The near-circular orbits of the major planets in our Solar System are not solely the result of the net rotational momentum of the accretion disk at its formation, although it did play a role. The process of planetary formation is complex and involves various factors that contribute to the final characteristics of the orbits.
During the early stages of the Solar System's formation, a rotating disk of gas and dust known as the protoplanetary disk surrounded the young Sun. As this disk gradually collapsed under the force of gravity, it formed clumps of material called planetesimals. These planetesimals further collided and merged, eventually forming protoplanets, which then evolved into the planets we see today.
The angular momentum of the rotating protoplanetary disk did influence the initial motions of the forming planets. Conservation of angular momentum means that as the protoplanetary disk contracted, it caused the material closer to the center to rotate faster than the material farther away. This differential rotation can result in the net angular momentum of the disk being transferred to the forming planets.
However, the circularization of planetary orbits is not solely attributed to the rotational momentum of the disk. Other processes come into play as well, including tidal interactions, resonances, and gravitational interactions between the planets themselves.
Jupiter, being the largest planet in our Solar System, did have a significant impact on the formation and evolution of the other planets. Its strong gravitational influence disrupted the orbits of nearby planetesimals and prevented them from accreting into a single large planet. Instead, it contributed to the formation of a significant asteroid belt between Mars and Jupiter. Jupiter's gravity also affected the orbital dynamics of the other planets, causing slight perturbations that can lead to resonances and orbital interactions.
In summary, the near-circular orbits of the major planets in our Solar System are the result of a combination of factors, including the net rotational momentum of the accretion disk, interactions with other forming planets, and various dynamical processes that occurred during the planet formation phase. The specific role of Jupiter and the impact of random collisions are still topics of ongoing research and study in the field of planetary science.