Periodic Reporting for period 4 - PAMDORA (Planetary accretion and migration in discs over all ages)
Okres sprawozdawczy: 2022-07-01 do 2023-11-30
After the discovery of the first planets outside of our own solar systems, we have wondered how these strange new worlds could have been formed. In particular, these so called exoplanets, are not at all like the planets in our own solar system. In fact the first exoplanet detected was a hot Jupiter, a Jupiter-type planet that orbits its host star in just a few days. Even though a hot Jupiter was the first exoplanet to be detected around a solar type star - a discovery that was awarded with the Nobel prize in 2019 -, these planets are actually quite rare and only 1-2% of all stars should host one. Recent observations and analysis have revealed that super-Earths, planets a few times the mass of the Earths, are the most abundant type of planet within 1 AU to their host star and that nearly 50% of all stars should host super-Earths. This makes us wonder if the solar system, where neither hot Jupiters or super-Earths exist, is strange in itself. This ERC starting grant deals with simulations to understand how planets and planetary systems can form.
Planet formation in itself is a complex process that starts with grain growth in protoplanetary discs, which surround the newly born stars, to form pebbles of mm-cm in size that can then form 100km sized objects - so called planetesimals - when a cloud of pebbles collapses under its own gravity. These planetesimals can then grow by accreting other planetesimals or pebbles to form planetary cores of a few Earth masses, which can then start to accrete gas from the protoplanetery disc to become gas giants. At the same time, the growing planet interacts gravitationally with the gas disc and migrates through it. In order to simulate this complex process simulations over several magnitudes in size (from mm sized grains to Planets with thousands of km radius) and mass (from small grains with weights less than a gram to planets with masses of 10^30 gram or more) are needed. However current computers are not strong enough to simulate all these processes in detail in one simulation. Therefore different simulations are needed to understand single processes in detail.
The objectives of this ERC grant are to study in detail the structure of the protoplanetary discs, how planets migrate in these discs and how planetary systems can emerge from their discs. For this, we use hydronamical and N-body methods. The goal of these simulations is to understand how planetary systems form and how the solar system came to be, answering part of the oldest questions of humanity: why are we here?
Planet formation in itself is a complex process that starts with grain growth in protoplanetary discs, which surround the newly born stars, to form pebbles of mm-cm in size that can then form 100km sized objects - so called planetesimals - when a cloud of pebbles collapses under its own gravity. These planetesimals can then grow by accreting other planetesimals or pebbles to form planetary cores of a few Earth masses, which can then start to accrete gas from the protoplanetery disc to become gas giants. At the same time, the growing planet interacts gravitationally with the gas disc and migrates through it. In order to simulate this complex process simulations over several magnitudes in size (from mm sized grains to Planets with thousands of km radius) and mass (from small grains with weights less than a gram to planets with masses of 10^30 gram or more) are needed. However current computers are not strong enough to simulate all these processes in detail in one simulation. Therefore different simulations are needed to understand single processes in detail.
The objectives of this ERC grant are to study in detail the structure of the protoplanetary discs, how planets migrate in these discs and how planetary systems can emerge from their discs. For this, we use hydronamical and N-body methods. The goal of these simulations is to understand how planetary systems form and how the solar system came to be, answering part of the oldest questions of humanity: why are we here?
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.
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.
Within this project, we have already advanced significantly our understand of protoplanetary discs and planet formation. The new simulations of the protoplanetary disc are the first of their kind that include full grain size distributions in order to calculate the thermal structure of the disc, where the grains are responsible for the cooling of the disc. These simulations will allow in the future for more accurete simulations of planetary growth and to understand better the structure of protoplanetary discs (Savvidou et al. 2020).
In addition, we have presented the first simulations that included pebble accretion, planet migration and dynamical instabilities in an N-body environment. The results of these simulations were published early last year in a series of 3 papers that have already received over 100 citations each. The publications for this main result are Lambechts et al. (2019), Izidoro et al. (2019) and Bitsch et al. (2019a).
We have also shown how inward drifting and evaporating pebbles influence the disc structure and planetary composition (Schneider & Bitsch 2021a, b, Bitsch et al. 2022) changing the picture from the previously assume static compositions of discs. This model is becoming more and more of standard in our understanding of discs and planets.
In addition, we have presented the first simulations that included pebble accretion, planet migration and dynamical instabilities in an N-body environment. The results of these simulations were published early last year in a series of 3 papers that have already received over 100 citations each. The publications for this main result are Lambechts et al. (2019), Izidoro et al. (2019) and Bitsch et al. (2019a).
We have also shown how inward drifting and evaporating pebbles influence the disc structure and planetary composition (Schneider & Bitsch 2021a, b, Bitsch et al. 2022) changing the picture from the previously assume static compositions of discs. This model is becoming more and more of standard in our understanding of discs and planets.