Molecular mapping of comet 46P/Wirtanen using ALMA: parent vs. daughter sources in the coma
Martin Cordiner 1,2 , Stefanie Milam 1 , Nathan Roth 1,2, Steven Charnley 1 , Boncho Bonev 3 , Dominique Bockelee-Morvan 4 , Nicolas Biver 4 , Jeremie Boissier 5 , Anthony Remijan 6 1 Astrochemistry Laboratory, NASA Goddard Space Flight Center, 8800 Greenbelt Road, Greenbelt, MD 20771, USA, 2 Department of Physics, Catholic University of America, Washington, DC 20064, USA, 3 Department of Physics, American University, Washington D.C., USA, 4 LESIA, Observatoire de Paris, 5 place Jules Janssen, F-92195 Meudon, France, 5 Institut de Radioastronomie Millimetrique, 300 rue de la Piscine, F-38406, Saint Martin d'Heres, France, 6 National Radio Astronomy Observatory, Charlottesville, VA 22903, USA. Molecules observed in cometary comae originate primarily from (1) outgassing by the nucleus, (2) sublimation of icy grains in the near-nucleus coma, and (3) gas-phase coma (photo-)chemistry. However, the majority of cometary gases observed at radio wavelengths have yet to be mapped, so their production mechanisms remain uncertain. Here we present ALMA observations of six molecular species towards comet 46P/Wirtanen, obtained during the comet's extremely close (~0.1 au) approach to Earth in December 2018. Emission maps of HCN, HNC, CH3OH, CH3CN, H2CO and CS were obtained at an unprecedented spatial resolution of up to 25 km, enabling the nucleus and coma sources of these molecules to be investigated. Asymmetric outgassing from the comet was modeled using our 3D, non-LTE radiative transfer code (SUBLIME). The HCN, CH3OH and CH3CN spatial distributions are found to be consistent with the majority of their production coming from direct outgassing by the nucleus, whereas CS, HNC and H2CO originate primarily from (distributed) coma sources.
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© The Author(s), 2023
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