1998/05/20 by D. T. Hall, P. D. Feldman, M. A. McGrath +1 · 3 citations
Physics and Astronomy · Earth and Planetary Sciences · #Astro and Planetary Science #Ionosphere and magnetosphere dynamics #Atmospheric Ozone and Climate
paper · pdf · doi:10.1086/305604
openalex publication_date 1998/05/20 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/04
Far-UV spectra of Europa and Ganymede, acquired by the Hubble Space T elescope Goddard High Resolution Spectrograph, indicate that, in addition to faintly reflected sunlight, both satellites emit O I 1304 Å and O I 1356 Å airglow radiation. The observed brightnesses of the reflected solar C II 1335 Å feature indicate that the disk-averaged albedos of Europa and Ganymede are about 1.5% and 2.6%, respectively. Airglow emissions from both satellites are characterized by the flux ratio F (1356 Å)/ F (1304 Å) of roughly 1-2, diagnostic of dissociative electron impact excitation of O 2 . Inferred O 2 vertical column densities are in the range (2.4-14) × 10 14 cm -2 for Europa and (1-10) × 10 14 cm -2 for Ganymede. The observed double-peaked profile of Ganymede's O I 1356 Å feature indicates a nonuniform spatial emission distribution that suggests two distinct and spatially-confined emission regions, consistent with the satellite's north and south poles.