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The moons of Uranus have only been visited once by Voyager 2 during its 1986 flyby. Earth-based telescopic observations show a spectral signature of carbon dioxide ice on the Uranian moons Ariel, Umbriel, Titania, and Oberon, with a somewhat higher abundance on their trailing hemispheres. The inner major moon Ariel exhibits the strongest carbon dioxide ice absorption bands, which then decrease in strength with increasing orbital distance from Uranus, with the outer major moon Oberon exhibiting the weakest absorption bands. Previous work has suggested that these hemispherical and radial trends result from radiolytic production of carbon dioxide ice from interactions between the moons' surfaces and charged particles trapped in Uranus' magnetosphere. Here, we use volatile transport modeling to characterize a possible migration cycle of carbon dioxide on Ariel. We find that carbon dioxide is readily mobilized toward Ariel's equator, and that existing topography such as canyons are locations of favorable deposition for carbon dioxide ice. We predict the presence of carbon dioxide ice deposits on the floors of Ariel's canyons. Our work suggests two possible classes of sources of carbon dioxide: an active source, which may be consistent with either radiolytic production from Uranus' magnetosphere or outgassing from Ariel's interior, or an ancient source that produced CO2 that still exists in stable canyon deposits. A future Uranus orbiter could determine which hypothesis is most likely, or if carbon dioxide could be found both in the form of ice deposits on the surface and in a global exosphere. Uranus' moons have only been visited once by the Voyager 2 spacecraft in 1986. Observations from telescopes on Earth show that there is carbon dioxide ice on four of the five largest Uranian moons, but it is mostly concentrated on one hemisphere. Previous work hypothesizes that this carbon dioxide ice could be made by the moons' surfaces interacting with electrons and ions trapped in Uranus' magnetic field. We tested that hypothesis using a model for Ariel, the moon with the strongest evidence for carbon dioxide ice. We find that carbon dioxide ice will move quickly away from Ariel's poles and toward the equator. Because carbon dioxide moves quickly, our results suggest that carbon dioxide could either be actively produced or uncovered on the surface or could be anciently formed from material coming from Ariel's interior; or both mechanisms could source the carbon dioxide. We also find that carbon dioxide ice deposits are likely on the floors of the canyons that were visible in Voyager 2 images of Ariel's surface. The Uranian moons show a spectral signature of carbon dioxide ice (Ariel most strongly) preferentially on their trailing hemispheres We find that carbon dioxide ice is transported toward Ariel's equator, and both an active and ancient source of carbon dioxide is plausible We predict carbon dioxide deposits on the floors of Ariel's canyons, which could be detected by a future Uranus orbiter

来源平台：JOURNAL OF GEOPHYSICAL RESEARCH-PLANETS