Detection and characterization of Io's atmosphere from high-resolution 4-{\mu}m spectroscopy

•The first detection of Io’s SO2 atmosphere at 4.0μm is reported, providing a new window for Io’s atmospheric studies.•Our spatially-resolved data permit us a detailed characterization of Io’s atmosphere.•Longitudinal, diurnal, and latitudinal variations are observed.•A mean gas temperature of ∼170K is determined.