smith, D. E. & Zuber, M. T. Crossover analysis of MOLA altimetric data. J. Geophys. Res. 106 (E10). 2375323768 (2001)
  16. Thomson, B. J. et al. The interior of Shackleton crater as revealed by Mini-RF orbital radar. Lunar Planet. Sci. Conf. XLII, 1626 (2011)
  17. Pike, R. J. in Impact and Explosion Cratering (eds Roddy, D. J., Pepin, R. O. & MerrillR. B., ) 489509 (Pergamon, 1977)
  18. Squyres, S. W. et al. Exploration of Victoria crater by the Mars Rover Opportunity. Science 324, 10581061 (2009)
  19. Wilhelms, D. E., Howard, K. A. & Wilshire, H. G. Geologic Map of the South Side of the Moon (Map I-1162, US Geological Survey, 1979)
  20. Ward, W. R. Past orientation of the lunar spin axis. Science 189, 377379 (1975)
  21. Howard, K. A. Fresh lunar impact craters — review of variations with size. In Proc. 5th Lunar Sci. Conf. 61–69 (Pergamon, 1974)
  22. Pike, R. J. Depth/diameter relations of fresh lunar craters: revision from spacecraft data. Geophys. Res. Lett. 1, 291294 (1974)
  23. Hapke, B. Space weathering from Mercury to the asteroid belt. J. Geophys. Res. 106 (E5). 1003910073 (2001)
  24. Zimmerman, M. I. Farrell, W. M., Stubbs, T. J., Halekas, J. S. & Jackson, T. L. Solar wind access to polar craters: feedback between surface charging and plasma expansion. Geophys. Res. Lett.. 38, L19202, http://dx.doi.org/10.1029/2011GL048880 (2011)
  25. Kwok, R., Cunningham, G. F., Zwally, H. J. & Yi, D. ICESat over Arctic sea ice: Interpretation of altimetric and reflectivity profiles. J. Geophys. Res.. 111, C06006, http://dx.doi.org/10.1029/2005JC003175 (2006)
  26. Pieters, C. M. et al. Character and spatial distribution of OH/H2O on the surface of the Moon seen by M3 on Chandrayaan-1. Science 326, 568572 (2009)
  27. Gladstone, G. R. et al. Far-ultraviolet reflectance properties of the Moon’s permanently shadowed regions. J. Geophys. Res.. 117, E00H04, http://dx.doi.org/10.1029/2011JE003913 (2012)
  28. Folkner, W. M., Williams, J. G. & Boggs, D. H. The Planetary and Lunar Ephemeris DE421 (Jet Propulsion Laboratory, Pasadena, 2008)
  29. Pavlis, D. E., Poulouse, S. G. & McCarthy, J. J. GEODYN Operations Manuals (SGT, Inc., Greenbelt, 2009)
  30. Mazarico, E., Lemoine, F. G., Han, S.-C. & Smith, D. E. GLGM-3, a degree-150 lunar gravity model from the historical tracking data of NASA Moon orbiters. J. Geophys. Res.. 115, E05001, http://dx.doi.org/10.1029/2009JE003472 (2010)
  31. Williams, J. G., Boggs, D. H. & Folkner, W. M. Lunar Orbit, Physical Librations and Surface Coordinates (Jet Propulsion Laboratory, Pasadena, 2008)

Download references

Author information

Affiliations

  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

Contributions

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.

Competing financial interests

The authors declare no competing financial interests.

Corresponding author

Correspondence to:

Author details

Supplementary information

PDF files

  1. Supplementary Information (402K)

    This file contains Supplementary Text, Supplementary Table 1, Supplementary Figures 1-2 and additional references.

Additional data