Science Questions

Why do all planets orbit in almost the same plane?

Tue, 25th Sep 2012

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Muhammad Al-Hakeem asked:

Why do all planets revolve around the Sun in almost the same plane?


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I truly do not know for sure.

However while fooling with some Hematite magnets. I noticed that if you spin one of the magnets, the other a few inches away starts to spin. As if some how connected to the other. Very interesting I thought.

If the sun is rotating and some believe it is. That might explain it. Why mercury rotates in the opposite direction might take some more explaining, but, I was impressed by the Hematite magnets.


                            William McCormick William McCormick, Sun, 12th Aug 2012

One popular theory is that the planets formed out of a flat spinning disk of gas and dust (a similar shape to our galaxy).

The disk was spinning in one direction, and any small amounts of matter traveling in other directions would have collided with the main mass, and been absorbed. evan_au, Sun, 12th Aug 2012

Lmnre, Sun, 12th Aug 2012

Galaxies, Solar Systems, Moons, and Planetary Rings all tend to have generally planar orbits (except perhaps the central bulge in larger galaxies).

But, of course the orbits aren't perfectly planar.

I would think this would have to with the gravitational interactions between planets to some extent.  I.E.  Whenever on Jupiter's side of the sun, Earth gets pulled somewhat closer to Jupiter and Jupiter's plane.  When opposite Jupiter, Earth gets pushed further away from Jupiter, and correspondingly toward Jupiter's plane.

The inner planets would experience stronger solar tides, and would move closer to the sun's equatorial plane. CliffordK, Mon, 13th Aug 2012

if you imagine a large cloud of gas and dust -- does not have to be flat or spinning -- and consider what is going to happen to it as it gravitationally collapses.

Initially in our model there will be numerous pieces moving independently with random positions and velocities. The angular momentum of the cloud will not be zero -- it will have a most probable angular momentum, governed by statistical factors. Whatever angular momentum it does have must be conserved.

As the gravitational collapse continues kinetic energy of motion of the fragments is gradually converted into heat energy, and the cloud becomes a smaller cloud. Because of conservation of angular momentum it will also be spinning -- and start to show a coherent rotation which will become faster and faster as the cloud gets smaller and smaller. It is like an extreme form of a skater pulling her arms in. But when a central star starts to form, its rate of spinning just cannot keep up, and some of the cloud must move away from it in a flat disk to maintain that angular momentum. Gradually the flat disk will istelf collapse into planets. But the initial angular motion -- a small total angular velocity in a large cloud -- nust conserve its angular momentum. So everything -- the rotation of the star, the orbits of the planets, and the rotations of the planets, will be moving in pretty much the same angular direction in pretty much the same plane when the angular momentum of that motion must be imposed on a much smaller solar system. damocles, Tue, 14th Aug 2012

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