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 H+3 emission, temperature and column density are reported, as well as CH4 spectral radiance. At the Io footprint, H+3 temperatures are 670–900 K, excluding a spatially confined cold structure (538 +/- 17 K), localized to the MAW spot, with high densities (0.98 +/- 0.43 × 10¹⁶ m²). There are suggestions of a similar, less extreme H+3 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.