Jump to content


Why is the Solar system flat?

Recommended Posts


I was wondering why the solar system is in one plane. I know the orbits of the planets are slightly different, but why aren’t the orbits random (not all in the same plane). We can see this pattern in the rings of Saturn and the moons of Jupiter. Is there any evidence of the shape of other solar systems?

I suppose it must be something to do with the shape of the dust cloud that the planets formed from but how did this flat plane of dust form?

I may be barking up the wrong tree here but I’d like to hear what you think?

Link to comment
Share on other sites

The sun formed first, and once nuclear fusion commenced, the pressures from the solar wind eased the rest of the accretion disc outwards, where the planets began to form. Angular momentum has a role in the orbital planes, but it will take someone with more understanding of the process to explain it better.

The Kuiper Belt, which is home to the rubble left over, and lies way out beyond the orbits of Neptune and Pluto, is also in the same plane as the Solar System.

Way beyond that, and at an enormous distance, is the Oort Cloud, but that is a spherical shell of material, and could be regarded as the egg shell of the Solar System.

Sometimes, the gravitational effects resulting from the galactic rotation, could nudge a comet in towards the sun, and as it may not enter in the plane of the solar system, it makes them dangerous from a detection point of view, as they can appear from any direction, and we don't have eyes to watch everywhere.

If I'm not mistaken, comets Hyukutake, and Hale Bopp entered our system at about 90 degrees to the plane of the solar system.

I'm happy to be corrected if I'm wrong on any of these points.:)


Edited by barkis
Link to comment
Share on other sites

Scientists think that the solar system formed out of a spinning cloud of hydrogen and helium gas.

Because the cloud was spinning, it flattened into a frisbee shape, just like a ball of pizza dough becomes flat when a chef spins it in the air. The planets and the sun started to form after the cloud of gas became a flat disk.

As the cloud flattened, the gaseous material inside was forced to begin changing into solid form. These little particles of solid material were soft and sticky, and further clumped together to form larger balls of solid material whenever they touched each other, Eventually only a few large clumps of this material remained in the forming solar system, and they became the core of sun and planets

Link to comment
Share on other sites

Because it is spinning.

The axis of rotation is defined and things spin around that. If it didn't spin then no planets.

They would have long go been gravitationally dragged into the sun.

Link to comment
Share on other sites

Just to add a bit more to the "it's about momentum" style comments...

Take a large clound of cloud and gas. For sake of argument, let's say it is spinning very slowly (most things in space are for various reasons). Gravity within the cloud over millions of years attracts material to the centre. Angular momentum must always be maintained, so the spin accelerates as the mass moves towards the centre (think of a spinning ice-skater - with her arms out she will spin quite slowly, speeding up a lot as she draws her arms in towards her body).

At this stage, the mass of the central part of the cloud is increasing and gravity starting to make material from all over the cloud fall towards the centre. Anything in the central plane (perpendicular to the axis of rotation, passing through the centre of mass) will begin to orbit the cental mass. Now consider material that was near the "top" of the cloud - this is being pulled towards the central mass but is not rotating around it so it gradually spirals in.

Eventually, all the material that is signifacntly off the central plane spirals into the central mass which goes on to form a star. As others have said, the material in the central plane coalesces and forms planets, asteroids and so on.

Exaclty how the Oort cloud formed or what shape it takes (uniform spherical shell or doughnut shaped?) is not clearly understood but material falling in towards the central mass and just missing due to its initial spin could be thrown into a highly eccentric orbit at any angle to the central plane or even just expelled; anything sufficiently far out may just stay there in a very slow orbit.

Hope this helps!


Link to comment
Share on other sites

Yep, you can watch albeit slowly the rotation of the sun by following the sunspots move across the face of the sun(using a filter).

More inforation can be found here >http://en.wikipedia.org/wiki/Solar_rotation< the sun spins every 26ish days.



Hmm... is there a point of reference? How do you tell that the perceived movement of the sunspots isn't due to the movement of the Earth around the sun?

Note i don't doubt what you're saying, i just seek to understand it :)

Link to comment
Share on other sites

Hmm... is there a point of reference? How do you tell that the perceived movement of the sunspots isn't due to the movement of the Earth around the sun?

Note i don't doubt what you're saying, i just seek to understand it :)

The sun rotates about every 24 days at the equator, though it varies with latitude. As a result, you can see sunspots, etc. moving across the solar disk far faster than if it was down to the Earth's orbit about a stationary sun. This 24 days isn't disagreeing with Ant's 26 days - the Earth is orbiting the sun in the same direction as the sun is spinning (as you would expect); this extends the amount of time any given feature is visible on the surface giving an apparent 26 day rotation time.

In fact, Pete's (Starman) joint winner of this week's Picture of the Week is an excellent illustration of this: http://stargazerslounge.com/picture-week-competitions/143868-pow-29-05-11-a.html

Edited by jamespels
edited cos I keep making mistakes!
Link to comment
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now

  • Create New...

Important Information

We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue. By using this site, you agree to our Terms of Use.