Simulations of planet formation tend to give us planets forming in a disk-like configuration, similar to what we observe in our own Solar System. (Thomas Quinn et al., Pittsburgh Supercomputing Center)

Why Do All The Planets Orbit In The Same Plane?

The possibilities were almost limitless, so why does everything line up?

Our Solar System is an orderly place, with the four inner planets, the asteroid belt, and the gas giant worlds all orbiting in the same plane around the Sun. Even as you go farther out, the Kuiper belt objects appear to line up with that same exact plane. Given that the Sun is spherical and that there are stars appearing with planets orbiting in every direction imaginable, it seems too much of a coincidence to be random chance that all these worlds line up. In fact, practically every Solar System we’ve observed outside of our own appears to have their worlds line up in the same plane, too, wherever we’ve been able to detect it. Here’s the science behind what’s going on, to the best of our knowledge.

The eight planets of the Solar System orbit the Sun in almost an identical plane, known as the Invariable Plane. This is typical of solar systems as we know them so far. (Joseph Boyle of Quora)

Today, we’ve mapped out the orbits of the planets to incredible precision, and what we find is that they go around the Sun — all of them — in the same two-dimensional plane, to within an accuracy of, at most, 7° difference.