HST/STIS observations and simulation of Io's emission spectrum in Jupiter shadow: Probing Io's Jupiter-facing eclipse atmosphere

► Io's MUV aurorae have been observed and simulated in eclipse. ► Emission from SO2, SO, and S I has been detected and simulated. ► The emission is consistent with dissociative excitation of SO2 by torus electrons. ► A spectrum from an unidentified species was discovered. ► As much as a 5% non-thermal component to the torus electrons in implied.