Gas Sources from the Coma and Nucleus of Comet 46P/Wirtanen Observed Using ALMA

Gas-phase molecules in cometary atmospheres (comae) originate primarily from (1) outgassing by the nucleus, (2) sublimation of icy grains in the near-nucleus coma, and (3) coma (photo)chemical processes. However, the majority of cometary gases observed at radio wavelengths have yet to be mapped, so...

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Bibliographic Details
Published in:The Astrophysical journal 2023-08, Vol.953 (1), p.59
Main Authors: Cordiner, M. A., Roth, N. X., Milam, S. N., Villanueva, G. L., Bockelée-Morvan, D., Remijan, A. J., Charnley, S. B., Biver, N., Lis, D. C., Qi, C., Bonev, B. P., Crovisier, J., Boissier, J.
Format: Article
Language:English
Subjects:
Abundance
Astronomy
Astrophysics
Chemical reactions
Comet heads
Comet nuclei
Comet volatiles
Cometary atmospheres
Comets
High resolution spectroscopy
Interstellar molecules
Millimeter-wave spectroscopy
Molecular spectroscopy
Outgassing
Radiative transfer
Radio interferometry
Radio telescopes
Radio waves
Sciences of the Universe
Short period comets
Spatial distribution
Spatial resolution
Sublimation
Wavelengths
Wirtanen comet
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Summary:Gas-phase molecules in cometary atmospheres (comae) originate primarily from (1) outgassing by the nucleus, (2) sublimation of icy grains in the near-nucleus coma, and (3) coma (photo)chemical processes. However, the majority of cometary gases observed at radio wavelengths have yet to be mapped, so their production/release mechanisms remain uncertain. Here we present observations of six molecular species toward comet 46P/Wirtanen, obtained using the Atacama Large Millimeter/submillimeter Array during the comet's unusually close (∼0.1 au) approach to Earth in 2018 December. Interferometric maps of HCN, CH3OH, CH3CN, H2CO, CS, and HNC were obtained at an unprecedented sky-projected spatial resolution of up to 25 km, enabling the nucleus and coma sources of these molecules to be accurately quantified. The HCN, CH3OH, and CH3CN spatial distributions are consistent with production by direct outgassing from (or very close to) the nucleus, with a significant proportion of the observed CH3OH originating from sublimation of icy grains in the near-nucleus coma (at a scale length Lp = 36 ± 7 km). On the other hand, H2CO, CS, and HNC originate primarily from distributed coma sources (with Lp values in the range 550–16,000 km), the identities of which remain to be established. The HCN, CH3OH, and HNC abundances in 46P are consistent with the average values previously observed in comets, whereas the H2CO, CH3CN, and CS abundances are relatively low.
ISSN:0004-637X
1538-4357
DOI:10.3847/1538-4357/ace0bc