A detection of CO₂ gas on the Valhalla-centered observation using JWST. Left panel: A slice of the disk-integrated NIRSpec spectrum containing the 4.25 µm absorption feature (black). This absorption feature is dominated by solid-phase CO₂ to which a continuum was fit (red). The subtraction of the continuum from the data reveals the much weaker gas-phase signal (black, bottom). The fit of the CO₂ gas-phase model is shown in orange. Right panel: The column density of CO₂ gas across Callisto’s disk.