In the 1st work package, we have included a new method to calculate the structure of protoplanetary discs with a self consistent calculation of the grain size distribution in the disc dependent on the temperature which in itself depends on the grain sizes, which has never been done before. The results of these simulations allow for the first self-consistent simulations of the structure of the disc in the inner regions, where observations can not penetrate into the disc due to the obscurence by the stellar irradiation. The results have been published in Savvidou et al. 2020. We further studied the importance of this process for the formation of inner super-Earths, where we showed that the observed mass distribution can only be achieved by early planet formation (Savvidou & Bitsch 2021). In addition, we showed that the effect of grain growth at the water ice line could cause pressure perturbations in the disc, beneficial for planet formation (Müller et al. 2021). This work is fundamental to understand the interplay between inward drifting pebbles, disc structures and planet formation.
For the 2nd work package we have included for the first time the accretion process of giant planets into their gap opening behavior, which was previously thought to happen mainly due to an exchange of angular momentum between the planet and the surrounding gas. The results of these simulations indicate that gas accretion is an important process for giant planets to open gaps in protoplanetary discs that should not be ignored in future simulations (Bergez-Casalou et al. 2020). We extended this study to include how 2 planets can accrete simultaneous and influence their growth (Bergez-Casalou et al. 2023), show that Saturn indeed needs to form later than Jupiter to achieve the current mass ratio. We further showed that low resolution observations of protoplanetary discs can have problems to distinguish how many planets could be hidden in discs (Bergez-Casalou et al. 2022) and that not all gaps can contain planets (Tzouvanou et al. 2023).
For the 3rd work package, we have already presented the first simulations that combine pebble accretion, planet migration and N-body interactions after the protoplanetary disc dispersed after a few Myr to study the formation of planetary systems containing super-Earths and gas giants (Bitsch et al. 2019, 2020). We find that in particular the dynamical instabilities within planetary systems after the gas disc phase have important consequences how many planets can be detected by observations. We also show that the structure of these systems depends on the presence of outer gas giants that can cause instabilities of the inner planetary systems (Bitsch & Izidoro 2023). We show that the inner super-Earth systems have different structures (e.g. eccentricities) depending on the presence of outer gas giants, indicating that follow up radial-velocity observations of these systems can give further constraints to planet formation simulations.
Finally our project deals with studying the chemical composition of discs and planets. In particular, we find that inward drifting pebbles that cross evaporation fronts can enrich the discs to super-solar values, in contrast to the previously assume static picture of disc chemistry (Schneider & Bitsch 2021a,b, Mah et al. 2023). We show that inward drifting and evaporating pebbles are a crucial ingredient to explain the composition and heavy element content of giant planets (Bitsch et al. 2022, Bitsch & Mah 2023), as these models can explain sub- and super-solar compositions at the same time.
