Simulations of Moonlets in the A Ring

 

This page links to movies of simulations of moonlets embedded in Saturn's rings, particularly the A ring. Significant work has been done on simulating embedded moonlets by Frank Spahn and his collaborators. This work adds to that by adding full particle self-gravity to the smulations. Spahn's group has typically included a forcing toward the midplane to mimic some of the impact of particle self-gravity, but that doesn't produce the clumping effects of gravity wakes (Toomre instabilities). This work also investigates the impact of having broad size distributions of particles on the formation of so called "propellers" adjacent to the moonlets.

Sim Name N Moonlet Size (m) Particle Diameter (m) Optical Depth Particle Density (g/cm^3) Surface Density (g/cm^2) Partice Animation Orbit Properties Animation
L1 795,713 260 10.4 0.1 0.5 36.1 grav/no grav grav/no grav
L2 127,312 260 26 0.1 0.5 88.5 grav/no grav grav/no grav
L3 353,652 260 15.6 0.1 0.5 53.4 grav/no grav grav/no grav
L4 353,659 232 15.6 0.1 0.7 74.7 grav grav
L5 353,661 214 15.6 0.1 0.9 96.1 grav grav
S1 759,713 26 1.04 0.1 0.7 4.97 grav/no grav grav/no grav
S2 127,312 26 2.6 0.1 0.7 12.3 grav/no grav grav/no grav
S3 254,624 26 2.6 0.2 0.7 24.6 grav/no grav grav/no grav
D1 389,987 26 q=2.8, 0.52-13 0.1 0.7 21.1 grav/no grav grav/no grav
D2 781,820 26 q=2.8, 0.52-13 0.2 0.7 42.2 grav/no grav grav/no grav
D3 487,535 26 q=2.8, 0.52-3.9 0.1 0.7 14.1 grav/no grav grav/no grav
D4 974,886 26 q=2.8, 0.52-3.9 0.2 0.7 28.6 grav/no grav grav/no grav
D5 1,445,059 26 q=2.8, 0.26-3.9 0.2 0.7   grav/no grav grav/no grav

This animation shows what simulation D4 without self-gravity might look like at low resolution in a backlit situation. The colors are given simply by the geometric optical depth of the particles in each of the bins. Also shown in a weighted average of the particle sizes in each bin. White would correspond to an average radius of 0 while black is an average diameter of 2 meters or larger. While the particle sizes are noisy, it should be noted that the lobes of the propeller consistently have smaller particles than the other parts of the simulation cell. The average particle size is calculated with each particle weighted by its cross-sectional area. Without this weighting, the shear number of smaller particles in every cell swamps the smaller number of larger particles.


Original paper figures with larger scale

Figure 1 - From ciclops.org

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