Optical Spectroscopy of the Uranian Moons from Equinox to Northern Summer

We present an analysis of ground-based visible and near-infrared wavelength (VIS, ~0.4 -- 0.9 micron) reflectance spectra of the four largest Uranian satellites, utilizing observations with multiple telescopes, collected near Uranian equinox and in northern summer (2002 -- 2024). These data have much higher spectral resolution and signal-to-noise ratios compared to previously published optical spectra of the Uranian moons, collected primarily in the 1980s and 1990s. The higher spectral resolution of these new data allowed us to determine that the Uranian satellites exhibit distinct spectral slope variations across the VIS, supporting previous findings that the leading hemispheres of Titania and Oberon are redder than their respective trailing hemispheres. We find that the northern leading hemisphere of Titania appears to be redder than Oberon, and that Titania may have a larger leading/trailing asymmetry in reddening on its northern hemisphere compared to the other three large moons. We also conducted a sensitive search for subtle absorption features, finding no evidence of condensed O2 or other possible products of radiolytic processing. The non-detection of O2 suggests that charged particle interactions with the surfaces of the Uranian moons may be fairly limited, at least compared to the Galilean moons.