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Etude des interactions anneaux-satellites

François Poulet 1
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IRISA - Institut de Recherche en Informatique et Systèmes Aléatoires, Inria Rennes – Bretagne Atlantique
Abstract : The physical and dynamical properties of Saturn’s inner satellites and rings are studied from new observations obtained during the Earth and Sun ring plane crossings in 1995. In those particular circumstances, several goals have been achieved. The optical properties of four inner satellites (Prometheus, Pandora, Epimetheus, Janus) and five rings (the four main rings and the F ring) have been determined from 0.3 to 0.9 µm. The spectrophotometric study (albedo and color) has indicated strong correlations between these objects, which provides some constrains on their origin. The photometric profiles of edge-on rings allowed to study their vertical structure. The residual flux is dominated by the F ring. A photometric modelling gives a physical thickness of the F ring of 21 ± 4 km. Such a vertical distribution is consistent with the interactions between ring particles and shepherding satellites and/or with gravitational stirring by large bodies of a few km radius. This period of observations turned to account to discover new ring features lying near the F ring. Our observations combined with other data show that these new objects are likely to be transient with lifetime inferior to several months. A scenario to explain their formation and destruction is proposed : each objects is a regolith cloud resulting from a collision between two parent bodies. The characteristics of the parent bodies population are derived from an analytical model in which the processes of collision and accretion are included. In addition to the results directly stemming from ring plane crossing observations, I modeled the dynamical evolution of the inner satellites. Two complementary approaches (analytical and numerical) show that the converging orbits of Prometheus and Pandora should end up to a close encounter in less than 20 millions of years. The primary mean motion resonances between the two satellites play the role of protection mechanism against the convergence, which increases, the dynamical lifetime of the satellites couple by several tens millions of years. The implications of this evolution on the rings origin are discussed.
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François Poulet. Etude des interactions anneaux-satellites. Astrophysique [astro-ph]. Observatoire de Paris, 1998. Français. ⟨tel-01958567⟩