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Why Sun and the planets are in the same plane?

Posted: Thu Jun 27, 2013 1:52 pm
by Rajesh
Hi,

I have a question.

Why the planets in the solar system are in same plane with the Sun?

I searched in the net but got some vague answers like "It is due to gravity" :?

Re: Why Sun and the planets are in the same plane?

Posted: Thu Jun 27, 2013 3:15 pm
by johnson1010
Why the planets in the solar system are in same plane with the Sun?

Gravity.

Haha.

Here’s wikipedia’s article on it, and below is my somewhat more sloppy explanation.
http://en.wikipedia.org/wiki/Formation_ ... lar_System


Ok, so what happens is you start off with a big cloud of elemental dust called a nebula. The nebula that the sun came from was the remains of some probably second generation star going supernova.

The particles in the cloud attract eachother gravitationally. I’ve heard some rumbling that another supernova nearby may have kickstarted the process that got our nebula coalescing, but at any rate, particles begin to travel toward eachother, but they don’t all just fall strait in. They will have their own inertia from whatever circumstances they came from, and so one particle goes to move toward another, but ends up trailing it a bit.

The net motion of all these particles coming together, and chasing the motion of the particles they are gravitating toward begins a vortex motion. The conservation of angular momentum (retaining spin, essentially) means that the overall motion of the nebula will be in the direction of the most particle’s initial inertia.

Where particles are building up as they collect together causes an even stronger pull on those particles which are not yet a part of the grouped particles, producing a stronger gravitational pull toward those particles, and clearing out the regions “above” and “below” the angular plane of rotation of the cloud.

So, gravity pulls all the particles together, the particles continue moving with their initial inertia, plus the pull of gravity, causing them to circle in toward the center, which pulls the less influential clumps of matter into line behind them.

Clumps grow larger and large, becoming more gravitationally dominant and bigger and rounder all the time. They form asteroids, and planets and many of these have the wrong momentum to maintain a stable orbit around the cloud. These either fall into the center, or shoot off into space, or are arranged in wonky elliptical orbits which will ultimately bring them into conflict with another orbiting body, causing a collision.

So much matter (most of it hydrogen) collects in the center that thermo-nuclear-fusion begins, and the star lights up.

Most planets are also spinning in the same direction as the spin of the solar system, and this too owes to conservation of angular momentum. It’s the same process, but on a smaller scale.

So essentially the particles fall in a plane due to the momentum of gravitationally dominant particles, or masses, pulling the others behind, the sun is more or less at the center, and everything else falls into a plane because it is all balancing against itself. The things which would not stay in a stable orbit have been ejected from the system, or absorbed into dominant massive objects.

Re: Why Sun and the planets are in the same plane?

Posted: Thu Jun 27, 2013 3:57 pm
by ant
What is the cause of gravity?

(No - I am not looking for God in dark corners)

I know all about bigger bodies and smaller bodies.

Why is it "wimpy" at smaller distances?

Re: Why Sun and the planets are in the same plane?

Posted: Thu Jun 27, 2013 4:10 pm
by johnson1010
Haha, if i knew that, i would be a very famous man!

Solve that and you have got your name in the hall of physics fame, as well as a cushy job at a university.

Einstein said it was the way energy warps spacetime so that a particle traveling in a straight line across the "surface" of space-time appears curved. Like a marker drawing a line along a hoola-hoop, you might never change the straight path of the line, but the underlying structure of the hoolahoop takes your line into very curved paths.

Re: Why Sun and the planets are in the same plane?

Posted: Thu Jun 27, 2013 4:18 pm
by johnson1010
Gravity isn't just wimpy at smaller distance, by the way. it is 10 to the 43 times weaker than electromagnetic attraction.

What that means is the electric repulsion of two electrons is 10,000,000,000,000,000,000,000,000,000,000,000,000,000,000 times stronger than the gravitational attraction between them.

The reason for this vast difference is not known. The other forces are much closer in strength. Some theorists think that it may be that the other three forces are trapped in the three physical dimensions we usually see, and that gravity leaks away into the string theorists "extra" dimensions. Not extra dimensions like going to the land of oz, but rather tiny dimensions not observed on our size scales.

I don't know much about that, but these guys do.

http://www.sixtysymbols.com/videos/dimensions.htm

Electromagnetic attraction is so strong that for the most part all of the potential energy has been neutralized in matter by pairing off with opposite charges. It's already reached across the universe and found another particle to satisfy the attractive charge. Electrons and protons together make neutral matter. So except for on very small scales where the inverse square law comes to bear, these energies are almost exactly canceled out, leaving gravity to have it's way with matter on large scales.

Re: Why Sun and the planets are in the same plane?

Posted: Thu Jun 27, 2013 6:48 pm
by geo
Think of a massive cloud of gas and dust. It starts to coalesce and, due to its mass, to spin. The big blob in the center is large enough to eventually become the sun, spinning off outer remnants that likewise coalesce and become the planets. They're on the same plane because of that initial spin and its centrifugal force.

One of the blobs didn't quite have enough mass to coalesce into a planet. It broke up into smaller bits that became the asteroid belt between Mars and Jupiter. Likewise, the rings of Saturn and other giant planets are bits of a would-be moon that didn't have enough mass to coalesce in the orbit around these planets.

Mass determines gravity, not size. A body as massive as our sun creates a very strong gravitational pull, the earth much less so. But even a person has mass and so produces a very small gravitational pull. Two people walking past one another will have a very tiny attraction towards one another.

Re: Why Sun and the planets are in the same plane?

Posted: Thu Jun 27, 2013 7:13 pm
by ant
Haha, if i knew that, i would be a very famous man!
HAHA, you aren't God!
:wink:

Re: Why Sun and the planets are in the same plane?

Posted: Thu Jun 27, 2013 9:35 pm
by Robert Tulip
Bit like cars on the freeway. If you go any way except with the traffic you will crash.

A planet orbiting at an angle to the rest of the system is more likely to bang into something else as it crosses the line of the sun's equator.

Re: Why Sun and the planets are in the same plane?

Posted: Thu Jun 27, 2013 11:31 pm
by Interbane
A good thought experiment to help understand why is to think of a planet with two rings. One ring circles the equator, and the other is perpendicular, over the poles.

Now imagine the rocky, dusty ring material as it orbits the planet and intersects with the other ring. The stuff would collide at the intersection, and the rings would eventually dissipate, or more likely, merge into a singe ring.

Multiple orbital vectors are not sustainable unless they don't intersect. There could be a perpendicular orbiting body in our solar system as long as it didn't intersect with other bodies(over millions of years, it would need to be lucky to not collide even once).

Once the dust started spinning, the rotational plane was set and any objects on anomalous vectors were weeded out over time.

Re: Why Sun and the planets are in the same plane?

Posted: Fri Jun 28, 2013 1:31 am
by Rajesh
johnson1010 wrote: the overall motion of the nebula will be in the direction of the most particle’s initial inertia.

So basically, this is the factor which determines , in which direction and plane, the planets move around the sun in later stages !!