Short-Term Variability of Jupiter's Satellite Footprints as Spotted by JWST
By Katie Knowles (Northumbria University)
The James Webb Space Telescope (JWST) conducted a clockwise scan around the entire limb of Jupiter, chasing the northern lights, or aurora, as they rotated into view. This dynamic phenomenon is a result of charged particles traveling down magnetic field lines, crashing into the top of the atmosphere, or ionosphere, and causing it to glow. During its scan, JWST captured an extraordinary aspect of Jupiter's aurora, known as the auroral footprints, which are bright emission patterns produced as a result of the interaction between Jupiter's Galilean moons and the space environment surrounding the planet. Here, we present the first measurements of the physical properties of the auroral footprints of Jupiter's two innermost Galilean moons, Io and Europa, including the local temperature and ionospheric density, in the near-infrared. A never-seen-before low temperature structure was discovered, centred on Io's bright spot of emission, possessing extremely high densities. This is likely driven by extreme changes in the flow of electrons crashing into the upper atmosphere. Our analysis, as well as further endeavours, can supply context to in-situ measurements acquired by NASA's Juno spacecraft as it traversed within the moons' orbits, as well as for future investigations of the Galilean satellites, including the Jupiter Icy Moons Explorer (Juice) and Europa Clipper.
See publication for more details:
Knowles, K. L., Melin, H., Stallard, T. S., Moore, L., O’Donoghue, J., Schmidt, C., et al. (2026). Short-term variability of Jupiter's satellite footprints as spotted by JWST. Geophysical Research Letters, 53, e2025GL118553. https://doi.org/10.1029/2025GL118553

JWST/NIRSpec IFU observations of the auroral footprints of Io and Europa, indicated by yellow and purple arrows, respectively. We display the integrated H3+ spectral radiance with planetocentric latitude at 550 km above the 1-bar level (dotted) and System III (West) longitude (solid). UTC mid-points of integration are given above, and the circled numbers refer to the exposure label.