DPS 35th Meeting, 1-6 September 2003
Session 4. Other Planetary Satellites I
Oral, Chairs: L. Bruesch and M. L. Delitsky, Tuesday, September 2, 2003, 1:30-3:00pm, DeAnza III

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[4.09] Are Irregular Satellite Systems Shaped by Secular Resonances?

M. Cuk, J. A. Burns, V. Carruba (Cornell U.)

In order to explore how the irregular satellites are distributed through the orbital phase space criss-crossed by secular resonances, we numericaly surveyed secular behavior for a wide range of semimajor axes, eccentricities and inclinations i. We observed that the minimum inclination for Kozai resonance is not uniformly 39.2\circ (Innanen et al. 1997) but instead depends significantly on mean motion n. We found the critical inclination icrit to be lower (closer to the reference plane) for distant retrograde satellites but higher for prograde ones. We corrected Innanen et al.'s formulae for {\dot \omega} and {\dot \Omega} by incorporating terms (Saha and Tremaine 1993) of third and higher orders in n to {\dot \varpi}. Thus corrected, the new icrit agrees with both our numerical survey and simulations of observed satellites.

The irregular satellite orbits seem to be grouped about this modified icrit in a-i space. This clustering includes all objects in secular resonance, since pericenters lock at inclinations a few degrees below icrit. Also, all known Kozai resonators are found no more than a few degrees above this boundary. Since the largest irregular satellites are all distant from this complex, perhaps there is some fundamental dichotomy in the origins of irregulars of different sizes.

In the course of our phase-space survey, we identified a new secular resonance that strongly affects eccentricity and that even induces orbits to become unstable. It occurs when the precession period of satellite's \varpi enters a 2:1 commensurability with the Great Inequality of Jupiter and Saturn. While no satellites are present today near this resonance, it may have affected some of the extant objects during the epoch of planetary migration, when the Great Inequality swept through a large range of frequencies.

The author(s) of this abstract have provided an email address for comments about the abstract: cuk@astro.cornell.edu

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Bulletin of the American Astronomical Society, 35 #4
© 2003. The American Astronomical Soceity.