6. From Dust to Comets

Abstract

The growth and chemical evolution of a typical interstellar dust grain are followed starting from average interstellar conditions to the dense cloud and contraction phase. Based on the theory of cometary accretion directly from cold interstellar dust it is shown that the bulk material of a primordial comet would consist mostly of an icy conglomerate of complex organic molecules and frozen radicals in which are imbedded approximately equal volumes (10% each) of small grains in two different sizes - one variety being the order of 0.05 μ and the other ~0.005 μ in size - consisting mostly of silicates