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K. Zhang, D. P. Hamilton (University of Maryland)
Observations show that all of Neptune's inner satellites have small but non-zero inclinations relative to their local Laplacian planes. If we make the reasonable assumption that the moons formed from an extremely thin accretion disk (similar to Saturn's rings) resulting from catastrophic disruption of the original satellite system during the capture of Triton, then the orbital tilts of the moons, albeit small, require an explanation. We are investigating the hypothesis that passages through inclination-type mean motion resonances during satellite migration are responsible for these inclinations. With massive Triton on a nearby tilted orbit, this process can be significantly different from those that happened elsewhere in the Solar System. Furthermore, the study of the dynamical history of the system can help establish Triton's capture scenario and constrain the physical properties of both the planet and the satellites.
Through detailed numerical simulations for a series of first- and second-order mean motion resonance encounters between Proteus and Larissa, we find that, for each resonance passage, the three second-order inclination resonances, which usually provide the strongest inclination kicks, are dominated by two new ones. We have identified the newcomers as 3-body resonances involving the nodal precession of Triton. Our findings indicate that the two satellites probably need to pass through at least three mean motion resonances (2:1, 5:3 and 3:2) to account for their current orbital tilts, which requires that Proteus have formed interior to 4.25RN rather that at its current location of 4.7RN, and Neptune's Q is less than 24000. It is not clear whether additional resonances occurred due to chaotic evolution resulting from the overlap of strong first-order eccentricity resonances which happened for resonances that may have occurred earlier than the 5:3. These chaotic interactions can strongly affect satellite inclinations.
Finally, the 4.7\circ tilt of the innermost satellite Naiad has been interpreted as the result of capture into a second-order mean motion resonance (Banfield and Murray 1989). The presence of many much stronger 3-body resonant encounters in the region will modify this picture significantly.
The author(s) of this abstract have provided an email address for comments about the abstract: kzh@astro.umd.edu
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Bulletin of the American Astronomical Society, 37 #3
© 2004. The American Astronomical Soceity.