http://arxiv.org/abs/2305.04822
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, CH$_3$OH, CH$_3$CN, H$_2$CO, 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, CH$_3$OH and CH$_3$CN spatial distributions are consistent with the production from direct outgassing from (or very near to) the nucleus, with a significant proportion (~50%) of the observed CH$_3$OH originating from sublimation of icy grains in the near-nucleus coma. On the other hand, H$_2$CO, CS and HNC originate primarily from distributed coma sources. The HCN, CH$_3$OH and HNC abundances in 46P are consistent with the average values previously observed in comets, whereas the H$_2$CO, CH$_3$CN and CS abundances are relatively low.
M. Cordiner, N. Roth, S. Milam, et. al.
Tue, 9 May 23
33/88
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