Isotopic Signature of Organic Molecules from Beyond the Solar System: An Enriched Methane D/H Ratio in the Interstellar Object 3I/ATLAS

TL;DR

This study reports a high deuterium/hydrogen ratio in methane from the interstellar object 3I/ATLAS, revealing formation in a cold, high D/H environment, distinct from our solar system's origins.

Contribution

First detection of deuterated organic molecules in an interstellar object, providing insights into its formation environment and chemical history.

Findings

D/H ratio in methane is (3.31±0.34)% in 3I/ATLAS.

D/H ratio is 14±2 times higher than in comet 67P.

Formation occurred in a cold, high D/H environment.

Abstract

Interstellar objects are interlopers from other planetary systems, and their volatile compositions provide a glimpse into planet formation around their host star. We present near-infrared spectra of the coma of interstellar object 3I/ATLAS measured with the James Webb Space Telescope. Our results demonstrate an unexpectedly high $\mathrm{D}/\mathrm{H} = (3.31\pm0.34)\%$ for methane and represent an exceedingly rare detection of deuterated organic molecules in an interstellar object. This D/H ratio is a factor of $14\pm2$ higher than that measured in comet 67P/Churyumov-Gerasimenko by the Rosetta spacecraft, the only other comet for which CH$_3$D has been detected, yet the ratio of deuteration in methane compared with water is consistent for both comets within $1.2\sigma$. The D/H ratio in methane is observationally unconstrained in extrasolar sources to date, but the enriched ratio in 3I/ATLAS is most similar to those measured in other organic molecules toward primitive environments. The high D/H ratios of water and methane in 3I/ATLAS are a natural consequence of formation in a high D/H elemental ratio environment as a result of locally cold conditions in the protoplanetary disk and prior interstellar cloud. Thus, 3I/ATLAS formed in an environment very different from that in which our Sun and planets originated.