Lunar and Planetary Laboratory
University of Arizona, Tucson, AZ 85721
sprague
fax 520-621-4933
Lunar
and Planetary Laboratory
University of Arizona, Tucson, AZ 85721
dhunten
R.W.H. KOZLOWSKI
Physics Department
Susquehanna University
Selinsgrove, PA 17870
ABSTRACT
Journal:Geophysical Research Letters (ISSN 0094-8276), vol. 15,
Sept. 1988, p. 1141-1144. Research supported by Whittaker Foundation.
Publication Date:09/1988
Abstract
Spectra showing the sodium D lines above the moon's bright limb
(subsolar point) were obtained at first and last quarters, May 27 and
June 7, 1988. The number density at the surface is 57 + or - 20 atoms/cu
cm and the scale height is 79 + or - 8 km, compatible with the
temperature of the surface. Comparison with the Mercurian density of
26,000 atoms/cu cm reveals an enigma. Despite the apparent general
similarity of the surfaces, the sodium densities are in a ratio of about
400. The difference may be attributed to differences in source or loss
mechanisms or to some fundamental compositional difference between the
two planets. The possibility that the source is rapid diffusion of
sodium through Mercury's crust and regolith is discussed, as well as
recent observational evidence that Mercury's regolith is of intermediate
rock type and may be more sodium-rich than the moon's.