The contemporary model of cometary nucleus and the prospects of its improvement by space research

Abstract

No cometary nucleus has ever been observed directly. A model is deduced from ground-based and space data on cometary atmospheres. The main features of the chemical composition of cometary nuclei and the estimation of their sizes are described. The treatment of the process of vaporization of dusty ice shows, contrary to widespread opinion, that the islands on the non-volatile porous mantle are formed, not in perihelion but at large heliocentric distances and on the coldest parts of a nucleus. It is shown that the mantle does not disappear when the comet approaches the Sun, as it is often supposed, but is fluidized. The proposed model can give a number of properties of cometary nuclei but some of them can be established by direct space methods only. Such properties are the masses, the rotational velocities, the homogeneity of the dust-ice mixture, the internal structure, the power of the internal sources of energy.