Hubble Space Telescope observations of Ganymede in eclipse of Jupiter

This thesis investigates the detection and characterization of Lyman-alpha emissions in Ganymede’s atmosphere during eclipse by Jupiter, focusing on the hydrogen exosphere and potential auroral emissions. Observing Lyman-alpha during eclipse reduces interference from reflected solar flux, enabling the study of faint atmospheric processes. The study addresses three main questions: (1) Can a Lyman-alpha signal from Ganymede’s surface be detected during eclipse, and if so, what can it be attributed to? (2) Probing impact- driven electron excitation, can Lyman-alpha emissions be discerned in the auroral regions during eclipse? (3) How does the resonantly scattered emissions in Ganymede’s hydrogen exosphere respond to eclipse conditions?
The observations, spanning from October 2022 to September 2024, cover significant portions of the eclipse phases and reveal that disk emissions are consistent with expected reflected interplanetary radiation, with no additional emission sources required to explain the signal.