OBSERVATIONS OF SODIUM IN THE LUNAR ATMOSPHERE DURING INTERNATIONAL LUNAR ATMOSPHERE WEEK, 1995

by

ANN L. SPRAGU E

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 and F.A. Grosse

Susquehanna University, Selinsgrove, PA 17870



R.E. Hill and R.L. Morris

Lunar and Planetary Laboratory, The University of Arizona, Tucson, Arizona 85721



ABSTRACT

(ICARUS, 131, 372 - 381, 1998.)

We report results of a part of an organized effort of five observing gro ups to simultaneously observe sodium in the lunar atmosphere. International Lunar Atmo sphere Week spanned the week of September 15 - 22, 1995. Of the seven nights we experience d four nights with good viewing conditions. We used the Mt. Lemmon Lunar Coronagraph (MLLC) a nd DARRK spectrograph. Both are especially designed for lunar atmospheric measurem ents from the surface extending to an altitude of approximately 1 lunar radius or ~ 1700 k m (860 km geopotential height). We observed lower emission rates for Na than have been p reviously reported for relatively large phase angles (96 to 129 degrees) with the average total of D2 and D1 emission rate ~ 1 kRayleigh. A thermal component was observed only on the nigh t of Sept. 17. We observed a factor of ~2 greater column abundances over the north pole than o ver the sunlit equatorial limb on Sept. 18 while on Sept. 19, the equatorial bright limb column abundance was a factor of ~ 5 higher than the north polar. Apparent geopotential scale height s varied from 279 to 435 km, indicating an extended atmosphere. If the scale heights are represented by a temperature, values are 985 to 1470 K. The data set appears to indicate that the dominant so urce during this period was meteoritic impact volatilization.



Fig. 3. A fully processed spectral image showing the Na emission lines extendin g from the lunar surface to 1800 km in altitude (~900 km geopotential height) above the limb. Brightness close to the surface is ~4400 R for D2 and 2900 R for D1. Data are from Sept. 20, 19 95. During this observing period the emission was indicative of an extended atmosphere of relati vely low Na abundance (see Table 4 for more information).