Planetary orbits -- Why do planets orbit at same “level”?

[Josh0768]

TL;DR Summary

Why do planets orbit at same “level”?

Why is it that all of the planets in our solar system (to our knowledge) orbit the sun in such a way that they all go around the sun in roughly similar orbital planes? Why don’t we have planets with orbital planes at significantly different angles?

 

[BillTre]

Heritage of their origin from a rotating cloud of material in the form of a disk.

 

[Drakkith]

As BillTre said, the solar system formed from a collapsing cloud of material that collapses into a disk. The center of this disk collapses further to become the Sun, and other areas collapse into proto-planetary bodies. By nature of their initial position as part of this disk, the resulting planets are constrained to closely orbit in a plane unless they are perturbed significantly by planetary-sized objects, which is extremely rare.

 

[snorkack]

Also Kozai resonance.
Bodies that orbit at large angle to other bodies are liable to large perturbations that change their orbits to something else.
There are such bodies, like comet Hale-Bopp. But those are long period comets, that rarely enter into inner solar system to get perturbed again. Periodic comets don´ t last on high inclination orbits, and neither would planets.

 

[PeroK]

Summary:: Why do planets orbit at same “level”?

Why is it that all of the planets in our solar system (to our knowledge) orbit the sun in such a way that they all go around the sun in roughly similar orbital planes? Why don’t we have planets with orbital planes at significantly different angles?

Try this to start:



The flattening happened quite early in the solar system's development.

 

[snorkack]

Note that Kozai resonance only operates for large inclinations.
It does NOT operate for low inclination but retrograde objects. Which is why Halley comet is periodic - being at a low inclination orbit, it does not suffer from Kozai resonance. It is only comet sized, though - not a planet.
Of hot jupiters, a third (sic!) orbit retrograde to the rotation of star. How are the conditions about multiplanet systems? Has any multiplanet system yet been confirmed to contain planets orbiting in opposite directions? Solar System planets have been confirmed to orbit in the same direction, but any others?