Short-Term Variability of Jupiter's Satellite Footprints as Spotted by JWST

We present the main Alfvén wing (MAW) spots of Io and Europa as observed by the Near-Infrared Spectrograph onboard the James Webb Space Telescope. These auroral footprint features have been measured previously, but only in emission. Here, the derived ionospheric (Formula presented.) emission, temperature and column density are reported, as well as (Formula presented.) spectral radiance. At the Io footprint, (Formula presented.) temperatures are 670–900 K, excluding a spatially confined cold structure (538 (Formula presented.) 17 K), localized to the MAW spot, with high densities (0.98 (Formula presented.) 0.43 × (Formula presented.)). There are suggestions of a similar, less extreme (Formula presented.) population associated with the Europa footprint. However, temperatures at Io's MAW spot show significant variability within different observational exposures, indicating precipitation energy changes, sampling various regions of the ionosphere's altitudinal temperature profile. This work provides a new window into understanding the auroral processes driven by moon-magnetosphere interactions in the Jovian system.