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We propose to observe the large Uranian satellites Ariel comma Umbriel comma Titania comma and Oberon comma using the Space Telescope Imaging Spectrograph (STIS) on the Hubble Space Telescope (HST) comma to investigate whether their surface compositions are modified by charged particles trapped in Uranus. magnetosphere. The large Uranian moons are candidate ocean worlds comma with surfaces that are rich in CO2 ice. The origin of CO2 ice on these moons is uncertain comma but it could be formed by ongoing charged particle bombardment of native H2O ice and C-rich material on their surfaces. Alternatively comma CO2 ice could be native to these moons and sourced from their interiors comma hinting at recent geologic activity. To investigate whether charged particles modify these four moons. surface compositions comma we will collect UV spectra and conduct a series of measurementsdoublePoint (1) compare the near-UV (300 nm) albedos of each moon.s leading and trailing hemisphere to characterize longitudinal and radial trends in charged particle irradiation (2) measure an absorption band that spans 257 to 360 nm comma attributed to trapped OH formed by charged particle irradiation of H2O ice comma on each moon.s leading and trailing hemisphere to characterize longitudinal and radial trends in the distribution of this feature (3) compare the distribution of the 280-nm trapped OH band to the distribution of CO2 ice (4) compare these new STIS spectra that would be collected over the northern hemispheres of these moons (sub-observer lat. 55 N) to archived HST-FOS spectra that were collected over their southern hemispheres (sub-observer lat. 45 S) to characterize any latitudinal trends in charged particle irradiation that might be present.