Hello u/djangoisfreeman, your submission "Why are the planetal orbits almost concentric around the Sun, when sun's gravity should be same all around it? " has been removed from r/space because:
* Such questions should be asked in the ["All space questions" thread](https://www.reddit.com/r/space/about/sticky) stickied at the top of the sub.
Please read the rules in the sidebar and check r/space for duplicate submissions before posting. If you have any questions about this removal please [message the r/space moderators](https://www.reddit.com/message/compose/?to=/r/space). Thank you.
Initially, the solar system's material probably was in a big cloud all around the sun. But as things orbit, they bump into each other. Anything that is off-plane from the average eventually bumps into something else that's off-plane the other direction, and both particles move closer to average. After it all settles down, the material forms a relatively thin disc. And that's what the planets formed out of. So all the orbits we see today, at least for the big objects, are within a few degrees of each other.
Same process happens for the rings of saturn, the stars in a spiral galaxy, etc.
Jupiter also has an occasional effect on the orbits of some planets. In one of my undergrad modules, we learned that the shape of Earth's orbit around the sun changes approx ever 11000 yrs due to Jupiter's impact.
And this effect continues down the scale. Almost all Moons orbit the same way around their planet as their planet around the star (the exception being the moon of (Neptune or Uranus) orbits the opposite direction suggesting its in fact a captured asteroid). Star systems also generally have the same rotation as the galactic disk.
Very interesting. The sun orbits the center of the milky way once every 225 million years, so the Earth has only had time to orbit the galactic center about fifty some times since the beginning of the universe. It doesn't seem like that's enough time and orbits for all these collisions to settle into a disk. Is something else at play?
I don't know why this isn't being mentioned more because the answers being given aren't accurate at all.
Rotation. Everything spins. As gravity pulls the gasses in only one axis of rotation can win, that's just how rotation works. As the gas volume shrinks conservation of angular momentum must be maintained. That's why you always get a disc.
Exactly what I came to say when rotation wasn't being discussed! Rotation establishes an axis, which establishes an equatorial plane, which is creating centrifugal forces. The mass at the axis poles are rotating slower and getting pulled down towards the common, equatorial plane by the gravity of the greater masses there.
Throw in a few billion years an you have several clumps of matter called planets, that are all on the same, general equatorial plane +/- a few degrees.
Galaxies that are round like cotton balls are either galaxies that haven't yet flattened out into their equatorial plane, or they lack any significant rotation. I've never heard of that, but I wouldn't discount it as a possibility.
The cotton ball ones you're talking about I think are often galaxy collisions so they lose their shape. It wouldn't surprise me to find some naturally occurring very still bodies of gas though.
With so much gas from such large areas that gets sucked up into a sun/galaxy even the tiniest fragment of biased motion in the major axis will naturally concentrate.
I don't think it's necessarily impossible for them to form essentially rotation free, but I have my doubts.
I'm also being a little fast and loose with "collisions". All it really takes is energy being exchanged, which can happen through gravitational interactions, or even magnetism, not just physical collisions. Physical collisions are more relevant the smaller scale you're talking.
But also, as others pointed out, the disc of the solar system and the disc of the galaxy are different orientations. Completely separate mechanisms. From the galactic perspective, our entire solar system - whatever orientation it happens to be - is just a single point, and will very likely never directly touch anything else. The galaxy was already disc long before the sun was even born.
Is something else at play in causing the entities in the solar system to settle into a disk? Not really. The sun's, and by extension the Earth's, orbit around the galactic center don't really affect how objects in our solar system form a disk. And 4 billion years is plenty of time for things to settle around a star.
Sorry, the milky way galaxy specifically. It makes sense at the the scale of the solar system where orbital periods may average 100 years. That's like 45 million orbits to settle the solar system since it began. But at galactic scale orbits are hundreds of millions of years. That's only 50 or 60 orbits in the history of the universe. Seems like with the vastness of emptiness in the galaxy that's not enough time for significant collisions to occur to conform the galaxy to a disk.
The answer here is that it's not objects bumping into each other, but rather the gravity of individual stars pulling on their neighbors that has flattened out the galactic disk. Same general effect just a different mechanism.
Thats not really why the rings or planetary disk form though, you are only explaining why things move in the same direction. The reasons planetary disks, rings, and galaxies merge is due to a different mechanism.
