Evidence for Surprising Heavy Nitrogen Isotopic Enrichment in Comet 46P/Wirtanen's Hydrogen Cyanide

M. A. Cordiner; K. Darnell; D. Bockeleé-Morvan; N. X. Roth; N. Biver; S. N. Milam; S. B. Charnley; J. Boissier; B. P. Bonev; C. Qi; J. Crovisier; A. J. Remijan

arXiv · 2409.05711

Evidence for Surprising Heavy Nitrogen Isotopic Enrichment in Comet 46P/Wirtanen's Hydrogen Cyanide

M. A. Cordiner·K. Darnell·D. Bockeleé-Morvan·N. X. Roth·N. Biver·S. N. Milam·S. B. Charnley·J. Boissier·B. P. Bonev·C. Qi·J. Crovisier·A. J. Remijan

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Abstract

46P/Wirtanen is a Jupiter-family comet, probably originating from the Solar System's Kuiper belt, that now resides on a 5.4 year elliptical orbit. During its 2018 apparition, comet 46P passed unusually close to the Earth (within 0.08 au), presenting an outstanding opportunity for close-up observations of its inner coma. Here we present observations of HCN, H$^{13}$CN and HC$^{15}$N emission from 46P using the Atacama Compact Array (ACA). The data were analyzed using the SUBLIME non-LTE radiative transfer code to derive $^{12}$C/$^{13}$C and $^{14}$N/$^{15}$N ratios. The HCN/H$^{13}$CN ratio is found to be consistent with a lack of significant $^{13}$C fractionation, whereas the HCN/HC$^{15}$N ratio of $68\pm27$ (using our most conservative $1\sigma$ uncertainties), indicates a strong enhancement in $^{15}$N compared with the solar and terrestrial values. The observed $^{14}$N/$^{15}$N ratio is also significantly lower than the values of $\sim140$ found in previous comets, implying a strong $^{15}$N enrichment in 46P's HCN. This indicates that the nitrogen in Jupiter-family comets could reach larger isotopic enrichments than previously thought, with implications for the diversity of $^{14}$N/$^{15}$N ratios imprinted into icy bodies at the birth of the Solar System.

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M. A. Cordiner, K. Darnell, D. Bockeleé-Morvan, N. X. Roth, N. Biver, S. N. Milam, S. B. Charnley, J. Boissier, B. P. Bonev, C. Qi, J. Crovisier, A. J. Remijan. 2024-09-09. Evidence for Surprising Heavy Nitrogen Isotopic Enrichment in Comet 46P/Wirtanen's Hydrogen Cyanide. https://arxiv.org/abs/2409.05711

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