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Parent and Daughter Outgassing from Comet 46P/Wirtanen Mapped using ALMA

Presentation #400.02 in the session Comets: Coma (Oral Presentation)

Published onOct 23, 2023
Parent and Daughter Outgassing from Comet 46P/Wirtanen Mapped using ALMA

Molecules observed in cometary atmospheres (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 in the coma of 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), revealing the presence of enhanced coma expansion velocities and molecular production rates on the sunward side of the nucleus. 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 (or from near-nucleus icy grains, in the case of CH3OH), whereas CS, HNC and H2CO originated primarily from distributed coma sources. The abundances of HCN and CH3OH in comet 46P are consistent with average values found in OCCs and JFCs. On the other hand, CH3CN, H2CO and CS are at the lower end of the range of previously observed abundances, consistent with a depletion of these species (or their parents) in the 46P nucleus.

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