WG1: Understanding the formation and evolution of planetary systems and habitable planets

Leaders:
 - E. Szuszkiewicz (Poland): Planetary Formation and Evolution
 - Lena Noack  (Belgium): Star Formation and Evolution 
 - Florian Gallet (Switzerland): Habitability

Planet formation is intrinsically connected to the physical and chemical properties of the host star and its circumstellar material. In particular gaining an understanding of processes such as the evolution of the host star’s luminosity versus its mass and its main sequence progress, the distribution of elements in the protostellar disk and its chemical structure, the dynamics of grains and volatiles in the presence of a gas cloud, and the chemical composition of the star are all central to understanding of planetary formation and evolution  and developing state-of-the-art stellar models. These models should also include very specific magneto-hydrodynamical processes (e.g., magnetic interaction between the star and its accretion disk, angular momentum redistribution, chemical mixing, tidal forces, etc.) that are not yet fully understood but are known to be crucial to explain key observational features of proto-stars and young stars.

The commonality of Sun-like stars in the Milky Way strongly suggests that many stars in our galaxy hosts planetary bodies, some of which might be habitable, indeed around nine hundreds exoplanetary bodies and more than three thousands planetary candidates have now been discovered with the prospect of many more being revealed as Kepler’s data is analysed . The presence of several low-mass planets orbiting their host stars in their Habitable Zones (HZ) suggests that many Earth-like habitable planets exist. Upcoming space missions and ground-based telescopes (e.g., ELT Extreme Large Telescope) are expected to identify many more of these bodies and will provide the opportunity for  characterizing  their atmospheres and hence exploring their potential  for supporting life.

It is therefore timely to study the origin as well as the physical and dynamical characteristics of these objects. Such studies require a detailed theoretical approach to develop comprehensive models for the formation and evolution of planetary bodies, and particularly the habitable ones. It is then necessary to develop a deeper understanding of:

1. The formation of giant planets, super-earths, and smaller bodies,
2. The processes of their dynamical evolution such as planetary migration, planet-planet scattering, and their long-term stability, and within the context of habitability,
3. Their atmospheric characteristics and their interior properties.

Within this context, the Action will address the challenge of gaining a fuller understanding of planetary systems and habitable planets by :

1. Developing custom-made stellar models that include specific magneto-hydrodynamical processes
2. Investigating accretion processes in the range of  submillimeter to centimeter (fluffy aggregates and grains), meter to kilometer (planetesimals) and several kilometers (planetary embryos)
3. Simulating  the evolution of protoplanets in the protoplanetary disc, including dynamical processes affecting their inward and outward migration
4. Studying the evolution of planetary systems and investigating in particular the processes determining the final state (rotational speed, orbit eccentricity). To what extent are these processes stochastic (chance collisions) or predictable (interaction with neighbouring giant planets)?
5. Model the final architecture of planetary systems, particularly those with low mass planets orbiting in the habitable zones of their host stars
6. Developing new and sophisticated numerical techniques to study and model exoplanetary atmospheres to identify biosignatures
7. Developing sophisticated models of the interior of Earth-sized and super-Earth extrasolar planets, and determine the connection between their interior dynamics and atmospheric structure
8. Investigating whether or not our solar system is typical or similar to other exoplanetary systems

These tasks require combined expertise from astrophysics, geosciences, atmospheric science, chemistry and also history of science which will deal with the history of planetary sciences and the emergence of  a new interdisciplinary field called “astrobiology”.