LENA — Sodium detector for a lunar mission

Abstract

Sodium atoms that resonantly scatter solar radiation are excellent tracers of physical processes occuring in the lunar exosphere and on the lunar surface. Although ground-based observations have revealed many interesting features of the lunar sodium exosphere, several basic questions concerning (i) the contribution of different source mechanisms to the total sodium flux, (ii) the quantitative description of sticking and accommodation of atoms to the surface regolith, and (iii) the velocity distribution of atoms ejected from the surface are still to be answered. The planned lunar missions will provide a good opportunity to study these problems with a sensitive optical detector. We present LENA, a narrow band photometer operating at the sodium D-line and results of Monte Carlo model of its performance. A high signal to noise ratio will allow one to detect exospheric populations of sodium originating from even minor source mechanisms.