The size distribution of Saturn ring particles using N-body simulations

Abstract:

Determining the nature of the individual constituents of Saturn’s main rings is one of the science goals of the Cassini mission. However, after many studies on Saturn’s main rings, there is still no clear big picture about how the ring individual constituents relate to each other. On the one hand, since the 80's, the modeling of near-infrared spectra has indicated the presence of small, micron-sized constituents, referred to as ‘grains’. On the other hand, Voyager and further missions have probed larger rocks (with a power law size distribution ranging from 0.1 to 10 meters) that have been called ‘particles’. The standard model of Saturn’s main rings constituents is that the ‘grains’ form a regolith covering those ‘particles’. However, this standard model has not been completely validated yet. Specifically, it is put to question by the existence of free grains in the B ring (responsible for the spokes), and indications that the some of biggest grains are larger than the smallest particles (Morishima et al., 2013, Icarus, 221, 888–899). Our recent study (Déau, 2014 Icarus, In press) has hypothesized that grains and particles belong to a single continuous set, characterized by a fractal size distribution. This new hypothesis reconciles de facto the two cited outliers of the standard model with the previous size distributions. The objective of our work is to conduct an in-depth investigation of this new hypothesis. We use N-body simulations using a fractal size distribution and a power law distribution, and we compare the results of these simulations with very specific Cassini observations. We will present the results of these comparisons and show how they affect our understanding of the size distribution of the ring particles.