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Étude dynamique des systèmes multiples de petits corps : application au système de Pluton

Abstract : A multiple system refers to a set of small bodies tied by gravitation and orbiting around their common center of mass, which orbits around the Sun. Astrometric observations of those systems grant us access to parameters which would be harder to determine through other methods, more speci fically the masses of the system's componants. In order to deduce the value of those parameters from astrometric observations of those objects, we have created an N-bodies numerical model. Our model includes the integration of orbital motion's variationnal equations, a key feature for least-square method fitting. We applied our model to Pluto's system, the multiple system with the longest observationnal timespan. Pluto's sytem possesses features of both classical planetary system and multiple system. Indeed, Pluto is in hydrostatic equilibrium and its smallest satellites have a negligible mass compared to its, a trait which is shared by planetary systems. But its most massive satellite, Charon, is massive enough to consider Pluto/Charon to be a binary object. In order to reproduce both the heliocentric motion of Pluto, disturbed by the influence of its satellites, and the motion of said satellites, we have integrated the equations of motions in a reference frame centered on the Solar System barycenter. We have included the perturbations from the planets and the second order polar oblateness of Pluto and Charon. The obtained model is then tted to observations or simulated data thanks to least-square method. First, we have fi tted our model to simulated data in order to study the evolution of the uncertainty on Nix's and Hydra's mass. We show that their mass will most probably remain unconstrained until the arrival of New Horizons probe in the system. We also show that the effect of the polar oblateness on the orbits is negligible considering the uncertainty of the observations. We used this method to determine the future contribution of GAIA to our knowledge of the system. Then, we have fitted our model to astrometric observations of the system. The fitting of the model to the observations has given post- fit residuals close to those of previous studies while giving very di fferent masses for Nix and Hydra. Nonetheless, both in our study and the previous ones, the said masses are unconstrained enough for the results to remain coherent. The solution for the satellites' motion we then obtained has been used during our fitting of Pluto's heliocentric motion, in order to reproduce as accurately as possible Pluto's motion around its system barycenter. At last, we have adapted our model to (45)Eugenia's system and have found results compatible with previous studies. As our results are based on a larger timespan than before, with new observations, our modelization of the satellites' motion should remain accurate on a longer timespan.
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Contributor : Laurène Beauvalet <>
Submitted on : Thursday, April 19, 2012 - 4:14:46 PM
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  • HAL Id : tel-00689508, version 1

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Laurène Beauvalet. Étude dynamique des systèmes multiples de petits corps : application au système de Pluton. Planétologie et astrophysique de la terre [astro-ph.EP]. Observatoire de Paris, 2011. Français. ⟨tel-00689508⟩

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