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Characterizing the Carbonaceous Dust in the Coma of Comet C/2017 K2 (PanSTARRS) with JWST

Presentation #400.08 in the session Comets: Coma (Oral Presentation)

Published onOct 23, 2023
Characterizing the Carbonaceous Dust in the Coma of Comet C/2017 K2 (PanSTARRS) with JWST

The dust particles in cometary comae are amongst the least altered constituents of small bodies in our solar system. IR spectroscopy has long revealed the near-IR emission is dominated by cometary dust particles that are hotter than the silicates, which produce resonant emissions at ≳7.5µm. Thermal models fitted to IR spectral energy distributions of cometary comae utilize the optical constants of amorphous carbon to successfully model this hotter dust component. Amorphous carbon is identified in a few cometary anhydrous chondritic IDPs through Carbon X-ray Absorption Near Edge Spectroscopy (C-XANES) (Wirick et al. 2009). C-XANES identifies C=C bonds but IR absorption features from these bonds are not observed in the 5-8 µm region, except in a few IDPs after acid dissolution of the silicates (Matrajt et al. 2005). In contrast, laboratory absorption spectra of IDPs and Stardust organic particles reveal a 3.4 µm absorption feature attributed to aliphatic bonds in the carbonaceous matter (Matrajt et al. 2013). Rosetta’s mass spectrometer COSIMA found the dust in comet 67P/C-G to have 45 wt% (IOM-like) organic matter (Bardyn et al. 2017). Amorphous carbon, which has optical constants that are taken as proxy of the dark organic matter, has a mean mass fraction of 55% for a population of comet models fitted to Spitzer IRS 7-33 µm spectra of 22 comets (Harker et al. 2023, PSJ, submitted). The Mystery is: How does this abundant dark organic matter reveal itself in the comae of comets, given the superb sensitivity of JWST? JWST observed comet C/2017 K2 (PanSTARRS) through GO 01566 (Woodward PI) using NIRSpec IFU (2.9–5.3 μm, λ/Δλ~1000) and MIRI IFU (4.9–28.1 μm, λ/Δλ~3000) near a per-perihelion heliocentric distance of 2.03 au. We discuss the potential carriers of emission features in comet C/2017 K2 (PanSTARRS), including PAHs, super-hydrogenated PAHs, and hydrogenated amorphous carbon.

This work is based in part on observations made with the NASA/ESA/CSA James Webb Space Telescope. The data were obtained from the Mikulski Archive for Space Telescopes at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-03127 for JWST. These observations are associated with program #1566. Support for program #1566 was provided by NASA through a grant from the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-03127.

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