Neutral atmospheres of comets: A distributed source model

It is argued that the typical nuclear region of a comet, under a variety of circumstances, consists of a central icy nucleus surrounded by an extended icy halo of grains forming a supplementary source for the observed atmospheric constituents. A complete hydrodynamic description of a neutral atmosphere corresponding to such a distributed source model when the predominant 'parent-molecule' is H₂O is given, and numerical results corresponding to two different velocity distributions of the icy halo consistent with smaller and larger grains are computed. The applicability and relevance of these models are discussed.