From interstellar matter to comets: Elemental abundances in interstellar dust and in comet Halley

Analogies between interstellar and cometary matter can be found in their chemical compositions, both in the gaseous and solid phases, but also in the physical processes involved like evidence for ion-molecules reactions at low temperature and for ice irradiation processes. Such analogies can be observed from 3 types of measurements: interstellar spectra, cometary observations, and analyses of interplanetary dust particles, with the help of laboratory simulation experiments. Taking into account all the present available information, a compilation of the elemental abundances in interstellar matter and in comet Halley is derived, without any assumption about the dust to gas ratio. It is found that there is a significant apparent depletion of nitrogen, presently unexplained, in both interstellar and cometary materials.