IRS Observations of a ToO Oort Cloud Comet at Four Heliocentric Distances from 7-3 AU

Details IRS Observations of a ToO Oort Cloud Comet at Four Heliocentric Distances from 7-3 AU IRS Observations of a ToO Oort Cloud Comet at Four Heliocentric Distances from 7-3 AU

Sep 2004

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2004sptz.prop.3152w&link_type=abstract

Spitzer Proposal ID #3152

Physics

Scientific paper

We propose a 5.3 hr non-impact ToO Spitzer (+ IRS) mapping program to observe an Oort cloud (OC) comet over a range of heliocentric distances from 7-3 AU. Based on NEAT, LINEAR, and MPEC records over the past four years, we expect in Cycle 1 the discovery of two ToO comets at heliocentric distances greater than 5 AU that also have perihelia of less than 2.5 AU. Our goal is to obtain Spitzer (+IRS) spectral energy distributions (SEDs) of the same ToO OC comet at four epochs at heliocentric distances of roughly 7, 5, 4, and 3 AU to measure the thermal emission from the coma+nucleus during the three stages of cometary activity: (7-6 AU) distant activity primarily driven by CO sublimation from the nucleus, (6-4 AU) coma onset driven by crystallization of amorphous water ice from the nucleus subsurface layers, and (4-1 AU) vigorous activity stage driven by water ice sublimation from the nucleus. In addition to these nuclear sources, (non-nuclear) distributed sources produce molecular species in the coma and are attributed to an unknown grain component(s). By fitting Spitzer (+ IRS) SEDs with dust thermal emission models, we aim to constrain and compare the dust properties in the coma during the three stages of cometary activity. 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. Grain properties such as the grain size distribution and the crystalline silicate fraction betray early solar nebula processes such as grain growth and radial transport. The composition of OC cometary nuclei reveals the physical conditions during planet formation.

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