Overview
- Published March 3, 2026 in Geophysical Research Letters, the work uses JWST NIRSpec data from a 22-hour limb scan in September 2023 to deliver the first infrared spectral measurements of Io’s and Europa’s footprints.
- Spectra show a previously unseen cold feature within Io’s footprint at about 538 K compared with roughly 766 K in Jupiter’s main aurora, co-located with about triple the H3+ density.
- H3+ densities within the footprints reach around three times those of the main aurora, with localized variations up to roughly 45-fold over minutes, indicating rapidly changing electron precipitation.
- The cold, high-density structure was captured in only one of five JWST snapshots, so its prevalence and triggers remain uncertain.
- To test frequency and behavior, the team secured more than 32 hours on NASA’s Infrared Telescope Facility in Hawaii in January 2026, with analysis ongoing and comparative questions raised for other moon–planet systems such as Saturn–Enceladus.