Eclipse Observations of the Galilean Satellite Atmospheres
Abstract
The galilean satellites host atmospheres that are all extremely tenuous yet vary in composition and source between bodies, providing opportunities to study the generation of near-surface gas populations on small icy and rocky worlds located within intense particle environments. The oxygen-based atmospheres of Europa and Ganymede are sourced from the sputtering of surface ices, while Io's sulfur-based (SO2/SO) atmosphere is produced by a combination of volcanic outgassing and the sublimation of surface frosts. Studying these atmospheres is challenging from Earth because sunlight reflected off the satellites' high-albedo disks typically obscures the faint gas signatures. We present new observations of Io, Europa, and Ganymede made when the satellites were in eclipse by Jupiter and emissions from their tenuous atmospheres were therefore visible. The observations were made at the Keck and Hubble Space Telescopes on more than 10 occasions in 2015-2018. We present detections of the visible-wavelength oxygen aurorae of Europa and Ganymede, including the first detection of Europa's 6300 Angstrom oxygen aurora. Using these data, we derive column densities and place constraints on auroral morphology and variability. At Io we measure emission from volcanic SO gas at 1.7 microns; the factor of ten improvement to spectral resolution over all previous detections motivates detailed modeling, which indicates the presence of excited SO gas populations at both high and low temperatures. Together these observations form part of an ongoing campaign to investigate the composition and variability of the atmospheres of the galilean satellites.
- Publication:
-
AAS/Division for Planetary Sciences Meeting Abstracts #50
- Pub Date:
- October 2018
- Bibcode:
- 2018DPS....5040301D