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.