Cassini UVIS FUV Phase Curve Maps and the Age of Saturn’s Rings as a Function of Radius

We present the FUV phase curves of Saturn’s rings as a function of radius relative to the center of the planet, for both the lit and unlit side of the rings. This updated analysis expands on our previous work (Elliott and Esposito 2021, DPS) by examining the phase curves of the rings at a finer granularity. Each of the examined ring regions, A, B and C, are broken down into smaller annuli to illustrate the variability of the phase curves as a function of radius. Particularly in the B ring, which has several distinct regions with varying optical depth and particle size distributions (Colwell et al. 2018), characterization of the radial dependence of the phase curves can be important in the compositional analysis of the rings. Next, we use the phase dependence of the FUV reflectance at each ring annulus to derive the macroscopic roughness of the rings, which is important to understand because it represents the degree of surface shadowing that occurs which can reduce the effective brightness of rings. This darkening of the rings due to shadowing can be misinterpreted as a pollutant material mixed in with the icy regolith and therefore is important to quantify.

By constraining the macroscopic roughness, or surface shadowing, we reduce it to a fixed parameter in our least-squares best-fit Hapke model for the fractional pollution of the Saturn’s rings. Obtaining the current state of the fractional pollution of the rings, we then run our Markov-chain based model for meteoritic bombardment of the rings (Elliott and Esposito 2011) backward in time to estimate the age of Saturn’s rings.