Thread: Why do all planets in the solar system appear coplanar?

The planets of our solar system orbit around the sun in 'almost' the same plane as the earth.

For one planet I can see why: given that the suns gravity acts as a central force, there is little in the way of other forces to lift the planet out of its plane of orbit.

But why do all planets lie in the same plane of orbit? If an incoming asteroid passed by the sun in a direction perpendicular to the usual plane of orbit as seen by the planets, would it align itself into that plane if it were to orbit the sun? Has it something to do also with how a lot of galaxies, with a centre of gravity, seem almost (but less so) 2-dimensional/flat?

It's currently believed that solar systems form from a disc-shaped dust cloud. Once the cloud is disc-shaped, anything formed from it will stay in the same disc until something knocks it out of line.

in addition to magimaster's well supported response, anything else is less stable.

if an asteroid were orbiting the sun in a manner perpendicular to the plane of the planets' orbits then it would be affected by the gravity of the sun and the gravity of the individual planets(on a much smaller level than that of the sun) over time as the planets went on their courses around the sun the gravitational pulls change and the vector of the gravitational pull on the object will change. this changes the direction the asteroid is traveling.

the same process would go on with the asteroid following a different orbit every second. the same applies to planets in the solar system but because they are on the same plane the vector doesn't change all that much.