Modélisation dynamique et spectroscopique des astéroïdes: applications aux géocroiseurs et aux cibles de missions spatiales

Abstract : The studies of the minor bodies are crucial in the understanding of the formation and evolution of our Solar System. As the only remnants of the early stages of planetary history they recorded the complex chemical and physical evolution that occured in the solar nebula. Recovering this record requires the knowledge of both dynamical and physical properties of the current minor bodies population. In this framework I have addressed the astrometry of the Near Earth Asteroids (NEA) by proposing a new method of obtaining their positions directly in the International Celestial Reference Frame (ICRF). I have constructed 8 years (2010 - 2018) ephemerides for a set of 836 numbered NEA using a Bulirsch-Stoer numerical integrator. I have then searched for apparent close approaches between NEA and quasars (as quasi-inertial, fiducial points) from Large Quasar Astrometric Catalog (LQAC). I have found a large number of close encounters that could provide by differential astrometry positions of NEAs with an accuracy better than that of the current observations method. This set of optical data together with radar observations can be used in constraining NEA dynamics and possibly revealing more subtle, non-gravitational phenomena as the Yarkovsky effect. This large number of events could also be used as an observational basis to derive the link between de Dynamical Reference Frame realised by the ephemerides of NEAs and ICRF. In preparation of the ESA’s space mission Rosetta I have investigated two of its targets : the asteroids (21) Lutetia and (2867) Steins. Using in remote mode the NASA Infrared Telescope Facility (IRTF) located in Mauna Kea, Hawaii I have obtained near-infrared spectra (0,8 – 2,5 microns) of these two objects. The spectra of (21) Lutetia pointed to a primitive, chondritic composition. The rotational resolved spectroscopy of the surface revealed a spectral variation that is corellated with the rotational phase. This variation that was later confirmed by other investigations was interpreted in terms of the coexistence of several lithologies on the surface. The spectroscopy of (2867) Steins confirmed its taxonomic classification as an E-type asteroid and its belonging to a sub-class of this type that has no spectral analog among the known meteorites. For both asteroids i have performed a mineralogical analysis using laboratory spectra from databases of known minerals and meteoritic materials. In the framework of this PhD thesis I have participated in observational programmes dedicated to the astrometry of NEA and of the optical counterparts of ICRF defining objects - the quasars. I have also obtained near-infrared spectra of asteroids designated as targets of the space missions. I have reduced, analyzed and interpreted the data acquired during these programmes of studying the physical and dynamical properties of asteroids.
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Dan Alin Nedelcu. Modélisation dynamique et spectroscopique des astéroïdes: applications aux géocroiseurs et aux cibles de missions spatiales. Astrophysique [astro-ph]. Observatoire de Paris, 2010. Français. ⟨tel-01958541⟩

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