Evidence for water ice near the lunar poles

Abstract

Abstract. Improved versions of Lunar Prospector thermal and epithermal neutron data were studied to help discriminate between potential delivery and retention mechanisms for hydrogen on the Moon. Improved spatial resolution at both poles shows that the largest concentrations of hydrogen overlay regions in permanent shade. In the north these regions consist of a heavily cratered terrain containing many small (less than -10-km diameter), isolated craters. These border circular areas of hydrogen abundance ([H]) that is only modestly enhanced above the average equatorial value but that falls within large, flatbottomed, and sunlit polar craters. Near the south pole, [HI is enhanced within several 30-km-scale craters that are in permanent shade but is only modestly enhanced within their sunlit neighbors. We show that delivery by the solar wind cannot account for these observations because the diffusivity of hydrogen at the temperatures within both sunlit and permanently shaded craters near both poles is sufficiently low that a solar wind origin cannot explain their differences. We conclude that a significant portion of the enhanced hydrogen near both poles is most likely in the form of water molecules.

Surface Composition of Vesta: Issues and Integrated Approach

“…Measurements by Lunar Prospector's neutron spectrometer revealed excess hydrogen in lunar polar areas where there are permanently shadowed regions; however, the chemical form of H could not be determined from measurements of neutrons (Feldman et al 1998(Feldman et al , 2000(Feldman et al , 2001Lawrence et al 2006;Eke et al 2009). Excess hydrogen at the poles was also detected by the Lunar Reconnaissance Orbiter (LRO) mission's Lunar Explorer Neutron Detector (LEND) (Mitrofanov et al 2010a(Mitrofanov et al , 2010b(Mitrofanov et al , 2010cLawrence et al 2010), confirming the earlier findings.…”

LCROSS (Lunar Crater Observation and Sensing Satellite) Observation Campaign: Strategies, Implementation, and Lessons Learned

“…Due to the low angle between the Moon's rotational axis and the normal to the ecliptic plane combined with the low inclination of the Earth's orbit around the Sun, and the lunar topography, permanently shadowed regions exist at both poles of the Moon and are among the coldest regions in the Solar System (Arnold 1979;Bussey et al 2003;Feldman et al 2001;Crider and Vondrak 2003;Margot et al 1999;Stacy et al 1997;Vasavada et al 1999). The temperature of the floor of the Cabeus Crater at the impact site has been measured at 45 K by the Diviner instrument aboard the Lunar Reconnaissance Orbiter (LRO) (Paige et al 2010).…”

“…The lunar poles have never been explored in situ prior to the LCROSS mission. Previous lunar orbital missions have been unable to gather meaningful data in the UV-visible portion of the spectrum because direct sunlight never reaches these shadowed regions and studies have thus been largely based on radar data (Nozette et al 1996;Margot et al 1999) and neutron spectroscopy (Feldman et al 1998(Feldman et al , 2001) which are tantalizing but inconclusive. By bringing material into sunlight, LCROSS has therefore provided an unprecedented opportunity to understand the characteristics of this heretofore unexplored permanently shadowed polar terrain.…”

“…Based on previous (Continued) mission data, the lunar poles could harbor volatiles (Crider and Vondrak 2003, Feldman et al 1998, 2001Lawrence et al 2006;Nozette et al 1996;Vasavada et al 1999). …”

Regolith properties in the south polar region of the Moon from 70-cm radar polarimetry

“…The Lunar Prospector (LP) neutron spectrometer identified enhanced hydrogen abundance near both poles, which could be attributed to 1-2% water ice within the upper meter of the regolith in permanently shadowed craters (Feldman et al, 2001). The LP data are of too coarse resolution to determine the degree of localized volatile concentration.…”