Why are all planets in our solar system basically on the same plane?
As the cloud of gas and dust that formed our solar system collapsed to form the sun, it began to spin. The spinning motion formed a disk, in which the remaining material formed into the planets and asteroids. This is why they all orbit in the same direction and along the same plane. Comets are from the Oort cloud, which extends in every direction around the solar system, so their orbits are random, and not on the same plane as the planets.
