Date: 2025-10-03 00:00:00
Time: 3:30 – 4:30pm
Location: 3853 Slichter Hall
Presented By:
Zac Milby
Abstract:
The optical aurorae of Jupiter’s Galilean satellites are generated and maintained through a variety of processes. On Io, a combination of volcanism and sublimation produces its SO₂-dominated atmosphere. On the icy satellites Europa, Ganymede, and Callisto, sublimation and sputtering produce O₂-dominated atmospheres. Unfortunately, in situ observations have been limited to brief spacecraft flybys by missions focusing on Jupiter or those just passing through the system. Consequently, most of our knowledge of their atmospheric compositions has come from Earth-based UV observations using the Hubble Space Telescope. However, its small mirror size and orbital properties limit the signal-to-noise achievable and prevent HST observations from revealing short-timescale variability.
For the past four years, we have been observing Jupiter’s Galilean satellites using the HIRES instrument on the Keck I telescope at the summit of Maunakea, Hawaii. This instrument’s wavelength sensitivity allows us to simultaneously observe a variety of bright optical auroral emissions, and the large mirror of the Keck I telescope enables high-cadence observations with good signal-to-noise. In comparison to the UV emissions observable with HST, the larger number of optical lines allows us to place more robust constraints on atmospheric composition. We must also take the observations in eclipse to suppress reflected sunlight from their icy surfaces, as this limits the excitation of the auroral emissions by magnetospheric electrons, providing a remote-sensing window into the interaction between the satellites and their local plasma environment. In this talk, I will discuss what these observations have revealed about each satellite’s atmosphere and provide insights into the properties of the electrons exciting their auroral emissions.