Final answer:
The outer planets in the solar system formed primarily through gravitational forces combined with the accretion of planetesimals. Protoplanets grew larger by attracting ices and rocks, and eventually gas, resulting in the gas giants like Jupiter and Saturn. These processes of accretion and gravitational forces led to planetary differentiation and the current state of the outer planets.
Step-by-step explanation:
The outer planets of the solar system were formed primarily through the process of gravitational forces acting on the material in the solar nebula. As the solar nebula collapsed, material fell toward the center, becoming hotter and more concentrated. This resulted in the formation of protoplanets that grew larger from the accumulation of ices and rocks. These protoplanets became so massive that they could attract and retain surrounding gas, particularly hydrogen and helium, leading to the creation of the gas giants such as Jupiter and Saturn. Gravitational forces were the dominant factor in this process, enabling these large protoplanets to gather more material and heat up due to the energy of contraction.
Planetesimals collided and stuck together, forming larger bodies, which is known as accretion. As these bodies accreted more material, they differentiated due to the heat from the impacts and the gravitational compression, causing heavy elements to sink and lighter elements to rise. After a few million years of impacts and accretion, the planets formed, eventually cooling down to their current states.