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

Abstract

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 towards comet 46P/Wirtanen, obtained using the Atacama Large Millimeter/submillimeter Array (ALMA) during the comet's unusually close (~0.1 au) approach to Earth in December 2018. 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 near 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 $L_p=36\pm 7$ km). On the other hand, H2CO, CS and HNC originate primarily from distributed coma sources (with $L_p$ 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.

arXiv commentAccepted for publication in the Astrophysical Journal on 2023-06-17

References in corpus (39)

• CASA, the Common Astronomy Software Applications for Radio Astronomy
• Observations of the Icy Universe
• The Cologne Database for Molecular Spectroscopy, CDMS, in the Virtual Atomic and Molecular Data Centre, VAMDC
• Photodissociation and photoionisation of atoms and molecules of astrophysical interest
• An Ice Age JWST inventory of dense molecular cloud ices
• The cometary composition of a protoplanetary disk as revealed by complex cyanides
• Astrochemistry and compositions of planetary systems
• LIME - a flexible, non-LTE line excitation and radiation transfer method for millimeter and far-infrared wavelengths
• H-atom addition and abstraction reactions in mixed CO, H2CO and CH3OH ices: an extended view on complex organic molecule formation
• Cometary Chemistry and the Origin of Icy Solar System Bodies, the view after Rosetta
• Ammonium salts are a reservoir of nitrogen on a cometary nucleus and possibly on some asteroids
• A Distribution of Large Particles in the Coma of Comet 103P/Hartley 2
• Water Ice and Dust in the Innermost Coma of Comet 103P/Hartley 2
• A Survey of CH3CN and HC3N in Protoplanetary Disks
• The Composition of Comets
• Unusually High CO Abundance of the First Active Interstellar Comet
• Detecting Weak Spectral Lines in Interferometric Data through Matched Filtering
• Terrestrial deuterium-to-hydrogen ratio in water in hyperactive comets
• Mapping the release of volatiles in the inner comae of comets C/2012 F6 (Lemmon) and C/2012 S1 (ISON) using the Atacama Large Millimeter/Submillimeter Array
• Interferometric imaging of the sulfur-bearing molecules H2S, SO and CS in comet C/1995 O1 (Hale-Bopp)
• Molecules with ALMA at Planet-forming Scales (MAPS) VI: Distribution of the small organics HCN, C2H, and H2CO
• The gas production of 14 species from comet 67P/Churyumov-Gerasimenko based on DFMS/COPS data from 2014-2016
• An ALMA Survey of H${}_2$CO in Protoplanetary Disks
• Molecules with ALMA at Planet-forming Scales (MAPS). IX. Distribution and Properties of the Large Organic Molecules HC${}_3$N, CH${}_3$CN, and $c$-C${}_3$H${}_2$
• Hydrogen Isocyanide in Comet 73P/Schwassmann-Wachmann (Fragment B)
• HIFI Observations of Water in the Atmosphere of Comet C/2008 Q3 (Garradd)
• Molecular composition of comet 46P/Wirtanen from millimetre-wave spectroscopy
• ALMA mapping of rapid gas and dust variations in comet C/2012 S1 (ISON): new insights into the origin of cometary HNC
• Molecular investigations of comets C/2002 X5 (Kudo-Fujikawa), C/2002 V1 (NEAT), and C/2006 P1 (McNaught) at small heliocentric distances
• A SUBLIME 3D Model for Cometary Coma Emission: the Hypervolatile-Rich Comet C/2016 R2 (PanSTARRS)
• The Sources of HCN and CH3OH and the Rotational Temperature in Comet 103P/Hartley 2 from Time-Resolved Millimeter Spectroscopy
• Thermal processing of Jupiter Family Comets during their chaotic orbital evolution
• No compelling evidence of distributed production of CO in comet C/1995 O1 (Hale-Bopp) from millimeter interferometric data and a reanalysis of near-IR lines
• ALMA Autocorrelation Spectroscopy of Comets: The HCN/H^13CN ratio in C/2012 S1 (ISON)
• Thermal physics of the inner coma: ALMA studies of the methanol distribution and excitation in comet C/2012 K1 (PanSTARRS)
• Activity and composition of the hyperactive comet 46P/Wirtanen during its close approach in 2018
• Emission from HCN and CH${}_3$OH in comets. Onsala 20-m observations and radiative transfer modelling
• Neutral-Neutral Synthesis of Organic Molecules in Cometary Comae
• GALEX Observations of CS and OH Emission in Comet 9P/Tempel 1 During Deep Impact

Cited by in corpus (5)

• A D/H Ratio Consistent with Earth's Water in Halley-type Comet 12P from ALMA HDO Mapping
• First Detection of Molecular Activity in the Largest Known Oort Cloud Comet: ALMA Imaging of C/2014 UN271 (Bernardinelli-Bernstein) at 16.6 au from the Sun
• FAST Observations of Four Comets to Search for the Molecular Line Emissions between 1.0 and 1.5 GHz Frequencies
• ALMA and GMRT Studies of Dust Continuum Emission and Spectral Lines Toward Oort Cloud Comet C/2022 E3 (ZTF)
• Collisional Excitation in Space: Recent Advances and Future Challenges in the JWST Era