Planet Orbit?

Question

Disregarding Pluto, because it is no longer a planet.

Why does every planet in out solar system have an orbit that is relatively in a straight line in comparison to other planets? All of our palnets are in a horizontal orbit as opposed to a few going in a vertical orbit.

Answer 1

It's called the plane of the ecliptic. It's actually the case that many if not all of the planets orbit slightly off of the actual plane. but it has to do with how star systems form.

The sun started out as a big cloud of gas and dust left over from the titanic explosion of some previous super-giant star or stars.

Gravity started to pull dust and gas towards the the center of this cloud and eventually that center cloud became pretty dense - perhaps like a planet which was just orbiting and which continued to accumulate more matter more hydrogen more helium etc.

When a star is born, it shoots out giant magnetic force waves from the poles (like a regular magnet) these force lines would tend to clear matter away from the poles.

For some time now the rest of the cloud has started to move first randomly but then started to circulate around and as stuff tends to circulate it tends to get flatter - Think of what happens to a pizza pie when it's tossed in the air,

As the planets formed up by exerting gravity on their local areas there were probably dozens of planets in our early solar system which smashed into one another. The early solar system was definitely not a safe place, the gas giants Saturn and Jupiter in particular dominated the solar system and threw some junk in towards the sun and some stuff out towards the other outer planets.

Farther out there is less speed relative to the sun so there is less tendency to straighten up and fly along the ecliptic. Pluto and the other outer small planets (as there will be several dozens or hundreds eventually discovered - but most not as large as Pluto).

these form the Kuiper belt which is like a donut shaped ring of ice and rock and dust left over from this active early solar system.

Far beyond that is the Oort cloud which is icy cometary and dust material, This cloud is still in a sphericial shape from when the blast of the Sun's birth affected this area.

http://en.wikipedia.org/wiki/Inclination#Orbits

For a good show of other star systems that we know about check out the links below.

Answer 2

There is actually a pretty good deal of variance.

But, they are all pretty close, relative to the same plane, because when the Sun was in formation, there was a bunch of excess material and it was all swirling around the protostar in the center.

Centrifigul force means that this spinning will tend to force this matter into a disk, that disk is called the protoplanetary disk and is the source of the planets.

The matter in this disk bumped and colided, chunks getting bigger and bigger, and as they got bigger started to attract more material because of gravity, until they are finally the planets we recognise today.

Some of this matierial is still out there, in the form of meteors and planetoids like Pluto. Other parts were flung out by out larger cousins like Jupiter and Saturn and form things much further out than Pluto like the Oort Cloud.

Occasional disturbances of this cloud send these into our nearer solar system and they become comets.

It has been suggested that our Sun has a dark companion star,(Called a Brown Dwarf; think Jupiter but bigger) with a distant orbit that every five thousand years or so disturbs a great many of these Oort cloud objects and the result is a hail of comets into the planetary portion of the solar system, which in turn disturb a multitude of meteors which rain on the inner planets. Which would explain why there seems to be a cycle of large planetary impacts and mass extinctions around every five thousand years.

They refer to the dark star as Nemisis and it's refered to as the Nemisis Extinction Theory.

I tend to buy into this argument just because I think it sounds cool.

Answer 3

Some of the moons of Jupiter and Saturn are quite large and have atmospheres and perhaps ecosystems. But if it orbits a planet, it's a moon, not a planet.

Answer 4

It is believed that everything in the solar system coalesced (condensed) out of a relatively flat spinning disk of matter so everything would be in the same plane.