Soutenance de thèse d’Erick Meza le vendredi 28 septembre 2018

Titre de la thèse

"Observations d’occultations stellaires, applications à l’étude de la structure et l’évolution de l’atmosphère de Pluton"

Directeur de thèse

Bruno Sicardy (pôle planétologie)

Résumé

The main topic of this 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.

Those occultations probed Pluto’s tenuous nitrogen (N2) atmosphere from a few kilometers above the surface (pressure ∼10 microbar) up to 380 km altitude (∼10 nbar). 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 analysis of those occultations 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.

Mots-clefs

Pluton, atmosphères, stellar occultations, éphémérides