Grand tack hypothesis

The grand tack hypothesis proposes that the planet Jupiter formed at 3.5 AU. Then it migrated inward to 1.5 AU, before reversing course. This reversal happened because it captured Saturn in an orbital resonance.
Jupiter eventually stopped near its current orbit at 5.2 AU. Jupiter's planetary migration is known as the grand tack hypothesis.
Jupiter twice crossed the asteroid belt, scattering asteroids outward then inward. The present asteroid belt has a small mass, and a wide range of inclinations and eccentricities. This limited the material available to make Mars. It had long been thought that Mars was too small in comparison to its position in the Solar System. This was based on computer simulations of the early history of the Solar System.
Also, our new discoveries of planets in other star systems shows the Solar System as unusual. It is almost standard in other systems for the largest planet to be much closer to its star.