IntroductionThe C≡N functional group (hereafter CN) can be incorporated into a diverse range of molecular structures, ranging from simpler cyanides like HCN to semi-refractory salts like NH4+OCN- and larger and more complex polymeric refractory material. In astrophysical settings, CN-bearing compounds form and evolve through thermal, photochemical, and radiation-driven chemical pathways. Consequently, these species serve as valuable tracers for accessing the current and past physical conditions of astrophysical environments and provide a framework for understanding the evolution of nitrogen in space.The cycle 1 JWST program "Discovering the Surface Composition of TNOs" (DiSCo-TNOs; #2418; P.I.: N. Pinilla-Alonso) has detected spectral features due to the CN functional group on several medium-sized trans-Neptunian objects (TNOs), whose icy surfaces could be key to unlocking the chemical and physical relationship among small bodies in the Solar System and their evolutionary history beginning in the interstellar medium (ISM). An early DiSCo result found a first spectral feature at 4.62 µm, tentatively assigned to OCN-, and a second and more elusive feature near 4.5 µm, attributed to the CN group incorporated into an organic chemical structure. The former has been detected previously in many astrophysical environments, including dense molecular clouds [1], young stellar objects [2], and protoplanetary disks [3], while the latter has been observed on Callisto [4] and rare nitrogen-rich interplanetary dust particles and ultracarbonaceous Antarctic micrometeorites [5,6].The DiSCo-TNOs program established a significant connection between TNO surface composition and formation location in the outer protoplanetary disk, establishing ice retention lines for H2O, CO2, and CH3OH [7]. The implication of CN-bearing compounds in understanding the molecular diversity of the past and current Solar System are the topic of the current investigation.Aim & Method In this work, we revisit the 4.62 and 4.5 µm features observed within the DiSCo-TNOs program and measure their distribution across the dataset. We modeled the spectra of 37 TNOs and 1 centaur between 4.35 and 4.75 μm using four Gaussian components—13CO2 (at 4.38 μm), a 4.5 μm feature, a 4.62 μm feature, and CO (at 4.68 μm)—to disentangle the influence of adjacent bands and extract the parameters of the 4.5 and 4.62 μm features (Figure 1). Then, using existing observational and laboratory data, as well as investigating their relationship with other spectral features, we aimed to: (1) constrain the molecular carriers responsible for the 4.62 and 4.5 µm bands; (2) elucidate their origin on TNOs; and (3) place them in the broader context of nitrogen in the Solar System.Results & DiscussionOur analysis finds that both the 4.62 and 4.5 µm features exhibit the strongest band areas on a group of TNOs rich in CH3OH and other organics (also known as Cliff-TNOs), with the 4.62 µm feature being particularly strong on a subset of these TNOs (also called Cliff2-TNOs) which include the Cold Classical population formed farthest from the Sun in the protoplanetary disk. These Cliff2-TNOs show notably weaker spectral signatures of H2O, CH3OH, and CO2 ices compared to Cliff1-TNOs [8].A careful comparison of the 4.62 µm band in our data with previous ISM observations and laboratory spectra confirm its attribution to OCN-. This constitutes one of the first definitive detections of a minor species traced from molecular clouds and protoplanetary disks to TNOs. Further, the strong OCN- feature in spectra also poor in water and other ices provides compelling evidence that the composition of TNOs differs significantly from the ice abundances in the ISM and indicates that local processes influenced their molecular inventories. We explore several origin scenarios of OCN- on DiSCo-TNOs, favouring an inheritance from the protoplanetary disk as the most plausible explanation.The 4.5 µm feature shares a common band profile to complex organic CN-bearing residues produced in the laboratory (e.g. tholin), though contributions from methanol and carbon chain oxides cannot be ruled out in some spectra. We interpret the refractory CN-bearing material as a tracer of the outer protoplanetary disk before or shortly after planetesimal formation. The poor signal-to-noise ratio in this spectral region precludes a clear origin scenario.Finally, the detection of the 4.62 and 4.5 µm features on the centaur in our dataset acts as a critical observation for connecting nitrogen-rich environments across the Solar System. Centaurs are transient objects that dynamically bridge the TNO reservoir to the Jupiter-family comets and recent work suggests that at least a subset of these bodies originate from the Cliff-TNO population [9]—those rich in methanol and other organics and where we detect the 4.62 and 4.5 µm features most abundantly. We propose that the Cliff-TNO population may serve as a primary reservoir for the nitrogen-rich dust grains observed on some comets, interplanetary dust particles, and micrometeorites. Therefore, our work has important implications for drawing broader chemical and dynamical pathways that connect small bodies across the Solar System.Figure 1. Example of the four-component Gaussian fitting method used to extract the band parameters of the 4.62 and 4.5 µm spectral features. Vertical lines mark features due to 13CO2, the 4.5 μm feature, the 4.62 μm feature, and CO.References[1] McClure, M.K. et al. (2023) Nat. Astron., 7, 431. [2] Pendleton, Y. J. et al. (1999) ApJ, 513, 291. [3] Sturm, J. A. (2023) A&A, 679, A138. [4] Cartwright, R. J. et al. (2024) Planet. Sci. J. 5, 60. [5] Dobrică, E. et al. (2011) M&PS, 46, 1363. [6] Dartois, E. et al. (2013) Icarus, 224, 243. [7] Pinila-Alonso, N. et al. (2024) Nat. Astron., 9, 230. [8] Brunetto, R. et al. (2025) ApJL, 982, L8. [9] Licandro et al. (2024) Nat. Astron., 9, 245.