Neutral sodium atoms release from the surface of the Moon induced by meteoroid impacts

Abstract

In this work, we calculate the vapour and neutral Na production rates on the Moon, as due to the impacts of meteoroids in the radius range of 10 -8 -0.15 m. We limit our calculations to this size range, since meteoroids with radius larger than 0.15 m have not been found to be important for the production of the exosphere in a time interval comparable with that of the observations. We have considered a new dynamical model of the flux of meteoroids at the heliocentric distance of the Moon, regarding objects in the radius range of 10 -2 -0.15 m. Instead, the flux of smaller meteoroids (radius range 10 -8 -10 -2 m) has been calculated using the two distributions adopted by Cintala and Love & Brownlee. The results of our model are that (i) the neutral Na production rate is ∼3-4.9 x 10 4 atoms cm -2 s -1 , slightly larger than the previous estimates (∼2-3 x 10 4 atoms cm -2 s -1 ), and (ii) only about 6 per cent of neutral Na is produced by the impacts of meteoroids in the size range 10 -3 -0.15 m, whereas about 94 per cent of the Na comes from the 10 -5 -10 -3 m size range.