New windows into the atmospheric and orbital properties of exoplanet systems
Intervenant : Vincent Bourrier
Université de Genève
Close-in exoplanets represent a large fraction of the known population, and evolve in conditions unknown in the solar system. Atmospheres offer insight into the physical and chemical properties of these faraway worlds, and can be probed during the transit of their host star. Close-in planets are well suited for such observations, because their atmosphere heated and swollen by the star yields deeper transit signatures. The largest signals are retrieved from the outer atmospheric layers: they can become so extended that they lose massive amounts of gas, forming exospheres much larger than the planets. In the first part of this seminar, I will show how the discovery of a giant hydrogen exosphere around the warm Neptune GJ436b has changed our understanding of upper atmospheres, opening thrilling perspectives for the characterization of small, mildly irradiated exoplanets, and how this field is evolving from space-borne ultraviolet observations to ground-based, high-resolution spectroscopy at visible and infrared wavelengths.
To fully understand the nature and evolution of an exoplanet, its atmospheric properties must be studied along with its dynamical history: where did a planet form and what material did it accrete as a result ? when did a planet migrate close to its star and start to lose its atmosphere? These questions can be addressed by measuring the present orbital architecture of a planetary system, which traces its past dynamical evolution. Yet these architectures are mostly known for giant planets around solar or earlier-type stars, limiting our ability to relate these measurements to the actual history of a planetary system. In the second part of this seminar, I will show how the development of a new observational technique has led to the first measurement of a M dwarf system architecture, and its implication for our understanding of the evolution of close-in planets.
These new approaches to the characterization of atmospheric and orbital properties, combined with the arrival in the coming months of new-generation spectrographs in the visible (ESPRESSO) and near-infrared (SPIRou), will allow the Community to study in details the properties of the many small exoplanet systems that will be discovered by upcoming transit surveys (TESS, CHEOPS, PLATO), especially around M-dwarfs.
Image by Denis Bajram (LICENSE CC BY-NC-SA 4.0)