Fluxes of Fast and Epithermal Neutrons from Lunar Prospector Evidence for Water Ice at the Lunar Poles W C Feldman et al Science 281 1496 1998 DOI 10 1126 science 281 5382 1496 The following resources related to this article are available online at www sciencemag org this information is current as of September 1 2008 This article cites 14 articles 6 of which can be accessed for free http www sciencemag org cgi content full 281 5382 1496 otherarticles This article has been cited by 104 article s on the ISI Web of Science This article has been cited by 4 articles hosted by HighWire Press see http www sciencemag org cgi content full 281 5382 1496 otherarticles This article appears in the following subject collections Planetary Science http www sciencemag org cgi collection planet sci Information about obtaining reprints of this article or about obtaining permission to reproduce this article in whole or in part can be found at http www sciencemag org about permissions dtl Science print ISSN 0036 8075 online ISSN 1095 9203 is published weekly except the last week in December by the American Association for the Advancement of Science 1200 New York Avenue NW Washington DC 20005 Copyright 1998 by the American Association for the Advancement of Science all rights reserved The title Science is a registered trademark of AAAS Downloaded from www sciencemag org on September 1 2008 Updated information and services including high resolution figures can be found in the online version of this article at http www sciencemag org cgi content full 281 5382 1496 REPORTS References and Notes 1 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 be underrepresented in the results from analysis of spectral 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 1496 10 L A Haskin and P H Warren in Lunar Sourcebook G H Heiken D T Vaniman B M French Eds Cambridge Univ Press New York 1991 pp 367 474 figure 8 3 The inverse correlation between FeO and CaO is principally due to variations in the abundance of anorthite a Ca rich and Fe poor plagioclase At higher FeO contents where the correlation flattens the rocks are typically mare basalts which contain less anorthite but more calcic pyroxenes 11 R Lingenfelter E H Canfield V E Hampel Earth Planet 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 suggest that the CSR FeO abundances in South Pole Aitken basin may be overestimated If so then it is likely that Gd and Sm abundances are higher there than we have estimated and the basin is richer in incompatible elements than we have suggested 15 This research was partially supported by NASA through a subcontract from Lockheed Martin Corporation We thank R Reedy and D Vaniman for discussions P Spudis and another referee for helpful and thorough reviews and D Thomsen for maps of lunar surface features This work was performed under the auspices of the U S Department of Energy 13 July 1998 accepted 7 August 1998 Fluxes of Fast and Epithermal Neutrons from Lunar Prospector Evidence for Water Ice at the Lunar Poles W C Feldman S Maurice A B Binder B L Barraclough R C Elphic D J Lawrence Maps of epithermal and fast neutron fluxes measured by Lunar Prospector were used to search for deposits enriched in hydrogen at both lunar poles Depressions in epithermal fluxes were observed close to permanently shaded areas at both poles The peak depression at the North Pole is 4 6 percent below the average epithermal flux intensity at lower latitudes and that at the South Pole is 3 0 percent below the low latitude average No measurable depression in fast neutrons is seen at either pole These data are consistent with deposits of hydrogen in the form of water ice that are covered by as much as 40 centimeters of desiccated regolith within permanently shaded craters near both poles The moon is depleted in all volatile elements compared with Earth 1 However water was brought to the moon by comets and asteroids and was formed by the reduction of FeO in lunar materials by solar wind hydrogen and some juvenile water may have been released from the lunar interior over billions of years 2 3 Studies of the transport of such water over the lunar surface after its release indicate that 20 to 50 should be retained as frozen water ice within permanently shaded craters near both poles 2 6 However losses due to meteoritic bombardment 3 and erosion due to particle sputtering 7 or photodissociation by interstellar hydrogen Lyman a 8 may exceed the accretion rate preventing the development and retention of permanent ice deposits at the poles W C Feldman B L Barraclough R C Elphic D J Lawrence Los Alamos National Laboratory MS D 466 Los Alamos NM 87545 USA S Maurice Observatoire Midi Pyrenees 14 avenue Edouard Belin 31400 Toulouse France A B Binder Lunar Research Institute 1180 Sunrise Drive Gilroy CA 95020 USA To whom correspondence should be addressed Email wfeldman lanl gov The interpretation of anomalously large intensities of same sense polarized radar echoes that are localized to permanently shaded craters near the poles of Mercury 9 11 as caused by deposits of nearly pure water ice suggests that similar deposits should also exist on the moon Although a report of a possible detection of water ice on the moon with Clementine data 12 supports this suggestion it is not universally accepted 13 14 We address the question of lunar water ice using epithermal and fast neutron data measured using the Lunar Prospector LP neutron spectrometer NS Expected signature of H A unique identification of chemical species enriched in hydrogen and a characterization of their spatial distribution are possible through measurement of neutron flux spectra 15 16 The magnitude of this effect at 100 km altitude is illustrated with simulated neutron flux spectra Fig 1 The different curves give neutron lethargy L E as a function of energy E for ferroan anorthosite FAN a major type of soil or