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V. Carruba, J. A. Burns, P. D. Nicholson, M. Cuk (Cornell University), R. A. Jacobson (JPL)
Irregular satellites are moons that occupy large orbits of significant eccentricity e and/or inclination I around all the giant planets. The irregulars often extend close to the orbital stability limit, about 1/3-1/2 of the way to the edge of their planet's Hill sphere. Secular (Kozai) perturbations allow two kinds of high inclination (I >39.2o) orbits: circulating and librating. In circulating orbits, the argument of pericenter sweeps through all possible values (0-360o). In contrast, for libration, it oscillates around 90o (or 270o).
Objects in a librating state are said to be trapped in the Kozai resonance. Particles on librating orbits undergo more confined eccentricity oscillations than circulating ones with the same value of angular momentum. Hence their orbits do not extend as far from the planet, nor approach it so closely. We surmise that this will increase their long-term stability.
In this work we developed a semi-analytical model to describe the Kozai perturbations and we carried out long-term simulations of hypothetical satellites with SWIFT-WHM, to determine a zone of effective stability around Jupiter and Saturn. The integrations include perturbations from the Sun and all other outer planets, and have been run for up to 1 Byr. We also performed simulations with all the irregular satellites of Jupiter and Saturn.
Our simulations suggest that two of the recently discovered Saturnian moons, S/2000S5 and S/2000S6, could currently be in the Kozai resonance.
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Bulletin of the American Astronomical Society, 34, #3< br> © 2002. The American Astronomical Soceity.