EXPECTED EXTREME ULTRAVIOLET-SPECTRUM OF THE LUNAR-SURFACE

The moon was recently observed to be a source of very soft x-ray emission. The emission was most intense at wavelengths longer than 62 angstrom and was attributed to Thomson scattering of solar x-rays. This observation prompted us to study the emissions expected from the lunar surface in the wavelength range between 90 and 500 angstrom. Photons in this wavelength range scatter inefficiently. Instead, the solar x-rays are absorbed in the first several microns of lunar regolith. The absorbed x-rays can excite the surface elements and result in fluorescent emission. We find that much of the L- and M-shell extreme ultraviolet fluorescence, in the wavelength range between 90 and 500 angstrom, have higher peak intensities than the scattered solar spectrum. The total integrated fluorescent emission is also higher than the total scattered solar radiation. The L-shell fluorescent radiation can be an indicator of the surface abundances of Si, Al, Mg and other major lunar elements.