Wallenberg Academy Fellow grant (extension)
Astronomers know today of more than three thousand exoplanets – planets that orbit stars other than the Sun. Observations show that nature forms a large variety of planets. Some stars host giant planets like Jupiter, but in orbits much closer the star. Other planetary systems contain several super-Earths, more massive counterparts to the terrestrial planets in our Solar System. The aim of this project is to connect the emergence of these different planetary classes to the formation of kilometer-sized planetesimals around young stars. The asteroids in the Solar System represent the remnant of the planetesimals that formed around our young Sun more than 4.5 billion years ago. I have previously developed models for the formation of planetesimals, by the gravitational collapse of regions overdense in pebbles, and used these to explain why the dominant size of asteroids is approximately 100 km and why comets appear to be made entirely out of pebbles. For this project I will address the formation location and timing of planetesimals. I will develop a model framework where planetesimals form in three generations. The first generation forms at the ice lines of molecules such as water and carbonmonoxide and drives the early growth of gas giants and super-Earths with gas atmospheres. The second generation forms in extensive discs of pebbles, similar to the ring system of Saturn, that orbit growing planets. I will model how such discs fragment to form planetesimals that accumulate to moon systems around giant planets and super-Earths. The third generation forms as the gas escapes from the protoplanetary disc through winds. These planetesimals drive the formation of terrestrial planets like our Earth. I will use this three-generation model to simulate the formation of planetary systems that can be directly compared to the ever-expanding catalogue of exoplanetary systems.