From Solar System to Exoplanets: What can we learn from Planetary Spectroscopy?

International audienceThe purpose of this paper is to address the question: Using our knowledge of infrared planetary spectroscopy, what can we learn about the atmospheres of exoplanets? In a first part, a simplified classification of exoplanets, assuming thermochemical equilibrium, is presented, based on their masses and their equilibrium temperatures, in order to propose some possible estimations about their atmospheric composition. In the second part, infrared spectra of planets are discussed, in order to see what lessons can be drawn for exoplanetary spectroscopy. In the last part, we consider the solar system as it would appear from a star located in the ecliptic plane. It first appears that the solar system (except in a few specific cases) would not be seen as a multiple system, because, contrary to many exoplanetary systems, the planets are too far from the Sun and the inclinations of their orbits with respect to the ecliptic plane are too high. Primary transit synthetic spectra of solar system planets are used to discuss the relative merits of transmission and direct emission spectroscopy for probing exoplanetary atmospheres