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Observations of stellar occultation : applications to study of the structure and evolution of Pluto’s atmosphere

Abstract : Ground-based stellar occultations are a very efficient method to probe Pluto's tenuous nitrogen (N2) atmosphere from a few kilometers above the surface (pressure ~10 microbar) up to 380km altitude (~10nbar). This atmosphere is strongly coupled with Pluto's surface properties (distribution of ices, thermal inertia and surface temperature), as the gaseous N2 is in vapor pressure equilibrium with the nitrogen ice. This induces strong seasonal effects, due to the large obliquity (~120 deg) and high orbital eccentricity (0.25) that takes the dwarf planet from 30 to 50 au during half of its 248 year orbital period. The main topic of my thesis is an overview of twenty ground-based stellar occultations by the dwarf planet Pluto, that have been organized between 2002 and 2016 by the LESIA occultation group. My analysis of eleven campaigns of occultations with hight S/N ratio has been used to: (1) derive Pluto's atmospheric pressure changes on decadal time scales (1988-2016), and provide constrains on the current seasonal models of the dwarf planet, putting them in perspective with the NASA New Horizons flyby of July 2015; (2) compare our ground-based derived results with the New Horizons findings, and in particular with the results of the radio science (REX) experiment below the altitude ~115 km; (3) use the reconstructed geometries of the occultations and the newly released Gaia DR2 catalog to improve Pluto's orbital elements and provide an new ephemeris for the dwarf planet.
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Erick Gregorio Meza Quispe. Observations of stellar occultation : applications to study of the structure and evolution of Pluto’s atmosphere. Astrophysics [astro-ph]. Sorbonne Université, 2018. English. ⟨NNT : 2018SORUS516⟩. ⟨tel-03001235⟩

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