A MODELING INVESTIGATION OF SUDDEN SODIUM LAYERS

A time-resolved model, incorporating both vertical diffusion and chemi stry, indicates that the minimum source strength required to produce a typical sudden sodium layer (SSL) is about 3 Na atoms cm-3 s-1. Howev er, many of the mechanisms proposed to explain the formation of SSLs a re not able realistically to provide this source strength, or the sour ce strength of about 1 Na atom cm-3 s-1 that is required to maintain a n SSL over several hours. Furthermore, the sodium reservoirs do not ap pear to contain sufficient sodium to produce an SSL, although sodium i ons (Na+), and meteoric dust coated with sodium compounds, cannot be r uled out. An additional mechanism is proposed, namely, the release of atomic Na by dissociative electron attachment to sodium-containing sil icate molecules (e.g. Na2SiO3 or NaAlSiO4) that are produced by meteor ic ablation.