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Our mapping of the wispy terrains on Saturn's moons Dione has revealed unique linear features that are generally long (tens to hundreds of kilometers), narrow (<5 km), and brighter than the surrounding terrains. We refer to these features as linear virgae. Similar features, with a limited distribution, have been observed on Rhea. Wherever linear virgae are observed, they appear to crosscut all other structures suggesting that they are among the youngest features on these satellites. Here we seek to constrain whether the linear virgae are endogenic, suggesting that the surface of Dione has been geologically active recently or if they are exogenic, suggesting a recent, or even ongoing, process in the Saturn system. We favor an exogenic mechanism for the formation of linear virgae on Dione by the emplacement of material across the surface by low-velocity impacts of material sourced from Saturn's rings, co-orbital moons, or encountering planetocentric debris.

Plain Language Summary After the arrival of the Cassini spacecraft to the Saturnian system, unusual linear features were observed across Dione. We also noticed similar features on Saturn's moon Rhea. We name these features linear virgae (virgae meaning a stripe or streak of color) and report on their distribution and characteristics as they are observed on the surfaces of Dione and Rhea. Our understanding of the distribution of linear virgae across Rhea is incomplete, likely because of data coverage; however, on Dione, we find that linear virgae are parallel to the equator and are confined to the region between 45 degrees N and 45 degrees S. We explored different ways of forming linear features on planetary surfaces and favor the draping of exogenic material across a planetary surface by encounters with either Saturn's rings, co-orbital moons, or close flyby of comets. This debris may introduce materials into the Dione system that could contribute to creating a more habitable Dione.