Space Telescope Imaging Spectrograph Observations of Europa’s Optical Aurora

Abstract We analyzed Hubble Space Telescope observations of Europa’s optical aurora, yielding further insight into the composition of its tenuous atmosphere and its plasma-interaction variability. We obtained these observations of auroral emissions while Europa was in solar eclipse behind Jupiter to avoid reflected sunlight as a background signal and source of noise. We analyzed oxygen 630.0 and 636.4 nm emission line brightness profiles across the disk to constrain O 2 abundances. Analyses of time-varying brightness ratios across different regions of Europa were compared with previous auroral studies in the ultraviolet and in the visible. We confirm a correlation with auroral brightness and relative distance from Jupiter’s plasma sheet crossing. We find that the decorrelated set of auroral brightnesses diminishes with longer eclipse duration, suggesting a possible partial collapse of Europa’s atmosphere when in eclipse.