Planetary Orbits

[Thunderbird4!]

This probobly has an extremely simple answer but it's been bothering me for a while...

Why is it that all 8 planets' orbits are on a (nearly) level plane with each other, while we find that comets and Pluto, amongst other non-planetary ojects, do not remain on this level plane?

Thanks.

[miles01110]

Nobody really knows for sure, but I think the leading theory is that the solar system started out as a disk of gas that gradually coalesced into the planets we know and love. Many think Pluto is an extra-solar object that somehow got captured by the sun's (or Neptune's) gravity.

Comets are very extra-solar objects, and were formed in deep space and their orbits were influenced by the sun's gravity, which means they probably aren't orbiting on the orbital plane.

[Zohar]

It's not very simple at all. There are no conclusive theories regarding the creation of solar systems.

There were some theories before the discovery of other planetary systems, but those theories failed once we found solar systems with Jupiter-sized planets closer to their sun than our Earth's orbit - it just couldn't exist according to the theory (in our solar system, the inner planets are all solid, the outer planets are all gas giants, with the exception of Pluto).

Most attempts at a theory begin with a gas disk of some sort, which seems natural - all planets revolve around the sun in the same direction (the gas disk's supposedly) and around themselves in the same direction (except for one of them, I think Uranus but I'm not sure).

Anything that came into the solar system at a later time doesn't necessarily move in the same plane as the rest of it.

[oblivimous]

If the solar system condensed from a disk, where did the disk come from?

How do you get from the individual, spherelike, chaotic remnants of previous supernovae to an orderly rotating disk?

[markkat]

If the solar system condensed from a disk, where did the disk come from?

How do you get from the individual, spherelike, chaotic remnants of previous supernovae to an orderly rotating disk?

Simple mechanics leads any rotating sphere to flatten to a disk. The parts nearest the equator experience the greatest acceleration outward. -Each of the planets are actually a bit wider in the middle, even the Earth. Saturn is obviously so.

I should also add that any constricting mass will tend to rotate, and that the rotation accelerates as its radius decreases. -Think of the figure skater analogy.

[oblivimous]

Simple mechanics leads any rotating sphere to flatten to a disk.

How do we get from chaotic supernovae remnants to a rotating sphere? What causes rotation to begin? What determines the axis and direction of rotation?

[markkat]

Its nearly impossible for rotation not to begin. Any angular momentum due to asymmetry in the collapse (or prior expanse) would lead to it.

As the gravitational collapse progresses, this rotation is amplified by the conservation of angular momentum. -The direction of the rotation is arbitrary, and based upon these asymmetries. That is, excluding any possible outside influences (a passing galaxy, etc.).

[Yakk]

Take a big pile of stuff moving randomly.

Now have a clump, placed randomly.

This clump causes some of the nearby stuff to fall inwards towards it (gravity). Each bit that is captured has a random original movement.

The total angular velocity of the resulting object is the sum of the angular velocities of the things that contributed.

A small imbalance in the contributing stuffs' can result in a large amount of angular momentum -- this is the "pull your arms in when you spin, and you spin faster" effect, but on a really really huge scale.

The collapse is slowed by the heating of the things that collapse. This heat creates a resistence to the collapse (a pressure that opposes the collapse). This heat bleeds off (thermodynamics) because it is hotter than the surroundings. As the clump cools, it collapses more. It also becomes better at not losing the matter it sucks in, which makes it's net growth faster.

The momentum of the particles gets passed around via collisions and photons. This turns the rotating sphere into a rotating disc over time. Sub-clumps gather and suck in matter locally.

In the center of all of this is a mega-clump. It passes a critical threshold, and gravity overcomes the light pressure, and it falls inward. Heat increases as gravitational potential energy is converted into heat, but the power of gravity is stringer than the heat pressure.

Then, ignition! The center gets hot enough that the hydrogen and helium fuse. This creates a new source of heat, and the star is born. The new light pressure fights against gravity.

The newly ignited sun pushes against the cloud surrounding the star. Loos dust gets pushed away, while larger clumps survive. The larger clumps collide with each other and tug at each other: those that survive form planets.

...

That sound like a "detail-agnostic" narrative for the birth of a solar system?

[caliman83]

Ok so lets say you have the sun. and a disk of gas's, rock and other debre spining around it. How then dose that turn in to indvidule spheres each with there own uniqe orbit(the planets orbits are all at slightly diffrent orbits)
the 2nd problem is all the the planets should be rotating direction however Venus, Uranus, spin backwerds.
all 72 moons should spin the same direction as there planets however at least 8 spin backwerds (jupiter and saturn have moons spin in both diretions)

Pluse if the planets came out of the sun wich is 98% hydrogen and helium then shouldnt the inner planets be composed of much of the same materal. they dont.
there must be an explanation to all this but I dont see hoe the spinning disk theory makes any since.

[Thunderbird4!]

the 2nd problem is all the the planets should be rotating direction however Venus, Uranus, spin backwerds.

Pluse if the planets came out of the sun wich is 98% hydrogen and helium then shouldnt the inner planets be composed of much of the same materal. they dont.
there must be an explanation to all this but I dont see hoe the spinning disk theory makes any since.

I can answer this one, and correct that first bit. Venus rotates in the opposite direction, Uranus rotates at a right angle to the other planets (ie it rotates upto down where others go left to right)

The planets didn't come out of hte sun, they came from objects in interstellar space that were captured by the sun's gravity and the aforementioned disk wasn't just made out of gas, it was made out of rocks and other solid materials that would keep colliding and colliding until it grew large enough to dominate its orbit and cleared it of other things.

[DonChubby]

Ok so lets say you have the sun. and a disk of gas's, rock and other debre spining around it. How then dose that turn in to indvidule spheres each with there own uniqe orbit(the planets orbits are all at slightly diffrent orbits)
the 2nd problem is all the the planets should be rotating direction however Venus, Uranus, spin backwerds.
all 72 moons should spin the same direction as there planets however at least 8 spin backwerds (jupiter and saturn have moons spin in both diretions)

Pluse if the planets came out of the sun wich is 98% hydrogen and helium then shouldnt the inner planets be composed of much of the same materal. they dont.
there must be an explanation to all this but I dont see hoe the spinning disk theory makes any since.

Mkay.
The disks turn into individual spheres because of gravity, the matter of the disks attracts the other matter(does that make sense?), which in turn attracts more matter until you have a nice little sphere.
As for the second question, Yakk had a rather good explanation for that.
And thirdly, all the matter in this solar system doesn't necessarily come from OUR sun, it's matter flying around in space, but the solar system is certainly made out of a lot of "stardust", from exploding supernovas.

-EDIT-
Argh, beat to it, and by an even better explanation too.

[caliman83]

Makes since. thats one of those things Ive been meaning to research but I never get the time.

[DonChubby]

*Offtopic*
Oh, it would be nice if you posted in the introduction thread Caliman.

[Yakk]

He's a solar system spam synthetic!

[niko7865]

Don't listen to them, I have yet to post in the intro thread...


Soon the forum will be spammed as it has never been spammed before!! Muahahahaha!!