The appearance of comet Halley in 1985-1988 opened a new era in probing chemical abundances in the early solar nebula with the collection of in situ gas samples by the GIOTTO spacecraft. Moreover, use of state-of-the-art detectors on large ground-based telescopes produced high quality spectrophotometric data ideally suited for determining chemical abundances of the volatile component of the comet nucleus. This grant supports the investigation of the abundances of volatiles in cometary nuclei. The ultimate goal is to relate these abundances to the environment for forming comets in the primitive solar nebula. The approach is to combine efforts of an observationalist and a theorist to constrain a chemical model of a comet coma using high quality ground-based data. The model which incorporates significant chemical and photolytic coma processes will be used to derive the abundances of the parent species in the nucleus. From this research the investigators hope to derive significant constraints on chemical processes which occurred in the coldest regions of the solar nebula 4.5 billion years ago.
