Discovery of an elevated 15N/14N ratio in the Jupiter-family comet 46P/Wirtanen using ALMA K. J. Darnell 1 , M. A. Cordiner 1 , S. N. Milam 1 , N. X. Roth 1 , S. B. Charnley 1 , A. J. Remijan 2 , D. Bockelee-Morvan 3 , N. Biver 3 1 Astrochemistry Laboratory, NASA Goddard Space Flight Center, 8800 Greenbelt Road, Greenbelt, MD 20771, USA. 2 National Radio Astronomy Observatory, Charlottesville, VA 22903, USA. 3 LESIA, Observatoire de Paris, 5 place Jules Janssen, F-92195 Meudon, France. 46P/Wirtanen is a Jupiter Family comet with a short (5.4 year) orbital period. During its last apparition in 2018, it passed unusually close to the Earth (within 0.08 au), presenting an outstanding opportunity for close-up observations of its inner coma. We used the Atacama Large Millimeter/submillimeter Array (ALMA) to obtain detailed, interferometric observations of 46P in the 243-366 GHz spectral range near the comet's closest approach in December 2018, resulting in an unprecedented sky-projected spatial resolution of up to 25 km. Spectral imaging of multiple molecules was performed, and these data were analyzed using our latest non-LTE radiative transfer code (SUBLIME), to determine the detailed physical and chemical structure of the coma. In this poster, we present images and spectra of the HCN, H 13 CN and HC 15 N molecules, from which the 12 C/ 13 C and 14 N/ 15 N ratios are derived. The results are found to be consistent with a lack of significant 13 C fractionation in cometary nitriles, whereas the 14 N/ 15 N ratio indicates an enhancement in 15 N compared with protosolar (~440) and terrestrial values (~270). The ratio also appears to be lower than previously observed in other comets (~140), implying a significant 15 N enrichment in 46P's HCN. This indicates that the nitrogen in Jupiter-family comets could be more enriched in 15 N than previously thought.
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