The complex surface and atmospheric properties of Triton revealed by JWST/NIRSpec

The Kuiper belt holds the key to understanding the primordial environment within the outermost reaches of the protoplanetary disk. For decades, only the largest members of this population - the dwarf planets - were amenable to detailed characterization. While recent advances in telescope capabilities have widened the purview of spectroscopic exploration in the Kuiper belt, the dwarf planets continue to serve as important beacons for our investigations of the outer Solar System. Triton is an irregular satellite of Neptune that was captured from the Kuiper belt. With a diameter of 2710 km, it is the largest Trans-Neptunian Object (TNO) and one of only three large TNOs that have been visited by spacecraft. The 1989 Voyager 2 flyby revealed a highly inhomogeneous surface, evidence for cryovolcanism, and a tenuous nitrogen-dominated atmosphere, indicating complex surface processes and a complicated evolutionary history. Subsequent observations have produced detections of many ice species (CH4, CO2, CO, N2, H2O) and evidence for time-varying behavior in Triton's atmosphere. In this talk, we present new near-infrared spectra of Triton that were collected as part of Guaranteed Time Observations during the first year of JWST science operations (PID 1272; PI: Dean Hines). Triton was observed twice with the NIRSpec instrument using the high-resolution gratings, yielding exquisite spectra of the trailing and leading hemispheres spanning 0.9-5.3 µm at a spectral resolving power of R~2700. The spectra are rich in ice absorption features across the full wavelength range. The detected feature set of CO2 ice is particularly extensive, with at least a dozen overtone and combination bands present. In addition, we report several isotopologue species, including CH3D, 13CO2, 12C18O2, and 13CO, from which we estimate the D/H, 13C/12C, and 18O/16O isotope ratios. Lastly, we have uncovered emission bands from atmospheric CO fluorescence at 4.7-4.9 µm. We describe detailed compositional modeling of the surface and atmosphere, place the JWST spectra in the context of previous telescope observations, and discuss the implications for the formation and evolutionary history of Triton and the Kuiper belt at large.