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M. Cuk, J. A. Burns, V. Carruba, P. D. Nicholson (Cornell U.), R. A. Jacobson (JPL)
We report that some of the recently found irregular satellites of Saturn, and possibly Uranus, dwell in hitherto unobserved resonances. These include the Kozai resonance, previously postulated but never before found in our Solar System. We also describe a new type of secular resonance for irregular satellites at higher inclinations (40-45\circ ), which locks the satellite's pericenter with that of the planet.
Comparing theoretical predictions (Carruba et al. 2002)with the orbits of those Saturnian irregulars having inclinations around 45\circ , we found that Saturn's 2000_S5 and 2000_S6 have extremely slow motions of their arguments of pericenter, and their pericenters are presently almost 90 degrees away from their nodes (Jacobson 2001).
Longitude of pericenter of another prograde satellite of Saturn, 2000_S3, precesses extremely slowly (Jacobson 2001). We simulated the motion of a clone of 2000_S3 and found that its longitude of pericenter could be librating around that of Saturn, with a very long period (on the order of 30,000 years) and large amplitude (120\circ ). The nature of this resonance appears different from one affecting certain Jovian moons (Saha and Tremaine 1993).
If the amplitude of pericenter librations can be that large, another Saturnian irregular, 2000_S2, could be in a similar resonance. The Uranian retrograde satellites Stephano and Caliban (at inclinations of about 140\circ ) also have \varpi's that precess very slowly and are roughly aligned with Uranus's (Jacobson 2000). We are currently examining their motion to see if they are also in a resonance similar to that seen at 2000_S3.
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, 34, #3
© 2002. The American Astronomical Society.