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Author Topic: Why do all of the planets in the solar system orbit in the same flat plane?  (Read 17378 times)

Offline moccacake

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Are the planets' orbits aligned horizontally just like they appear in book diagrams? Or each planets' orbits differ in inclination with relation to the earth's orbit?
« Last Edit: 25/12/2006 21:16:32 by chris »


 

Offline neilep

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Hi Moccacake,

I know Pluto has a real freaky orbit which brings it inside the orbit of Neptune for a while...mind you..Pluto is not a planet anymore is it ?

...and Uranus is on it's side....

..but I know this is not really what you asked.....

I am sure the answer will ensue.
 

Offline chris

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The answer is yes, the planets are all on the same plane. This is a legacy of the way the solar system formed in the first place, about 4.6 billion years ago.

Present models of the process suggest that a cloud of gas, which was called the solar nebula and was about 100 times the Earth-Sun distance across and 2-3 times the mass of the Sun, was jolted into action by a nearby exploding star (a supernova). This shockwave squeezed the nebula and caused it to begin to collapse under its own gravity. As it did so conservation of angular momentum resulted in a flat disc of spinning material, called a protoplanetary disc, that surrounded a developing "proto-star", the future Sun, at its centre.

The disc was effectively a proto-planetary soup of material, which slowly coaslesced to form initially planetessimals (baby planets) and then the larger individual planets we see today. The inner part of the disc, closest to the proto-star, were too hot for volatile and gaseous materials to condense, so the inner planets (Mercury, Venus, Earth, Mars) are all metal and silicate-rich "rocky" bodies.

Farther out, where the disc was cooler, lighter elements such as hydrogen could be captured and the gas giants Jupiter and Saturn formed. The asteroid field between Jupiter and Mars was the result of Jupiter's gravity. The massive planet prevented the debris in this part of the solar system from merging together to form an additional planet so it remains as an asteroid belt.

Since all of the planets formed from a disc of material they all lie on the same plane. They also all spin because the material that formed them was itself spinning. As the planets formed they also underwent a kind of cosmic gravitational billiards where resonanaces caused by their gravitational fields nudged everything around until it arrived in its present position. A space scientist called Adrian Brunini recently published a paper in Nature in which he modelled the early solar system and found that these resonances could account for the positions and eccentric orbits of some planets, and why Uranus is spinning on its side - it's been gravitationally tipped over during its development.

Chris
« Last Edit: 25/12/2006 21:15:20 by chris »
 

Offline DoctorBeaver

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Chris is right, unless you class Pluto as a planet. Its orbit is inclined to the plane of the rest of the planets. But Pluto may not have been formed the same way as the others. It's probably a stray rock that was captured by the sun's gravitational field.
 

Offline neilep

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Chris is right, unless you class Pluto as a planet. Its orbit is inclined to the plane of the rest of the planets. But Pluto may not have been formed the same way as the others. It's probably a stray rock that was captured by the sun's gravitational field.


Erreerrhmmmm !!!!

 

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