DDA 36th Meeting, 10-14 April 2005
Session 11 Orbits and Orbit Evolution II: Moons

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[11.06] Dynamics of Neptune's Small Satellites

K. Zhang, D. Hamilton (University of Maryland)

The capture of Triton probably forced an early population of Neptunian satellites onto chaotic paths leading to mutual collisions and self-destruction. The current small inner satellites then reformed out of the resulting debris disk during or after Triton's orbit was tidally circularized. With massive Triton on a nearby tilted retrograde orbit, this new generation of satellites experienced a unique formation and evolution history. The study of their dynamical past can provide information about the capture of Triton, and constrain the physical properties of the planet and the satellites.

Observations of the inner satellites show that they all have small, but non-zero inclinations relative to their local Laplacian planes. If we assume that they formed with zero inclinations from an extremely thin disk (like Saturn's rings), then the tilts of their current orbits, albeit small, require an explanation. We are investigating the hypothesis that passages through inclination-type mean motion resonances are responsible.

We have carried out numerous numerical simulations on the 4:2 and 5:3 resonances between Proteus and Larissa. Our results show that, without Triton, these second-order inclination resonances are by far too weak to match the observations. With Triton in the system, however, we find that, for each passage, the three second-order inclination resonances are dominated by two new stronger ones. We have identified the newcomers as 3-body resonances involving the nodal precession of Triton. Their high strength is due to Triton's huge mass and large orbital tilt. Our preliminary findings indicate that three or four resonant passages (e.g. Proteus 6:4, 5:3, 4:2) are enough to kick the inclination of Larissa to its current value. In this case, Proteus must have formed interior to about 4RN rather than at its current location (a=4.67RN).

Finally, the 4.7\circ tilt of the innermost satellite Naiad has been interpreted as the result of a capture into a second-order mean motion resonance (Banfield and Murray 1989). The presence of many much stronger 3-body resonances in the region will modify this picture somewhat. We are working on the details.

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 #2
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