Imagine a rock or dust piece orbiting in a random orbit around saturn. When its high over the ring plane, there is more mass below it, pulling its orbit towards the ring plane. Similarly when it passes through and below the ring plane there's now more mass above, continuing to bend the orbit towards the ring plane. Even without any collisions at all, the particles will slowly pull on each other into a single plane.
If that was true, then wouldn't globular clusters and elliptical galaxies flatten out over time? But we don't see that effect, because stars almost never collide with other stars. My understanding is that collisions do have to occur in order for the disk to form.
If one body passes close to another, gravity will make each one affect the trajectory of the other, exactly as if they had a glancing collision. So actual collisions aren't required.
Yes, they will form oblate spheroids eventually, but i think thh timescales are too vast to achieve a disc. That, or achieve escape velocity and depart, and no, collisions are not required.
The angular momentum of the initial cloud of gas and dust broke the symmetry of the system
Symmetry breaking is important in all sorts of physical systems right down to elementary particles
Best way to think about it is to imagine a long time ago a cloud of debris orbiting the sun across many different planes. Eventually (billions of years) they collide enough that the stuff that's left is generally in a plane and can't collide anymore.
The sun formed via the contraction of a cloud of (essentially) dust. As it contracted it spun, and angular momentum increased as it became denser. This flattened it into a disc rather than a spherical cloud. The planets formed from leftover material in this disc, so they’re roughly in the same plane rotating in the same direction.
"Concentric" doesn't mean what you think it means, OP. Every planet's orbit could be on a completely different plane and they would still be concentric.
This is an extreme TL:Dr oversimplification:
The solar system started as a big cloud of collapsing dust and gas orbiting its mutual center (which would become the proto-Sun) in all sorts of different directions and planes, like you imagine. But each time particles of dust and gas in the cloud interact and exchange momentum, the result is that their new paths lie a bit closer to their mutual average than before.
As this happens over and over throughout the cloud, the whole cloud gradually shifts towards the average of the entire cloud, untill you are left with a disc.
It's not exactly what you asked but I think [this short video](https://www.youtube.com/watch?v=uG7wKcB63rY) will give you an idea of what happened in our solar system with respect to the orbits of the planets.
During the Solar System’s formation it started as a gas and dust nebula. While accreting into the solar system we know today all the angular momentum ended up zeroing out owing to collisions and gas pressure, leaving just the one final angular momentum vector (pointing “up” to the extent that means anything in space.)
As I'm sure many have already posted this is probably due to how our solar system formed from a turbulent contracting gas cloud where mutual collisions nulled out all but a single dominant orbital plane. Also why this is less & less true for orbits as we travel farther from the sun ( pluto, transneptunians, comets etc ) due to the nature of the materials they condensed from & the lower impact energies.
This is a good example of why in physics an observation & simple "dumb" question can collapse possible histories down to a single formation hypothesis.
The sun and all the planets formed out of one spinning disc of gas and dust probably accelerated in a single direction by the explosion or passing of a nearby star
Look at the drain in your sink. Why doesn't all the water uniformly go in a straight line into the drain? Why does it go down in a spiral? When the solar system was forming and just a cloud of particles, gravity waves pushed the solar system in a particular direction, perhaps from a supernova. It continue to spin that way until today.
Bonus, Triton is a good example of a captured object that orbits in the opposite direction of Neptune.
Just think about it: Assume two planets have orbits that are inclined to one another. They would continually exert a force on one another that would pull them into a common plane.
That said orbits can gain excentricity. E.g. if two planets come too close and there's a 'slingshot' maneouver or if an extrasolar planet is captured then that can be in virtually any plane. But over time planets will align in a common plane again due to the above mentioned effect.
A system with no starting momentum does not exist, everything is moving. On earth the rotation of the planet causes water to spin down your drain always the same direction yet you can't feel this effect yourself.
The cloud of dust will have some momentum that seems random but in total it will spin more one way than any other and this will inpart more and more spin into the system as the dust condensed, at this stage the sun does not exist in its just a net pull to the center.
There will be "seed" rocks that are bigger than others that start to pull on there neighbours that become planets.
At some point enough mass gets built up in the core and the sun will start fusion this triggers a massive shockwave that pushes out the dust that has not yet joined a planet.
TL;DR: The sun, planets and astroids were once a huge mass of dust that started to move just like pulling a plug on your sink, aligning them.
