Spitzer Observations of a ToO Bright Oort Cloud Comet at Five Heliocentric Distances from 7-2 AU

Details Spitzer Observations of a ToO Bright Oort Cloud Comet at Five Heliocentric Distances from 7-2 AU Spitzer Observations of a ToO Bright Oort Cloud Comet at Five Heliocentric Distances from 7-2 AU

Jun 2005

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2005sptz.prop20105w&link_type=abstract

Spitzer Proposal ID #20105

Physics

Scientific paper

We propose to observe a bright Oort Cloud (OC) comet at five different heliocentric distances ranging from 7 to 2 AU, beginning within a year of discovery as a target of opportunity (ToO). From large to small heliocentric distances, some molecular species, e.g., CO, have significant contributions from extended (non-nuclear) sources, which are suggested to arise from an unknown grain component. We will characterize the temperatures, sizes, and mineralogies of the grains that are the potential carriers of distributed sources by chi-square fitting thermal emission models to IRS spectral energy distributions (SEDs). The activity level of a ToO bright OC comet with changing heliocentric distance will be studied by deriving dust production rates from IRS SEDs, as well as by studying coma morphology from IRAC or MIPS images. We aim to constrain and compare the dust properties in the coma during three stages of cometary activity that are sponsored by different nuclear energy sources: 1) distant activity triggered by CO sublimation (>7-5 AU), 2) coma onset fueled by the exoergic crystallization of amorphous water ice (4-6 AU), and 3) vigorous activity driven by water sublimation (<3-4AU). In doing so, we investigate the potentially crucial roles that dust grains play in warming volatile ices and in the nature of distributed coma sources, and the role gas production plays in transporting dust grains into coma. Understanding the nature of distributed sources and investigating the co-dependence of dust properties and activity are essential to translating coma abundances into nuclear abundances. Images also will yield nuclear fluxes, that when combined with our planned complementary visual and near-IR ground-based observations of the albedo by our co-investigators, will yield constraints on the size of the nucleus. The properties and compositions of cometary nuclei yield important constraints for the physical and chemical conditions in the early solar nebula during the epoch of icy planetesimal formation.

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