THEORY OF THE NEPTUNIAN ARCS - A MULTICOMPONENT EPITON AND GALATEA

The effect of Galatea on epitons, stable local particle clusters in th e Neptunian arcs, has been investigated numerically. The model allows for the mutual accretion of inelastic particles and the tidal disrupti on of the largest of them. It is shown that Galatea causes periodic va riations in an epiton's eccentricity, the number of particles, and the ir frequency of collision. The relative dispersion in the semimajor ax es of the particle orbits for an epiton reaches 2 . 10(-6), which corr esponds to a collision velocity of 2 cm/sec. An epiton remains stable if the probability for particle adhesion during collisions is close to unity. The typical diameter of an epiton's largest particles is estim ated to be several hundred meters. An individual epiton may consist of 15 to 20 such particles in all. The epitons in the Neptunian arcs are in a stable 42:43 Lindblad resonance with Galatea if the eccentricity of its orbit e > 5 . 10(-4). Depending on the eccentricity and mass o f Galatea, an epiton librates with a period of 230 to 480 revolutions and with an amplitude from 0.2-degrees to 0.3-degrees.