Presentation #103.02 in the session “A Plethora of Icy Satellites”.
Ground-based observations of Ganymede have revealed the surprising presence of condensed molecular oxygen (O2) via weak spectral features at visible wavelengths. To date, the state and stability of this O2 at the temperatures and pressures of Ganymede’s surface are not understood. Its geographic distribution compared to albedo, expected temperatures, particle irradiation patterns, or composition may provide clues to these unknowns. We present spatially resolved observations of Ganymede’s condensed surface O2 obtained with the Hubble Space Telescope and construct the first comprehensive map of its spatial distribution. In agreement with the limited spatially resolved data published previously, our map shows that the O2 is concentrated at the low to midlatitudes of the trailing hemisphere, which may reflect the influence of Ganymede’s intrinsic magnetic field in sheltering the trailing-hemisphere equator from charged-particle sputtering. Overlapping regions from different HST visits also show evidence for moderate temporal variability in the surface O2, which may reflect variations in the local magnetospheric environment. However, we are unable to distinguish between potential causes with the available data.