In most representaions of the solar system, you will see that the orbits or all satelitites of the sun all lie on a 2 dimentional planel. Is this actually the case, and why?

This message has been edited. Last edited by: DorianGreyed,

From the figures below, which are the degrees by which the other planets are inclined to the orbit of earth, you can see that all but Pluto lie in a very shallow plane.

Name.....Inclination.
Earth.......0.000
Uranus......0.774
Jupiter.....1.308
Neptune.....1.774
Mars........1.850
Saturn......2.488
Venus.......3.394
Mercury.....7.004
Pluto.......17.148

This occurs because the material from which the planets were formed spun around the Sun in a very flat disk.

This isn't a requirement, however. Some of the planets we're discovering that orbit other stars have orbits that are not "co-planar" -- not orbiting in almost the same plane.

Planets also don't have to have orbits with their star roughly in the center of the circular orbit. If the planet's orbit is such that it sometimes comes very close to its star and sometimes moves very far away, the orbit is called "eccentric".

In our Solar System, the planet Pluto comes closest to fitting these two descriptions. As you can see from Minnesota's chart, Pluto's orbit is tilted a good bit in comparison to the other planets' orbits. And Pluto's orbit is eccentric enough that it is sometimes closer to the Sun that Neptune, making Pluto the "8th planet", and sometimes farther from the Sun than Neptune, making Pluto the "9th planet".