Mediating the Controversy over Cometary PAHs and Hydrated Dust Grains Using High Signal-to-Noise 5-35 micron IRS Spectra of Five Comets

Details Mediating the Controversy over Cometary PAHs and Hydrated Dust Grains Using High Signal-to-Noise 5-35 micron IRS Spectra of Five Comets Mediating the Controversy over Cometary PAHs and Hydrated Dust Grains Using High Signal-to-Noise 5-35 micron IRS Spectra of Five Comets

Mar 2008

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008sptz.prop50335h&link_type=abstract

Spitzer Proposal ID #50335

Computer Science

Scientific paper

We propose a 15.3 hr program to study the water and dust from five solar system comets during a period of active water and dust production (heliocentric distances < 3 AU) in CY5. With high signal-to-noise ratio (SNR > 100) IRS SEDs of each comet, we will be able to constrain the grain parameters of the refractory materials and model the water lines in the 5-7 micron region. Modeling the water fundamental band in the 5-7 micron region is critical for constraining at <2% the spectral signatures of carbonates and PAHs. We will also constrain phyllosilicates and crystalline silicates using the 7-35 micron SED. Species of dust such as carbonates, phyllosilicates, and PAHs have reportedly been detected in Spitzer IRS observations of comet 9P/Tempel~1 (lisse et al. 2006), however, they have not been detected in our IRS spectra of comet C/2003 K4 (LINEAR) (Woodward et al. 2007), nor in Stardust return samples (Brownlee et al. 2006). Such aqueously altered species and PAHs could be important discriminators between the dynamical comet families ecliptic comets (ECs, short-period Jupiter Family comets) and nearly isotropic comets (NICs, long period Oort cloud comets). Constraining the relative abundance of the refractory dust grains, specifically the silicate crystalline-to-amorphous ratio and placing limits on PAHs and aqueously altered species, along with the OPR of water, allows us to place strong limits on thermal processing and radial mixing in solar nebula models. Therefore, we can test the newest dynamical models on the origin of ECs and NICs. Only Spitzer's superior sensitivity and wavelength coverage can provide the data to rigorously model the water lines and fit multiple dust spectral features of major and minor dust components.

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