Chemical Abundances in Comets

Abstract

Photoelectric, filter photometry and spectrophotometry allow us to derive absolute abundances for a number of species in comets. Despite large differences in morphology, in gas-to-dust ratio, and in dynamical age, there appears to be remarkably little variation from comet to comet in the relative production rates of the species studied thus far. Since many species have not yet been measured in many comets and since we are dealing primarily with daughter species, the production rates could be controlled by reaction rates in the coma but this seems unlikely. If the observed production rates are controlled by abundances in the nucleus, as seems likely, they imply that comets are uniform with depth in the nucleus and that nearly all comets formed in a homogeneous region of the pre-solar nebula.