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Modélisation de la dynamique des fragments cométaires - Application à la comète C/1996 B2 Hyakutake

Abstract : Cometary nuclei are among the most pristine bodies in the Solar System. They are almost impossible to observe directly. The study of the dynamics of the cometary fragments provide an indirect way to characterize them. The aim of this thesis is to contribute to the understanding of this phenomenon. Comet C/1996 B2 Hyakutake passed within 15 million kilometers of the Earth in March 1996. Bright condensations were observed in the near-nucleus coma, in the anti-solar direction. Observations coming from various observatories were gathered and processed in order to obtain the precise temporal evolution of the positions of bright condensations with respect to the nucleus. With the assumption that these condensations were due to icy cometary fragments, a model was developed for the dynamics of these fragments. Three forces were considered: the gravity of the Sun, their mutual gravity, and a non-gravitational force due to the sublimation of the water ice. The positions of the fragments were computed by a direct numerical integration of the relevant forces. An excellent agreement was obtained with the observations of comet Hyakutake, suggesting the existence of seven fragments. The products of their density and their radii are near 10000 kg.m-2. Their separation dates have been correlated to an outburst of the comet. The model was applied to comet 46P/Wirtanen, target of the space mission Rosetta. Trajectories of several thousands of hypothetical fragments were computed, and then statistically processed. It was shown that the probability of presence of a fragment in the coma is not isotropic. Recommendations were deduced in order to reduce the collisional risks.
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Contributor : Emmanuel Desvoivres <>
Submitted on : Wednesday, April 13, 2005 - 5:01:13 PM
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Emmanuel Desvoivres. Modélisation de la dynamique des fragments cométaires - Application à la comète C/1996 B2 Hyakutake. Astrophysique [astro-ph]. Université Joseph-Fourier - Grenoble I, 1999. Français. ⟨tel-00009012⟩

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