Planetary allignment

[BobbyJoeCool]

Why is is that most of the planets of the solar system all lie pretty close to a plane? Is there something special about it?

 

Sorry for sounding stupid...

[swansont]

Why is is that most of the planets of the solar system all lie pretty close to a plane? Is there something special about it?

 

Sorry for sounding stupid...

 

Conservation of angular momentup and collisions. Conservation of angular momentum gives you rotation, and out-of-plane orbits tend to eventually lead to a collision.

[BobbyJoeCool]

do you mean angular momentum created by the rotation of the sun? (eg: the planets align in a plane because the sun is rotating).

 

And... out of plane=collision... collision with what? other objects in orbit? objects that won't come into orbit (passerby comets and whatnot)

[ecoli]

I was under the impression that our solar system was rather unique in having co-planar orbits. Was I wrong?

 

 

edit: http://zebu.uoregon.edu/~imamura/121/lecture-2/planet.html

* The motions of the planets are roughly confined to the ecliptic. This implies that the orbits of the planets are roughly co-planar with the orbit of the Earth about the Sun.

 

* Not as obvious is the fact that all planets orbit the Sun in the same sense as does the Earth. This means that they usually move in the west-to-east direction on the Celestial Sphere (CCW as viewed from the NCP). However, an exception to this motion is the retrograde motion sometimes exhibited by the planets (see below).

 

* The planets' orbits are all roughly circular in shape.

 

The preceding facts are interesting (and profound) because they suggest that the planets in our Solar System formed as a single unit rather than as individual planets which were later assembled into the Solar System.

[swansont]

do you mean angular momentum created by the rotation of the sun? (eg: the planets align in a plane because the sun is rotating).

 

And... out of plane=collision... collision with what? other objects in orbit? objects that won't come into orbit (passerby comets and whatnot)

 

Angular momentum present in the whole cloud of material that formed the solar system - the sun formed out of the material, as did the planets, with the sun having most of the mass. But the planets carry a large chunk of the angular momentum - I think the sun simply can't spin fast enough. The rotation of the sun, and the planets, are both the result of angular momentum present in the nebular cloud that formed the solar system. Or so the model goes, AFAIK.

 

Out-of-plane collisions with anything - other out-of-plane objects or even in-plane objects. You are left with objects that can't collide or interact gravitationally to the point where an unstable orbit is formed, or at least such interactions are separated by very long periods of time.