Surface modification of icy satellites: Space weathering of the large moons of Uranus and alluvial fan formation on Saturn’s moon Titan

The surfaces of icy satellites are continually modified by space weathering and geologic processes. This dissertation explores the processes changing the surface compositions of the large moons of Uranus and mechanisms for development of possible alluvial fans on the Saturnian moon, Titan. On the Uranian satellites, I hypothesize that the origin and distribution of carbon dioxide ice results from charged particle bombardment, and that spectrally red material originated on retrograde irregular satellites. On Titan, I hypothesize that landforms identified as alluvial fans at low and mid latitudes were formed by sheetfloods, whereas possible alluvial fans at high latitudes were formed by debris flows.

To test whether charged particle radiolysis drives carbon dioxide ice synthesis on the classical Uranian moons, I gathered new near-infrared (NIR) reflectance spectra over a range of satellite longitudes, and measured the areas of carbon dioxide ice bands in these data to constrain its distribution on their surfaces. I found that the abundance of carbon dioxide ice peaks on the trailing hemispheres of the moons closer to Uranus (Ariel and Umbriel), consistent with radiolytic production of carbon dioxide ice via magnetospherically-embedded charged particle bombardment. Using these same NIR spectra, I measured the spectral slopes and areas of water ice bands to constrain the distribution of red material on these moons. My water ice band area and spectral slope measurements indicate that red material is most abundant on the leading hemispheres of the outer moons, Titania and Oberon, consistent with delivery of red dust from the irregular moons.

To test alluvial fan formation mechanisms on Titan, I measured the radar backscatter of possible alluvial fans located at different latitudes on Titan, and compared these backscatter measurements to alluvial fans formed by sheetfloods and debris flows on Earth. My results indicate that backscatter from possible fans at high latitudes on Titan is more consistent with sheetflood fans on Earth, and backscatter from low- and mid- latitude possible fans on Titan is more consistent with terrestrial debris flow fans. I explore the geomorphic and sedimentological implications of these results.