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

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, H¹³CN and HC¹⁵N emission from 46P using the Atacama Compact Array (ACA).

The data were analyzed using the SUBLIME non-LTE radiative transfer code to derive ¹²C/¹³C and ¹⁴N/¹⁵N ratios. The HCN/H¹³CN ratio is found to be consistent with a lack of significant ¹³C fractionation, whereas the HCN/HC¹⁵N ratio of 68±27 (using our most conservative 1σ uncertainties), indicates a strong enhancement in ¹⁵N compared with the solar and terrestrial values.

The observed ¹⁴N/¹⁵N ratio is also significantly lower than the values of ∼140 found in previous comets, implying a strong 15N 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 ¹⁴N/¹⁵N ratios imprinted into icy bodies at the birth of the Solar System.

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

Comments: Accepted for publication in PSJ, September 2024
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2409.05711 [astro-ph.EP] (or arXiv:2409.05711v1 [astro-ph.EP] for this version)
https://doi.org/10.48550/arXiv.2409.05711
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Submission history
From: Martin Cordiner PhD
[v1] Mon, 9 Sep 2024 15:22:32 UTC (1,261 KB)
https://arxiv.org/abs/2409.05711
Astrobiology, Astrochemistry,