Reservoirs for Comets Compositional Differences B

Authors: Michael A DiSanti Michael J Mumma

Publish Date: 2008/05/08

Volume: 138, Issue: 1-4, Pages: 127-145

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Abstract

Tracing measured compositions of comets to their origins continues to be of keen interest to cometary scientists and to dynamical modelers of Solar System formation and evolution This requires building a taxonomy of comets from both presentday dynamical reservoirs the Kuiper Belt hereafter KB sampled through observation of ecliptic comets primarily Jupiter Family comets or JFCs and the Oort cloud OC represented observationally by the longperiod comets and by Halley Family comets HFCs Because of their short orbital periods JFCs are subjected to more frequent exposure to solar radiation compared with OC comets The recent apparitions of the JFCs 9P/Tempel 1 and 73P/SchwassmannWachmann 3 permitted detailed observations of material issuing from below their surfaces—these comets added significantly to the compositional database on this dynamical class which is underrepresented in studies of cometary parent volatiles This chapter reviews the latest techniques developed for analysis of highresolution spectral observations from ∼2–5 μm and compares measured abundances of native ices among comets While no clear compositional delineation can be drawn along dynamical lines interesting comparisons can be made The subsurface composition of comet 9P as revealed by the Deep Impact ejecta was similar to the majority of OC comets studied Meanwhile 73P was depleted in all native ices except HCN similar to the disintegrated OC comet C/1999 S4 LINEAR These results suggest that 73P may have formed in the inner giant planets’ region while 9P formed farther out or alternatively that both JFCs formed farther from the Sun but with 73P forming later in time

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