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R. A. Simpson (Stanford Univ.)
During several orbits in April 1994, the Clementine spacecraft high-gain antenna was aimed toward polar regions on the Moon for radar scattering experiments. The objective (Nozette et al., Science, 274, 1495-1498, 1996) was to detect enhanced backscatter in the bistatic geometry when spacecraft, polar target, and Earth-based receiver were in near perfect alignment. Such enhancement would be evidence for deposits of clean polar ice similar to results obtained from the Galilean satellites, Mercury, and Mars. Nozette et al. claimed detection of such an enhancement. After examination of the same data, we see evidence for considerable heterogeneity in scattering properties at the lunar pole. Although it is impossible to rule out ice as a factor, we would not choose that as our first explanation for the variability. Either negative or positive radar results can be consistent with Lunar Prospector neutron spectrometer data depending on purity and distribution of H2O in the regolith.