High nitrogen and carbon isotopic ratios in the interstellar comet 3I/ATLAS

TL;DR

This study measures nitrogen and carbon isotopic ratios in interstellar comet 3I/ATLAS, revealing clues about its origin and the conditions of its formation environment, which differ from typical solar system comets.

Contribution

First isotopic ratio measurements in an interstellar object, providing new insights into its formation environment and origin.

Findings

Nitrogen isotopic ratio higher than typical solar system comets.

Carbon isotopic ratio marginally higher than in the interstellar medium.

Results suggest origin in the outer disc of an older low-metallicity star.

Abstract

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: $^{12}$C/$^{13}$C and $^{14}$N/$^{15}$N. We report $^{12}$C/$^{13}$C=$147^{+87}_{-40}$ and $^{14}$N/$^{15}$N=$343^{+454}_{-124}$. The $^{14}$N/$^{15}$N is higher than the value of $\sim$~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 $^{12}$C/$^{13}$C 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.