The Composition of Comets

Abstract

This paper is the result of the International Cometary Workshop, held in Toulouse, France in April 2014, where the participants came together to assess our knowledge of comets prior to the ESA Rosetta Mission. In this paper, we look at the composition of the gas and dust from the comae of comets. With the gas, we cover the various taxonomic studies that have broken comets into groups and compare what is seen at all wavelengths. We also discuss what has been learned from mass spectrometers during flybys. A few caveats for our interpretation are discussed. With dust, much of our information comes from flybys. They include in situ analyses as well as samples returned to Earth for laboratory measurements. Remote sensing IR observations and polarimetry are also discussed. For both gas and dust, we discuss what instruments the Rosetta spacecraft and Philae lander will bring to bear to improve our understanding of comet 67P/Churyumov-Gerasimenko as "ground-truth" for our previous comprehensive studies. Finally, we summarize some of the inital Rosetta Mission findings.

Color Systematics of Comets and Related Bodies

“…We find no significant difference between the mean optical colors of dust in short-period (Kuiper belt) and long-period (Oort cloud) comets. Comparable uniformity is observed in the gas phase compositions of comets, where significant abundance differences exist but are uncorrelated with the dynamical type (Cochran et al 2015). In both dust and gas, relative uniformity of the properties is consistent with radial mixing of the source materials in the protoplanetary disk, and with population of the Kuiper belt and Oort cloud from overlapping regions of this disk.…”