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L.V. Starukhina (Astronomical Observatory of Kharkov University)
Alternative explanations are proposed for the results of three types of remote sensing experiments in which water is supposed to be found on the surfaces of atmosphereless celestial bodies: (1) the Neutron Spectrometer experiment on Lunar Prospector, (2) IR reflectance spectrometry in 3 micron range, and (3) radar experiments. The excess hydrogen detected near the lunar poles by Lunar Prospector as well as observation of absorption bands near 3 microns in low-resolution reflectance spectra of some asteroids, can be explained by chemical trapping of solar wind hydrogen and formation of OH groups in the superficial zones of the regolith particles, higher H content in polar regions being due to lower escape probability at low temperature. Estimations of the upper limit of concentration of chemically trapped H in regolith fit to the values observed by Neutron Spectrometer [1]. Calculations of the depths of the 3 micron absorption bands due to solar wind induced OH show that they can be even higher that those observed for many asteroids and attributed to water. High radar response from the permanently shadowed polar craters on Mercury and the Moon can be accounted for by decrease of the imaginary part of the dielectric constant with temperature. [1]. Feldman W. C. et al. Trans. AGU, 79(17), Spring Meet. Suppl., S190 (1998).