In the last few years, we opened a new window on planet formation by discovering a sample of planets still embedded in their natal disk. The opportunity to directly study these early stages of planet assembly requires a better knowledge of the physical and chemical evolution of the disks feeding forming planets and the rapidly changing environment shaping the planet-disk interaction.

This session will cover planet formation models at different stages of disk evolution, from its birth to its final dispersal as well as observations of disks and exoplanet atmospheres that can help to constrain these models. The goal is to bring together different communities studying planet and disk evolution and to drive a discussion on this fundamental but mostly overlooked phase. This will enable us to elucidate the formation pathways of planets during the disk stage and establish connections between the variety of planets discovered and the diversity of protoplanetary disks and their respective environments. In addition, a specific emphasis will be placed on multi-planetary systems, in which differences in physical properties and chemical composition arise not from underlying variability but directly from the evolution of the disk.

1. Early formation of planet-building blocks

The early stages of disk evolution are the more dynamic, with massive disks forming and settling. In this scenario, several theoretical works have envisioned an enhanced probability of fast formation of the primordial cores of giant planets. However, these systems are still very embedded and clear observational evidence of disk substructure is still lacking (see the recent eDisk survey, Ohashi et al. 2023). This block will discuss the potential of planet formation during the Class 0/I phase and its impact on the disk's chemical evolution, dust disk lifetime, and multi-planetary systems.

2. Planetary core assembly in a chemically evolving disk

The chemical inventory available to a forming planet depends on the location and time of formation. The chemical variability within a system is mainly driven by the radial drift and evaporation of pebbles, which in turn is affected by the growth of dust particles from micrometer size up to km-sized planetesimals. Dynamical interaction between the disk and the forming planet will also directly affect the dust distribution, as well as the final location and composition of the planet once the disk has dispersed. JWST and the future ARIEL mission will bring a wealth of data regarding C/O, O/H and other chemical species in planetary atmospheres, informing theoretical models. This block will focus on the influence of disk evolution and planet-disk interaction on the chemical composition of forming planetary cores and atmospheres. In particular, the chemical differences within multi-planetary systems are driven by the timing of subsequent planet formation within the evolving disk.

3. Planet-forming disk observations

In the past ten years ALMA has revolutionised our understanding of planet formation by imaging a large sample of disks at high angular resolution in nearby star forming regions, both in the dust continuum and spectral lines. It showed us that substructure is present in disks of every age, where planet formation is potentially at play, shaping the disk and affecting the dust dynamics. In particular, ALMA spectral line observations gave us a powerful tool to study the chemistry and abundance variations within disks that affects the atmospheric composition of forming planets. Finally, with PDS 70, we were able to directly detect young planets still embedded in their natal disk. This block will focus on the recent results of circumstellar disk observations in the context of planet formation at different stages of disk evolution and in distinct environments.

4. Environmental effects on planet formation

Protoplanetary disks are not born in isolation. Stellar multiplicity affects the disk evolution for its entire lifetime. Other effects like infall, external photoevaporation and close encounters are more important in the early stages while the star is still embedded in its birth cluster. These effects take place while the first planetary cores are developing in a fully-fledged planetary system. They can thus strongly affect its final configuration by cutting the supply of material, refreshing it with enriched one, and exciting their inclination and eccentricity. Isotopic anomalies observed in meteoritic material can also be explained by the late infall of material after the initial formation of the protosolar nebula, which suggests the importance that these processes might have also had in the formation of our own Solar System. In this block, we will assess the importance of these different environmental effects and identify the ones that need a better understanding in the future.

5. Planet formation during disk dispersal

Disk evolution happens in a two-timescale scenario, with a slow viscous/MHD wind-driven disk evolution followed by a fast disk removal that freezes the ongoing giant planet formation and migration processes. The timing of dispersal, given by the magneto-thermal disk winds and environmental effects, will shape the planetary system architecture. In this block, we will study the predictions of the time available for planet formation around different stellar types and the role of disk dispersal in shaping the planetary architecture (i.e. by halting the planet migration and breaking resonances).

6. Connecting planetary atmospheres with their birth environment

The advent of the James Webb Space Telescope and the future dedicated european ARIEL mission, together with ground-based high-resolution spectroscopy, will allow us to have the spectral coverage and precision to move from simple detection to quantification of molecular abundances. This is a necessary step to connect exoplanetary atmosphere composition to their formation processes and environment. In this block, we will focus on the link between atmospheric characterization and planet formation models.

Programme

1.	Early formation of planet-building blocks		2.	Planetary core assembly in a chemically evolving disk
3.	Planet-forming disk observations		4.	Environmental effects on planet formation
5.	Planet formation during disk dispersal		6.	Connecting planetary atmospheres with their birth environment

Invited speakers

1.	Łukasz Tychoniec, Leiden Observatory, Netherlands		2.	Michiel Lambrechts, University of Copenhagen, Denmark
3.	Giulia Perotti, Max Planck Institute for Astronomy, Heidelberg, Germany		4.	Sierk van Terwisga, Space Research Institute, Graz, Austria
5.	Andrew Sellek, Leiden Observatory, Netherlands		6.	Giovanna Tinetti, University College London, UK

Scientific organisers

☆	Giovanni Picogna LMU Munich, Germany, chair		☆	Joanna Drążkowska Max Planck Institute for Solar System Research, Göttingen, Germany, co-chair
☆	Bertram Bitsch University College Cork, Ireland		☆	Nienke van der Marel Leiden Observatory, Netherlands
☆	Michael Küffmeier University of Copenhagen, Denmark		☆	Anna Penzlin Imperial College London, UK
☆	Alexandros Ziampras Queen Mary University of London, UK

Contact

Giovanni Picogna giovanni.picogna @ pm.me
Joanna Drążkowska drazkowska @ mps.mpg.de