Dust in the arcs of Methone and Anthe

Methone and Anthe are two tiny moons (with diameter < 3 km) in the inner part of Saturn's E ring. Both moons are embedded in arcs of dust particles. To understand the amount of micron-sized dust in these arcs and their spatial distributions, we model the source, dynamical evolution, and sinks of the dust in the arc. We assume hypervelocity impacts of micrometeoroids on the moons produces these dust (Hedman et al., 2009), via the so called impact-ejecta process (Krivov et al., 2003; Spahn et al., 2006). After ejecting and escaping from the moons, these micron-sized particles are subject to several perturbing forces, including gravitational perturbation from Mimas, oblateness of Saturn, Lorentz force, solar radiation pressure, and plasma drag. Particles can be either confined in the arcs due to corotational resonance with Mimas, like their source moons (Cooper et al., 2008; El Moutamid et al., 2014; Hedman et al., 2009; Spitale et al., 2006), or pushed outward by plasma drag. Particle sinks are recollisions with the source moon, collisions with other moons, or migration out of the zone of interest. The erosion of particles due to plasma sputtering is also considered (Johnson et al., 2008), although its timescale is much larger than other sinks. Our simulation results show that ejecta from both moons can form maximal number densities between 10(-4) and 10(-3) m(-3). In comparison with the observations of Anthe arc, the peal< value in simulations is about an order of magnitude smaller. Plausible explanations for the difference include millimeter-sized particles as additional source and the uncertainties of impactor flux F-imp and the yields Y. The longitudinal extension of the Methone/Anthe arc in our simulation is 10.8 degrees /15 degrees, consistent with observations and theory (Hedman et al., 2009). Our results also show the lifetime distributions of particles and the heliotropic behavior of dust introduced by solar radiation pressure (Hedman et al., 2010a). The lifetimes of arc particles, defined by the time particles stay in the semi-major axes close to the source moons, are also related to particle size. Smaller ones (< 5 mu m) do not stay in the arc and instead migrate outward under the influence of plasma drag. Larger grains can stay in arc in the timescale of 100 years until they leave the arcs or collide with the source moons. (C) 2016 Elsevier Inc. All rights reserved.