CIRCUMPLANETARY DUST DYNAMICS - EFFECTS OF SOLAR GRAVITY, RADIATION PRESSURE, PLANETARY OBLATENESS, AND ELECTROMAGNETISM

We consider the motions of circumplanetary objects perturbed simultane ously by solar gravity, radiation pressure, planetary oblateness, and electromagnetic forces. Confining ourselves to the planar case, but re taining all nonlinear terms in the eccentricity, we rewrite the orbit- averaged equations for the sum of the four perturbations as a semicano nical system. We derive a conserved integral of the motion which is va lid for initially elliptic orbits of arbitrary size and shape. This in tegral is used to investigate the phase space qualitatively and to sho w how the eccentricity and apses line evolve for various strengths of the perturbation forces. We find several different classes of motion a nd show that near certain critical initial conditions, small variation s in parameters such as particle size or initial semimajor axis can ca use dramatic changes in a particle's orbit. This effect is important i n Saturn's E ring and for Phobos dust. We apply our model to dusty eje cta launched from several moons-Phobos, Deimos, Elara, and Enceladus- and to the motions of Elara itself. In each case, we compare our analy tic results to numerical integrations of the full Newtonian equations of motion. (C) 1996 Academic Press,Inc.