Terrestrial planet formation during giant planet formation and giant planet migration I: The first 5 million years

Abstract

Terrestrial planet formation (TPF) is a difficult problem that has vexed researchers for decades. Numerical models are only partially successful at reproducing the orbital architecture of the inner planets, but have generally not considered the effect of the growth of the giant planets. I dynamically model TPF as the gas giants Jupiter and Saturn are growing using GENGA. The evolution of the masses, radii and orbital elements of the gas giants are precomputed and read and interpolated within GENGA. The terrestrial planets are formed by planetesimal accretion from tens of thousands of self-gravitating planetesimals spread between 0.5 au and 8.5 au. The total mass of the inner planetesimal disc and outer disc are typically 2 and 3 Earth masses respectively, and the composition of the planetesimals changes from non-carbonaceous-like to carbonaceous-like at a prescribed distance, ranging from 2 au to 5 au. After 5 Myr of evolution approximately 10% to 25% of the mass of planetesimals in the Jupiter-Saturn region is implanted in the inner solar system, which is more than what cosmochemical models predict. The implantation initially sets up a composition gradient in the inner solar system, with the fraction of outer solar system material increasing with increasing distance to the Sun. The planetesimals that remain in the inner solar system have a mixed composition. The growth of the gas giants scatters planetesimals in their vicinity into the inner solar system, which changes the isotopic composition of the terrestrial planets. The planetesimal disc in the vicinity of the gas giants may not have been very massive, ~1 ME. The inner planetesimal disc may not have extended much farther than 2 au otherwise embryos do not grow fast enough to produce Mars analogues. This could mean that the region of the current asteroid belt never contained much mass to begin with.