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A Compositional Taxonomy of Comets and Other Database Results

Wednesday, April 4, 2012

Comets are widely believed to be the most pristine objects available for detailed study remaining from the epoch of Solar System formation, and can be used as probes of the protoplanetary material incorporated at that time. Variations in chemical composition can indicate either differences in primordial conditions or evolutionary effects, and the actual cause of specific differences in properties can be determined by statistical analyses of the chemical and orbital properties of a large number of objects. We are now completing a new uniform reduction and set of analyses of 35 years of narrowband photometry of the 167 comets that form the Lowell comet database. Cluster and principle component analyses reveals 6-10 compositional groupings, several of which are sub-groups of the original carbon-chain depleted class as defined by A'Hearn et al. (1995). All evidence continues to indicate that the carbon-chain depleted class is primoridal in nature and not associated with evolution. Unexpectedly, 4 comets are identified as being depleted in ammonia but not depleted in carbon-chain molecules. A number of other findings will also be discussed.

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