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Short-Timescale Variability of Ganymede’s Optical Aurora

Presentation #210.06 in the session Ocean Worlds: Tectonics, Surfaces, and Ionospheres (Oral Presentation)

Published onOct 23, 2023
Short-Timescale Variability of Ganymede’s Optical Aurora

The thin atmosphere of Ganymede can be studied remotely through its auroral emissions. Most studies to date have used space-based ultraviolet observations of neutral oxygen aurora at 130.4 and 135.6 nm. Last year we reported the discovery of optical aurora on Ganymede using average disk-integrated results over several nights of observation with Keck/HIRES. These results supported an O2-dominated atmosphere with no evidence of H2O. We’ve now extended our previous optical wavelength work to a time-series analysis of the spatial and temporal variability of Ganymede’s aurora. Unlike the other Galilean satellites, Ganymede’s internally-generated magnetic field influences the brightness and spatial distribution of the aurora, resulting in auroral ovals near the geographic poles similar to Earth. We observed north/south hemispheric brightness asymmetries correlating with Ganymede’s position relative to the mid-plane of the jovian plasma sheet and spatial distributions correlating with the positions of the auroral ovals. We also had sufficient signal-to-noise in individual observations to search for short-timescale variability in atmospheric composition during the onset of the eclipse. While we detected variability in the brightness of the aurora on ~10 minute timescales, we did not detect any variability in atmospheric composition over the ~2 hour duration of the eclipse.

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