The discovery of a long sodium tail on comet Hale-Bopp brought a growth of interest on sodium abundance in comets. A further analysis of wide field images and high resolution spectra on Hale-Bopp allowed us to make the hypothesis of the presence of two distinct sodium tails due to different sources, one located in the nuclear region and another yielded by the release of neutral atoms by the dust particles in the coma and along the dust tail. Such findings stimulated a re-analysis of the data obtained from the ICE spacecraft in the short period comet Giacobini-Zinner providing the evidence of sodium ions in the tailward direction. Moreover very recently the sodium has been found in other short period comets as P/Hartley 2 and P/Temple-Tuttle. It appears that the sodium observed in the Hale-Bopp was not a lucky event due to the exceptional size of the nucleus and its activity, but it could be an almost common characteristic of the comets.

The sodium is an interesting element even in the interstellar medium and in some circumstellar regions as neutral atom and in molecules, and it is often used as a tracer of the hydrogen column density and/or of other processes.

The sodium sources in cometary nuclei could represent a further interesting subjects to study using the data will be acquired by space missions to better understand the main physical release processes working on the nucleus and on the dust particles and the possible relation with the interstellar medium. Furthermore a comparison of the sodium abundance in the comets and in the local interstellar medium could give us useful insights on the origin of the comet.

In this work we will try to define the nature of the sodium sources that could work in a comet and if there could be a relation with the interstellar medium.