Macroscopic Roughness, Composition and Age of Saturns Rings and FUV Phase Curve Analysis

Macroscopic roughness of an objects surface can affect its observed reflectance. This is an important parameter to constrain when attempting to characterize the mixing ratios of constituent materials on the surface of the object because the darkening due to surface shadowing can mimic a more polluted smooth surface. In the case of Saturns ring particles, macroscopic shadowing can have a large effect in this regard. FUV (far ultraviolet) phase curves of Saturn's rings, derived from Cassini UVIS (Ultraviolet Imaging Spectrograph) observations collected over a range of viewing geometries, are used to constrain the macroscopic surface roughness parameter in our Hapke based reflectance model. This constraint allows us to reduce the number of free parameters of our model, which allows us to more precisely determine the fractional abundance of the constituent materials on the surfaces of the ring particles. Given a set of candidate end-member spectra as inputs to our least-squares best-fit Hapke model we calculate the fractional pollution of the rings. Using this result, we then utilize our Markov-chain based model for the bombardment of the rings over time to estimate the age of Saturns rings.