The Geographic Distribution of Dense-phase O₂ on Ganymede

Abstract

Ground-based spectroscopy of Ganymede's surface has revealed the surprising presence of dense-phase molecular oxygen (O₂) via weak absorptions 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 spatial distribution in relation to albedo, expected temperatures, particle irradiation patterns, or composition may provide clues to these unknowns. We present spatially resolved observations of Ganymede's surface O₂ obtained with the Hubble Space Telescope and construct the first comprehensive map of its geography. In agreement with the limited spatially resolved data published previously, our map suggests that the condensed O₂ is concentrated at the low to midlatitudes of the trailing hemisphere, a distribution that may reflect influences of Ganymede's intrinsic magnetic field on the bombardment of its surface by Jovian magnetospheric particles. Overlapping regions from different observations within this data set also show evidence for moderate temporal variability in the surface O₂, but we are unable to distinguish between potential causes with the available data.