  Ground-based spectroscopy of Ganymede's surface has revealed the surprising
presence of dense-phase molecular oxygen (O$_2$) via weak absorptions at
visible wavelengths. To date, the state and stability of this O$_2$ 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 O$_2$ 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 O$_2$ is concentrated at the
low- to mid-latitudes 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 our dataset also show evidence for moderate
temporal variability in the surface O$_2$, but we are unable to distinguish
between potential causes with the available data.
