Nitrogen-bearing Species on Trans-Neptunian Objects Revealed by JWST/DiSCo-TNOs

Abstract C≡N-bearing species are valuable tracers of nitrogen chemistry in the solar system. Ranging from volatile compounds like HCN and CH 3 CN in cometary comae to refractory CN-bearing organics in some micrometeorites and interplanetary dust particles, these species originate in, or are derived from, molecular precursors in the interstellar medium (ISM). The icy surfaces of medium-sized trans-Neptunian objects (TNOs) represent an intermediate stage in the chemical evolution and incorporation of N-bearing molecules from the ISM into the solar system. Herein, we investigate the nature, distribution, and origin of CN-bearing species on several TNOs and one centaur observed within the James Webb Space Telescope DiSCo-TNOs program. We find a spectral feature at 4.62 μm consistent in band position and width as OCN − observed in the ISM and the laboratory. This feature is most pronounced on TNOs in the Cliff2 group (Cliff2-TNOs, a compositional subgroup characterized by low ice content that include the cold classical TNOs, suggesting they formed farthest from the Sun) and might be tracing an original chemical inventory in the protoplanetary disk. Cliff2-TNOs are also the best candidates for studying the contribution of refractory C≡N-containing organics to a broad 4.5 µm spectral feature. Finally, a close spectral resemblance between Cliff2-TNOs and the centaur in our analysis, which exhibits both the 4.62 and 4.5 μm bands, provides a plausible dynamical channel that can enrich the inner solar system with N-bearing species. Our work advances the understanding of N-bearing species in the solar system and their evolutionary history beginning in the ISM.