OBSERVATIONS OF SODIUM IN THE TENUOUS LUNAR ATMOSPHERE

ANN L. TYLER (SPRAGUE)

Lunar and Planetary Laboratory
University of Arizona, Tucson, AZ 85721
sprague
fax 520-621-4933


D.M.HUNTEN

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.