DOI: 10.1126/science.281.5382.1496 , 1496 (1998); 281Science et al.W. C. Feldman,PolesProspector: Evidence for Water Ice at the Lunar Fluxes of Fast and Epithermal Neutrons from Lunar www.sciencemag.org (this information is current as of September 1, 2008 ):The following resources related to this article are available online at http://www.sciencemag.org/cgi/content/full/281/5382/1496version of this article at: including high-resolution figures, can be found in the onlineUpdated information and services, http://www.sciencemag.org/cgi/content/full/281/5382/1496#otherarticles, 6 of which can be accessed for free: cites 14 articlesThis article 104 article(s) on the ISI Web of Science. cited byThis article has been http://www.sciencemag.org/cgi/content/full/281/5382/1496#otherarticles 4 articles hosted by HighWire Press; see: cited byThis article has been http://www.sciencemag.org/cgi/collection/planet_sciPlanetary Science : subject collectionsThis article appears in the following http://www.sciencemag.org/about/permissions.dtl in whole or in part can be found at: this articlepermission to reproduce of this article or about obtaining reprintsInformation about obtaining registered trademark of AAAS. is aScience1998 by the American Association for the Advancement of Science; all rights reserved. The title CopyrightAmerican Association for the Advancement of Science, 1200 New York Avenue NW, Washington, DC 20005. (print ISSN 0036-8075; online ISSN 1095-9203) is published weekly, except the last week in December, by theScience on September 1, 2008 www.sciencemag.orgDownloaded fromsome regions but not as well in others.A map of the difference DSeffbetween thislinear relation and the calculated Seffpoints(Fig. 3) reflects the implied abundance of neu-tron absorbers other than Fe and Ti (Fig. 4). Thehighest values are found over the rim of theImbrium basin, including the Apennine moun-tains in the east up through the Alps, acrossto the Jura mountains in the west, downthrough the Aristarchus plateau andthrough the Fra Mauro formation to thesouth. LP gamma-ray spectrometer mapsshow that these regions also have high Thand K concentrations (13). This similarityimplies that the absorbing species are affil-iated with the incompatible elements foundin KREEP; the correlation coefficient be-tween the gamma-ray spectrometer Th data(13) and DSeffis 0.93. The values of DSeffare consistent with the range (10 3 1024to42 3 1024cm2/g) of Gd and Sm contribu-tions listed in Table 1. The K in KREEPplays only a very minor role in Seff(Table1). Therefore, we conclude that DSeffre-flects primarily the concentration of Gd andSm and, thus, is a tracer for KREEP.The estimated thermal neutron macroscopicabsorption coefficient that would be expectedon the basis of concentrations of Fe and Tiderived from CSR data, coupled with an esti-mate of Ca concentrations, is in reasonableagreement with the LP neutron spectrometerresults. Discrepancies arise in regions that havesignificant levels of KREEP, where Gd and Smare major thermal neutron absorbers. Thus, theCSR method appears to be a reliable techniquefor obtaining FeO and TiO2abundances moon-wide. The inferred KREEP-rich regions form aring around the Imbrium impact site and aredirectly related to either excavation of this low-er crustal chemistry or to volcanism that extrud-ed KREEP-rich lava on the surface. On theother hand, the much larger, deeper SouthPole–Aitken impact basin shows little KREEPenhancement (14). This result appears to con-firm the uniqueness of the Imbrium lower crust-al chemistry and suggests that the moon mayhave considerable regional compositional het-erogeneity at depth.References and Notes1. P. G. Lucey, G. J. Taylor, E. Malaret, Science 268, 1150(1995).2. P. G. Lucey, D. T. Blewett, J. R. Johnson, G. J. Taylor,B. R. Hawke, Lunar Planet Sci. XXVII, 781 (1996).3. D. T. Blewett, P. G. Lucey, B. R. Hawke, B. L. Jolliff, J.Geophys. Res. 102, 16319 (1997).4. P. G. Lucey, D. T. Blewett, B. R. Hawke, ibid. 103, 3679(1998).5. P. E. Clark and A. Basu, Proc. Lunar Planet. Sci. Conf.29, 1501 (1998). Olivine is the likeliest mineral to beunderrepresented in the results from analysis of spec-tral data.6. W. C. Feldman et al., Science, 281 1496 (1998).7. W. C. Feldman et al., ibid., p. 1489 (1998).8. D. M. Drake, W. C. Feldman, B. M. Jakosky, J. Geophys.Res. 93, 6353 (1988).9. R. C. Reedy et al., Meteorit. Planet. Sci. 33 (suppl.),A127 (1998).10. L. A. Haskin and P. H. Warren, in Lunar Sourcebook, G. H.Heiken, D. T. Vaniman, B. M. French, Eds. (CambridgeUniv. Press, New York, 1991), pp. 367–474, figure 8.3.The inverse correlation between FeO and CaO is prin-cipally due to variations in the abundance of anorthite,a Ca-rich and Fe-poor plagioclase. At higher FeO con-tents where the correlation flattens, the rocks are typ-ically mare basalts, which contain less anorthite butmore calcic pyroxenes.11. R. Lingenfelter, E. H. Canfield, V. E. Hampel, EarthPlanet. Sci. Lett. 16, 355 (1972).12. W. C. Feldman, R. C. Reedy, D. S. McKay, Geophys.Res. Lett. 18, 2157 (1991).13. D. J. Lawrence et al., Science 281, 1484 (1998).14. Note added in proof: The fast neutron data suggestthat the CSR FeO abundances in South Pole–Aitkenbasin may be overestimated. If so, then it is likelythat Gd and Sm abundances are higher there thanwe have estimated, and the basin is richer inincompatible elements than we have suggested.15. This research was partially supported by NASAthrough a subcontract from Lockheed-Martin Corpo-ration. We thank R. Reedy and D. Vaniman for dis-cussions, P. Spudis and another referee for helpfuland thorough reviews, and D. Thomsen for maps oflunar surface features. This work was performed un-der the auspices of the U.S. Department of Energy.13 July 1998; accepted 7 August 1998Fluxes of Fast and EpithermalNeutrons from LunarProspector: Evidence for WaterIce at the Lunar PolesW. C. Feldman,* S. Maurice, A. B. Binder, B. L. Barraclough,R. C. Elphic, D. J. LawrenceMaps of epithermal- and fast-neutron fluxes measured by Lunar Prospectorwere used to search for deposits enriched in hydrogen at both lunar poles.Depressions in epithermal fluxes were observed close to permanently shadedareas at both poles. The peak depression at the North Pole is 4.6 percent belowthe average epithermal flux intensity at lower latitudes, and that at the SouthPole is 3.0 percent below the low-latitude average. No measurable depressionin fast neutrons is seen at either pole.