Leveraging the ALMA Atacama Compact Array for Cometary Science: An Interferometric Survey of Comet C/2015 ER61 (PanSTARRS) and Evidence for a Distributed Source of Carbon Monosulfide

We report the first survey of molecular emission from cometary volatiles using standalone Atacama Compact Array (ACA) observations Large Millimeter/Submillimeter (ALMA) toward comet C/2015 ER61 (PanSTARRS) carried out on UT 2017 April 11 and 15, shortly after its 4 outburst. These measurements HCN, CS, CH3OH, H2CO, HNC (along with continuum dust) probed inner coma ER61, revealing asymmetric outgassing discerning parent daughter/distributed source species. This work presents spectrally integrated flux maps, autocorrelation spectra, production rates, scale lengths for each molecule a stringent upper limit CO. HCN is consistent direct nucleus release in whereas HNC, potentially CH3OH are associated distributed sources coma. Adopting Haser model, determined H2CO (Lp ∼ 2200 km) 3300 previous comets, significant extended 2000 indicated suggesting an unknown The point-source distribution density implying excessively large nucleus, inconsistent other estimates size. It best explained by thermal slowly moving outburst ejectas, total mass 5–8 × 1010 kg. results demonstrate power ACA abundances, spatial distributions, locations moderately bright comets such as ER61.