Study of Titan in the near infrared by means of spectro-imagery coupled with adaptative optics

• Main Author: Hirtzig, Mathieu
• Other Authors: Laboratoire d'études spatiales et d'instrumentation en astrophysique = Laboratory of Space Studies and Instrumentation in Astrophysics (LESIA), Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Université Paris Cité (UPCité), Paris 11, Athéna Coustenis
• Format: Doctoral or Postdoctoral Thesis
• Language: French
• Published: HAL CCSD 2005
• Subjects: Planetology Satellite; Planétologie Satellite; [PHYS]Physics [physics]; [PHYS.ASTR]Physics [physics]/Astrophysics [astro-ph]; Ice; permafrost
• Online Access: https://hal.science/tel-03523497; https://hal.science/tel-03523497/document; https://hal.science/tel-03523497/file/these_Hirtzig.pdf

Titan, Saturn's main satellite, is still a mysterious object, despite the arrival of Cassini/Huygens. Yet we can rely on Adaptive Optics: my work presented herein is based on the 1998-2005 infrared data acquired with imagery (PUEO/CFHT, NACO/VLT), spectroscopy (NACO) or Integral Field Spectrometry (OASIS/WHT). In the 0. 8-2. 0µm spectral range, both the atmosphere and the surface of Titan can be probed down to, in or out of five methane windows. Voyager revealed the asymmetry splitting Titan's atmosphere in two, North and South, because of a local enhancement of aerosols in the winter hemisphere. We could monitor the inversion of this asymmetry, when Titan entered into Southern summer : since 2002, the Northern limb is the brightest. We also describe other subtle features, such as the condensation of aerosols at 80km of altitude during Titan's night; or the complex meteorological system, confined within the 70th parallel, between 18 and 83km, probably made of small deforming clouds, but we still ignore their true nature or origin. We studied Titan's surface by constructing maps at 1. 28, 1. 6 and 2. 0µm, with a stunning similarity to HST or Cassini ones. We also tried to identify the chemical composition of the bright and dark features by means of differential spectroscopy water ice is a good candidate as the main constituent of the surface, with either an excess of bright methane/ethane ices, or an excess of dark hydrocarbon liquids. We do not detect any specular reflection, ruling out the existence of large bodies of liquid on the surface : how about a permafrost of liquid ethane within solid water ice as the replenishing source of the atmospheric methane Malgré l'arrivée de Cassini/Huygens dans le système Saturnien, Titan reste encore bien mystérieux. C'est là que peut intervenir l'Optique Adaptative: les travaux présentés ici reposent sur l'étude des données 1998-2005 acquises en infrarouge proche, par imagerie (PUEO/CFHT, NACO/VLT), spectroscopie (NACO) et spectroscopie à intégrale de champ (OASIS/WHT). ...