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EP: Extraterrestrische Physik

EP 20: Monde, Ringe und kleine Körper

EP 20.1: Invited Talk

Thursday, March 16, 2006, 16:30–17:00, B

Moonlets in Planetary Rings? Implications for an Origin Scenario. — •Frank Spahn — Uni Potsdam

To date it is nor clear whether planetary rings have formed by co-genetic accretion together with their central planet or has a catastrophic disruption of a parent body (satellite, comet) created these magnificent cosmic structures. Based upon dynamical arguments the former scenario would ab initio exclude the existence of boulders larger than 10 meters in diameter because they cannot stand the planet’s tides. On the other hand, if there were such moonlets with sizes between 50 meters up to few kilometers in diameter a strong argument pro the hypothesis of a No-dqviolent birthNo-dq of these cosmic disks would have been found. In order to improve the detectability of such moonlets we investigated and modeled structures created by such larger ring-boulders. We modeled the counteracting processes of gravitational scattering and nonlinear viscous diffusion and obtained a No-dqpropeller-shapedNo-dq structure interfered with density wakes. They scale radially with the Hill radius and in azimuthally with the ratio of mass to ring-viscosity. In order to check the structures predicted by the hydrodynamical model we performed particle simulations to study the density structures in the ring caused by an embedded small moonlet. We verified the formation of the No-dqpropellersNo-dq flanked by density wakes. Kilometer-sized moonlets – Pan and Daphne – have already been detected in Saturn’s A ring by the Cassini cameras which both show all essential density features, and there are good chances to resolve even smaller boulders in Saturn’s rings. Based on these results the catastrophic origin scenario seems to be more likely.