High Nitrogen And Carbon Isotopic Ratios In The Interstellar Comet 3I/ATLAS

Interstellar objects provide a unique opportunity to further our understanding of the planetary formation process by studying in detail material formed around another star. Their ices contain precious clues about the environment and conditions prevailing in their home system.

As fractionation processes can be sensitive to the temperature and radiation environment, isotopic ratios are powerful tracers of the origin and evolution of different species. While isotopic ratios have been measured in solar system comets, previously detected interstellar objects have been too faint to measure isotopic ratios. Here we report the measurement of two ratios in 3I/ATLAS from observations of the CN molecule: ¹²C/¹³C and ¹⁴N/¹⁵N.

We report ¹²C/¹³C=147+87−40 and ¹⁴N/¹⁵N=343+454−124. The ¹⁴N/¹⁵N is higher than the value of ∼~150 usually measured for solar system comets, close to the values measured in the interstellar medium, pre-stellar phases or the outside of protoplanetary discs.

The ¹²C/¹³C is marginally higher than the values usually measured for solar system comets and in the interstellar medium. These measurements could indicate an origin of 3I in the outer disc around an older low-metallicity star.

C. Opitom, J. Manfroid, D. Hutsemékers, E. Jehin, M. M. Knight, K. Aravind, L. Ferellec, D. Bodewits, V. V. Guzmán, M. Cordiner, R. C. Dorsey, F. La Forgia, M. Lippi, B. P. Murphy, C. Snodgrass, M. Bannister

Comments: Submitted for publication to Nature
Subjects: Earth and Planetary Astrophysics (astro-ph.EP); Astrophysics of Galaxies (astro-ph.GA)
Cite as: arXiv:2603.07187 [astro-ph.EP] (or arXiv:2603.07187v1 [astro-ph.EP] for this version)
https://doi.org/10.48550/arXiv.2603.07187
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Submission history
From: Cyrielle Opitom
[v1] Sat, 7 Mar 2026 12:58:22 UTC (295 KB)
https://arxiv.org/abs/2603.07187
Astrobiology, Astrochemistry,