High Resolution Spectroscopy of the Lunar Sodium Exosphere

We conducted a highly successful engineering run to demonstrate the feasibility of high spectral resolution observations of the lunar exosphere. From the National Solar Observatory McMath-Pierce telscope, we used a dual etalon Fabry-Perot spectometer (R = 200,000) to measure the velocity and line width of the Na D2 (5889.950 A) emission line. We observe the intensity in equatorial and polar regions from 420 km to 2 lunar radii ( 3500 km) off the limb with a 3 arcmin (360 km) field of view. The observations were made in March 2009 at full moon to 3 days after full moon. Preliminary results indicate we can measure and, in fact, see velocity displacements between different locations of 0.25 km/s. The deconvolved line width is 2 km/s. Future plans include higher velocity-resolved line profile observations (R=300,00) under different lunar phases including in and out of the Earth's magnetotail and measurements at different altitudes and latitudes to explore factors that link observed morphologies and dynamics to the sources, sinks, and escape of the lunar atmosphere. These observations will help constrain atmospheric and surface-process modeling, and help quantify source and escape mechanisms.