On the Chemical Constitution of Cometary Nuclei

Abstract

The observed properties of comets and the experiments of Anders et al. suggest that during the condensation of the outer parts of the solar system from the solar nebula — assumed to contain most of the C in the form of CO, the remaining O mostly in the form of H₂O, and the excess H as H₂ molecules — besides the most stable hydrocarbon (CH₄) also considerable quantities of heavier hydrocarbon were formed. When the surface of the nucleus is warmed up in re-approaching the sun, part of the solar quanta having sufficient energy for dissociating such molecules, exothermic reactions, for instance such leading, to the observed C₂ and C₃ molecules may be expected; an inhomogeneous and porous structure of the nucleus would explain the observed occurrence of short-lived discrete jets, in which a small fraction of the CO could be ionized. Since also N must be present in some quantity (observed mainly was CN and N₂ ⁺) the formation of more complex organic molecules must also have taken place. To which extent complex interstellar molecules can have survived the formation of the solar system is hard to say on the basis of present knowledge of the origin of the solar system.