Prior to James Webb Space Telescope (JWST) observations of trans-Neptunian objects (TNOs), the surface compositions of the majority of TNOs were only poorly constrained. Ground-based spectroscopic observations in the visible and near-infrared allowed some positive detections of methane ice for the largest TNOs, while indications of water ice were seen more often among the population of small and intermediate objects. Methanol ice and ammoniated species were considered for a few objects. Theoretical models of Solar System formation and evolution, ice lines, and volatile retention still predicted that some outer Solar System objects could contain other species.
The JWST/NIRSpec instrument extended the spectroscopic observational window for the trans-Neptunian population out to 5 microns, and the JWST/MIRI instrument observed the Pluto-Charon system out to 25 microns. The observations performed during JWST's first cycle allowed us to see the first draft of the big picture formed by widespread carbon dioxide, detections of crystalline water ice, carbon monoxide, methanol, complex organic materials, by-products of methane ice irradiation, and nitrogen-rich compounds on TNOs of different sizes, albedos, and dynamical groups. In this presentation, we will show the connection between what was expected and what we see and how that could support the theoretical models of the formation and evolution of the outer Solar System.