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B. Sicardy, S. Renner (Observatoire de Paris, LESIA)
Recent HST and Earth-based observations (Dumas, C. et al., Nature, 400, 733, 1999; Sicardy, B. et al., Nature 400, 731, 1999) indicate that Neptune's ring arcs are near but not within the 42:43 corotation resonance with Galatea, thought to be responsible for the azimuthal confinement of the arc system (Porco, C.C., Science, 253, 995, 1991).
Consequently a new resonance structure based only on Galatea's eccentricity has been proposed to explain the arcs' stability : if the arcs have a sufficient fraction of the mass of Galatea, then the 42:43 eccentric corotation resonance with this moon, located in the massless case ~ 3 km inside the arcs' orbit, can match the current arcs' semimajor axis (Namouni, F. and Porco, C.C., Nature, 417, 47, 2002). The ring mass they determined corresponds to a parent ~ 10-km-radius satellite with a density similar to that of Galatea. Because Voyager data exclude undetected satellites of radius larger than ~ 6 km, the mass required for the arcs' confinement is probably not contained in a single body.
Here we present an alternative solution fully compatible with the latest observations in which small co-orbital satellites confine the observed dusty ring material. These hypothetical co-orbital bodies would be in a stable stationary configuration. There is an infinity of solutions for such stationary configurations, depending on the satellite masses (Renner, S. and Sicardy, B., CeMDA, submitted), which reproduce all the features of the arc system. We have tested numerically the stability of the system over centuries, in a purely gravitational case but also under the effects of collisions and PR drag. We show how Adam's ring material can evolve towards stable stationary configurations of several co-orbital satellites through the Galatea's secular torques.
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Bulletin of the American Astronomical Society, 35 #4
© 2003. The American Astronomical Soceity.