Stochastic forces in circumplanetary dust dynamics

Details Stochastic forces in circumplanetary dust dynamics Stochastic forces in circumplanetary dust dynamics

Apr 2003

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003jgre..108.5021s&link_type=abstract

Journal of Geophysical Research (Planets), Volume 108, Issue E4, pp. 2-1, CiteID 5021, DOI 10.1029/2002JE001925

Physics

Geophysics

4

Planetology: Solar System Objects: Dust, Planetology: Solar System Objects: Planetary Rings, Magnetospheric Physics: Planetary Magnetospheres (5443, 5737, 6030), Mathematical Geophysics: Nonlinear Dynamics

Scientific paper

Charged dust grains in circumplanetary environments experience, beyond various deterministic forces, also stochastic perturbations caused, by fluctuations of the magnetic field, the charge of the grains, by chaotic rotation of aspherical grains, etc. Here we investigate the dynamics of a dust population in a circular orbit around a planet which is perturbed by a stochastic planetary magnetic field B', modeled by an isotropically Gaussian white noise. The resulting perturbation equations give rise to a modified diffusion of the inclinations i and eccentricities e: <Δx2> ~ D Δt (here x = e or i, t is time). The diffusion coefficient is found to be D ~ ωG2 |Δn|/n2, where the gyrofrequency, the Kepler frequency, and the synodic frequency are denoted by ωG, n, and Δn, respectively. This behavior has been checked against numerical simulations. We have chosen dust grains (1μm in radius) ejected from Jupiter's satellite Europa in circular equatorial orbits around Jupiter and integrated numerically their trajectories over their typical lifetimes (100 years). The particles were exposed to a Gaussian fluctuating magnetic field B' with the same statistical properties as in the analytical treatment. These simulations have confirmed the analytical results. The theoretical studies showed the statistical properties of B' to be of decisive importance. To estimate them, we analyzed the magnetic field data obtained by the Galileo spacecraft magnetometer at Jupiter and found almost Gaussian fluctuations of about 5% of the mean field and exponentially decaying correlations. This results in a diffusion of orbital inclinations and eccentricities of the dust grains of about ten percent over the lifetime of the particles. For smaller dusty motes or for close-in particles (e.g., in Jovian gossamer rings) stochastics might well dominate the dynamics.

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