Giant Planet Formation in the Solar System

The formation of gas giants has greatly influenced the structure of our solar system while their evolution has played a crucial role in shaping its history. Consequently, the growth of Jupiter has been studied quite extensively. However, little attention has been paid to Saturn and the other giants in the outer solar system.

Here we explore, through 𝑁-body simulations, the implications of the simplest disc and pebble accretion model on the formation of the giant planets in the solar system. A steady-state accretion scenario with an assumed ring structure in the disc at 5 AU was adopted for the simulations. A 10-parameter space was explored, including disk parameters related to gas — such as the gas diffusion rate and the strength of disk turbulence — as well as parameters concerning planetesimals, including their number, mass, and spatial distribution.

In this framework, giant planet formation is most sensitive to the accretion sticking efficiency in addition to all the gas disk parameters. The probability distribution of the final location of the giant planets is approximately constant in log r, suggesting there is a slight preference for formation closer to the Sun, but no preference for more massive planets to form closer. We compute the average formation time for proto-Jupiter to reach 10 Earth masses to be 1.1 ± 0.3 Myr and for proto-Saturn 3.3 ± 0.4 Myr, while for the ice giants this increases to ~5 Myr.

The formation timescales of the cores of the gas giants are distinct, suggesting that they formed sequentially. Accordingly, ice giants formed at the very end of the gas disc’s lifetime resulting in their low gas mass. A larger parameter space and extended simulation times are required to capture the full range of possible outcomes, with particular emphasis on producing all three types of giant planets within a single simulation.