Snapshot from a dynamical simulation after 50 orbital periods

Except for the larger size (corresponds to 8 by 8 Toomre critical
wavelengths), the paramaters are the same as in the 'IDE' model analyzed in
Salo, Karjalainen, French (2004; Icarus 170, 70; see Figs. 2-3, 
also the cover).

 Geometric optical depth tau=0.5
 Saturnocentric distance 130 000 km
 Internal density of particles 450 kg/m^3
 Particle radius 1.667  --> yields surface density 500 kg/m^2
 Particle elasticity follows Bridges et al. (1984) velocity-dependent
                    coefficient of restitution
 Number of particles about 20000