ORFEUS II FUV Spectrographic Observations of the Lunar Atmosphere
B. Flynn (UCB/CEA)
The lunar atmosphere was first detected by Apollo
instruments based on the surface of the Moon. These
in situ mass spectrometer measurements resulted in
detections of neutral Ar and He during lunar night with
abundances of 
cm 
. Measurements could not
be made during lunar daytime due to outgassing from
spacecraft hardware. In 1988, Earth-based observations
resulted in detections of emission from the trace species
Na and K, the first remote measurements of the lunar
atmosphere. Remote observations of Na and K have revealed
much about their atmospheric distributions, however, very
little is known of the properties of the most abundant
species, Ar and He.
In December 1996, remote FUV observations of the
lunar atmosphere were conducted using the Berkeley
Spectrograph aboard the ORFEUS-SPAS II satellite. The main
goal of the observation was to measure the distribution of
Ar above the lunar dayside for the first time, and to
search for another likely atmospheric constituent, Ne.
During the 33-minute observation, the 20''-diameter
spectrograph aperture was scanned repeatedly across the
lunar sub-solar limb to obtain data over the range
90'' from the lunar limb. Initial analysis of the
data reveals a detection of emission from Ar at 1048 Å\
and 1066 Å. A determination of the dayside Ar abundance
and analysis of the data for Ne emission will be presented.