How planetesimal accretion affects the composition of gas giants

Planet formation is still a debated process in the scientific community. The state of art theories predict planets to form inside protoplanetary disks made of gas and dust orbiting around newly formed stars. Dust particle in the disk tend to settle towards the midplane and to grow into bigger sized particles, called pebbles. They can also grow into m to km size objects, the planetesimals, as result of instabilities in the disk. Planets subsequently form as these particles aggregate, but the exact process that leads to planet formation is still an open question. In particular we still do not know for sure whether planets form accreting only planetesimals, only pebbles or if they are the result of a combined process. Indeed, as the number of detected planets increases with time (expecially since the launch of JWST), we discover new types of planets whose formation is hard to explain with current models. The main aim of this thesis is to investigate the impacts that planetesimal accretion has on the final composition of planets, possibly answering the question whether the planet’s composition is able to constraint its formation pathway. To do so, we investigated three different planet formation scenarios: pebble accretion, pebble accretion with planetesiaml formation (but not accretion) in the disk and finally a scenario of both pebble and planetesimal accretion. We simulated, for every scenario, the birth and growth of planetary seeds planted at different initial distances from the central star and tracked the planets’ composition as they grew. The simulations were performed using a 1D semi-analytical code able to track the planets’ chemical compositions as they grow and migrate through the disk. Then we proceeded to analyse the planets’ growth tracks, with focus on the C/O ratios in the atmosphere, final heavy element contents and volatile to refractory ratios. We found that indeed the accretion of planets via planetesimal produces planets with different compositions with respect to the pebble accretion scenario. In the future, we may apply this analysis on data coming from JWST observations.