Ganymede's UV Reflectance From Juno-UVS Data

During the Juno orbit 34 Ganymede encounter, the ultraviolet spectrograph mapped UV sunlight reflected by Ganymede from a closest approach altitude of 1,044 km, allowing us to study spatial variations in Ganymede's far ultraviolet reflectance at higher resolution than has previously been possible. We find that a characteristic signature of water ice seen around 165 nm in laboratory spectra is absent over much of the observed area, but is detectable in the north high latitude region. We suggest that the spectral difference between the high latitudes and other icy regions, such as Tros crater, may be explained by the presence of additional UV-absorbing contaminants such as NH3 at lower latitudes. We also note a decrease in the relative reflectance of the high latitude regions at wavelengths >190 nm, which may be the start of a previously observed ozone absorption feature.