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 {\it 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
initial Rosetta Mission findings.Comment: To appear in Space Science Review
Earth-and space-based observations provide synergistic information for space mission encounters by providing data over longer timescales, at different wavelengths and using techniques that are impossible with an in situ flyby. We report here such observations in support of the EPOXI spacecraft flyby of comet 103P/Hartley 2. The nucleus is small and dark, and exhibited a very rapidly changing rotation period. Prior to the onset of activity, the period
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.