Astronomy and Astrophysics – Astronomy
Scientific paper
Sep 2009
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009dps....41.2610h&link_type=abstract
American Astronomical Society, DPS meeting #41, #26.10
Astronomy and Astrophysics
Astronomy
Scientific paper
Hydrogen can be trapped in the surface of the moon through a variety of processes and from many different origins. Solar wind particles may explain a portion of the elevated hydrogen abundance at the lunar poles, and could react with the regolith to form water ions (OH-) (Starukhina and Shkuratov, 2000). A few layers of molecular water, such as from cometary impacts, could be thermodynamically stable at the poles (e.g. Cocks et al., 2002) although Eschelman and Parks (1999) predict that initially molecular water would be sufficiently mobile in the sunlit regions to eventually chemically bond to the regolith grains. Previous laboratory experiments support this premise, demonstrating that monolayer water forms OH- with Temperature-Programmed Desorption (TPD) analyses showing a monolayer (of OH-) on TiO2 is stable below 295K, two layers are stable below 195K, and more layers form water ice (Lane et al., 2009). Water ice can exist on the Moon, but only in the cold portions of permanently-shadowed craters (Watson et al.,1961, Vasavada et al., 1999). Even here, though, the water may exist as individually adsorbed molecules unable to migrate to form ice grains because the molecules are immobilized by the cold temperatures and electrostatic bonding to the regolith grains (Hibbitts et al., 2009). The spectral characteristics and observable strengths of the 3-micron fundamental (strongest) absorption feature are specific to these forms of `water’ and one or two layers on lunar regolith grains should have a detectable 3-micron feature given the regolith's effective surface area of 1m2/g (Cadenhead, 1972). The absorption band in water-ice is narrow positioned 3.1 microns, water is broad 2.9 microns, and the band associated with adsorbed water varies with physical state and temperature from 2.8 microns to 3 microns. This work is funded by the NASA LASER progam.
Dyar Darby
Hibbitts Charles A.
Orlando T.
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