The GJ 436 system : breakthroughs into the orbital and atmospheric characterization of exoplanets

To fully understand the nature and evolution of exoplanets, it is necessary to study their atmospheric properties along with their dynamical history, which can be inferred from their present orbital architecture (in particular the angle between the spin of a star and the orbital planes of its planets, or obliquity). Unfortunately, our lack of knowledge about the architectures of low-mass planets and cool-star systems has limited our ability to link orbital trajectory, planetary and stellar properties, and past evolution. I will show how the development of a new observational technique allowed us to determine, for the first time, the architecture of an exoplanet orbiting a M dwarf. Our detection of a highly misaligned orbit for the warm Neptune GJ436b joins other puzzling features of this planet: its eccentric orbit, its existence at the fringes of the evaporation desert, and the giant tail of neutral hydrogen that our team detected recently. I will show that these features might share a common origin, a dynamical scenario that could have led to the properties of other exoplanet systems similar to GJ436b.

GJ436b opened new windows into the orbital and atmospheric characterization of low-mass planets around cool stars, which will allow us to better look out at the many such systems that will soon be discovered by transit (eg NGTS, TESS, CHEOPS) and velocimetry (eg SPIRou, NIRPS) surveys.

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