Exoplanets

Research topics

Over the past 30 years, the study of exoplanets has evolved from a niche subject based solely on theoretical considerations to a major research field within astronomy. Our empirical understanding of planet diversity and formation has expanded from the few planets in our Solar System to over 5,700 exoplanets, confirming that planets similar to those orbiting our Sun are commonplace, and that the diversity of exoplanets is far greater than we could have suspected from our initial sample of 8 planets. These are exciting times for the study of these new worlds, and we’re laying the foundations for the search for extraterrestrial life. It was against this backdrop that IPAG’s Exoplanets team was created 10 years ago. Its birth, out of the former FOST team (covering a wider field as it corresponds to the current Odyssey and Exoplanets teams), was motivated by the growth of the exoplanet research theme within the French astronomical community, and particularly at IPAG.

Our main scientific topics and research objectives are:

• Detecting exoplanets
  • Towards an understanding of exoplanetary systems as a whole and in all their diversity
  • Detecting planets that can be characterized.

• Characterizing exoplanets
  • Atmospheric diversity, from telluric planets to gas giants.
  • Fundamental parameters of planets: mass, radius, luminosity, etc.

• Origin of life
  • How common are habitable planets?
  • What are the limits of habitability? How can we search for signs of life on exoplanets?

Further information :

The team is heavily involved in major surveys (SPIROU, HARPS, NIRPS) aimed at detecting exoplanets, particularly around M dwarfs. This effort targeting low-mass host stars is complemented by the effort initiated at IPAG to search for and characterize exoplanets by transit with the EXTRA observatory. These detection efforts are underpinned by several of the team’s studies focused on understanding the processes of stellar variability and activity, which, in addition to their impact on stellar physics, also help to limit and identify the impact of stellar activity on exoplanet detection (false positives/negatives and bias in parameter determination). These approaches mainly target exoplanets relatively close (typically <1 AU) to their star. At larger separations, and in the particular case of young systems, the team is heavily involved in the detection of giant planets, during or just after their formation period, via high-contrast direct imaging. This work, based in particular on the SPHERE instrument, is sometimes guided by dynamical clues to the presence of planets, thanks to the constraints provided by GAIA.The detection of exoplanets in these large surveys at IPAG, by both direct imaging and radial velocity, provides robust statistical constraints on exoplanetary populations, including planets in the habitable zone, and thus constrains the various models of planetary formation being carried out in other laboratories around the world.

Given the paucity of photons we receive from exoplanets, characterizing their physical parameters presents very special challenges, and relies in particular on obtaining the spectrum of exoplanets and detecting molecules in their atmospheres. This information comes quite naturally with direct imaging, for which we have access to the photons emitted by the planet itself, enabling us to constrain atmospheric physics in the case of giant planets. Transit and radial velocity, when these two methods are combined, give access to the density of the exoplanet under study, and the detection effort targets as a priority the planets most favorable for atmospheric characterization. This is reflected in the search for exoplanets around M dwarfs, whose closer habitable zone and favorable contrast help characterize planets, including some in the temperate zone. In parallel with this targeted characterization of exoplanets, part of the team is studying the overall architecture of the systems, the potential presence of multiple planets and dust, and the exocomets visible in the debris disks, with an emphasis on understanding the gravitational dynamics of these systems, sometimes making it possible to predict the existence of additional planets (such as Beta Pictoris c), or even to detect them directly and specify their masses, via TTV (Transit Timing Variations).

Beyond the purely astrophysical approach aimed at determining the frequency of exoplanetary systems with at least one telluric exoplanet in their star’s habitable zone, the team’s efforts to work on questions related to the emergence of life in the universe are structured primarily via the IDEX UGA Origin of Life CDP (“Cross Disciplinary Project”) funded since 2018 and renewed in 2021. The Exoplanet team plays a central role, with the PI and one of the three Co-Is as members. This project brings together nine laboratories, mainly in STU and chemistry-biology, as well as in SHS, around interdisciplinary questions on the emergence of life, conditions of habitability and tracers of extraterrestrial life. In addition to funding, Origin of Life has federated the Grenoble community around these major scientific challenges, integrating Exoplanets into a wider local network. In particular, it has enabled us to contribute to projects on the possibility of photosynthesis on planets orbiting red dwarfs, the limits of extremophilic biological processes in extraterrestrial environments, and AI applied to the detection and characterization of exoplanets.

Keywords

Planets and satellites: atmospheres, composition, detection, dynamical evolution and stability, formation, fundamental parameters; Planet-star interactions
; Zodiacal dust ; Stars: activity, fundamental parameters, Techniques: high angular resolution, image processing, imaging spectroscopy, interferometric, radial velocities
.