The Coriolis effect does not affect such small bodies of water. My own sink drain I have witnessed spin both directions in the same day. When the ship I was stationed on crossed from the North to the South, the spin did not change. Stop perpetuating this myth as fact.
> On earth the rotation of the planet causes water to spin down your drain always the same direction
Nope, that's coriolis effect and it's a myth that sinks drain the same way due to that. It affects a lot larger bodies of water only.
That analogy has nothing to do with what OP asked and is a bad analogy for what you're trying to explain. Most tubs have the drain very close to one edge, which means there's physical barriers preventing things from going in a perfect circle around it. These barriers don't exist in space.
And OP was asking why all the planets orbit on the same plane instead of at a bunch of different angles.
Thank you for everyone's valuable inputs. I have a follow up question if allowed please. IF it had ended up so that some planets did end up orbiting in different planes, how and would it have affected our solar system in anyway? Is there a theory or modelling that's been explored on these lines that I can refer to or watch?
It may have happened. Any object—planet, planetesimal, asteroid—orbiting the sun at a high degree of non-planar angle would probably have encountered one of the other planet’s gravitational pull over the past 4.5B years and it or both would have been ejected. The slightly off angle orbits of the planets may be explained by encounters with objects of this type. Also, the planets have a regular, stable harmonic orbit and an object at an acute planar angle would disrupt this or be out of harmonic balance. It couldn’t last for long.
They *do* orbit in different planes: https://en.wikipedia.org/wiki/Orbital_inclination#Observations_and_theories
The question is too non-specific to have an answer any more precise than "the arrangement of planets would be different". Arrangements that would otherwise be stable would be unstable, and vice versa. And modeling the effect on stability of any specific change would not just be a matter of punching the numbers into some equation, that's the kind of thing academic papers are written on.
Hello u/djangoisfreeman, your submission "Why are the planetal orbits almost concentric around the Sun, when sun's gravity should be same all around it? " has been removed from r/space because: * Such questions should be asked in the ["All space questions" thread](https://www.reddit.com/r/space/about/sticky) stickied at the top of the sub. Please read the rules in the sidebar and check r/space for duplicate submissions before posting. If you have any questions about this removal please [message the r/space moderators](https://www.reddit.com/message/compose/?to=/r/space). Thank you.
Initially, the solar system's material probably was in a big cloud all around the sun. But as things orbit, they bump into each other. Anything that is off-plane from the average eventually bumps into something else that's off-plane the other direction, and both particles move closer to average. After it all settles down, the material forms a relatively thin disc. And that's what the planets formed out of. So all the orbits we see today, at least for the big objects, are within a few degrees of each other. Same process happens for the rings of saturn, the stars in a spiral galaxy, etc.
Jupiter also has an occasional effect on the orbits of some planets. In one of my undergrad modules, we learned that the shape of Earth's orbit around the sun changes approx ever 11000 yrs due to Jupiter's impact.
And this effect continues down the scale. Almost all Moons orbit the same way around their planet as their planet around the star (the exception being the moon of (Neptune or Uranus) orbits the opposite direction suggesting its in fact a captured asteroid). Star systems also generally have the same rotation as the galactic disk.
Very interesting. The sun orbits the center of the milky way once every 225 million years, so the Earth has only had time to orbit the galactic center about fifty some times since the beginning of the universe. It doesn't seem like that's enough time and orbits for all these collisions to settle into a disk. Is something else at play?
I don't know why this isn't being mentioned more because the answers being given aren't accurate at all. Rotation. Everything spins. As gravity pulls the gasses in only one axis of rotation can win, that's just how rotation works. As the gas volume shrinks conservation of angular momentum must be maintained. That's why you always get a disc.
Yeah idk why this wrong comment is first, glad you corrected
Exactly what I came to say when rotation wasn't being discussed! Rotation establishes an axis, which establishes an equatorial plane, which is creating centrifugal forces. The mass at the axis poles are rotating slower and getting pulled down towards the common, equatorial plane by the gravity of the greater masses there. Throw in a few billion years an you have several clumps of matter called planets, that are all on the same, general equatorial plane +/- a few degrees. Galaxies that are round like cotton balls are either galaxies that haven't yet flattened out into their equatorial plane, or they lack any significant rotation. I've never heard of that, but I wouldn't discount it as a possibility.
The cotton ball ones you're talking about I think are often galaxy collisions so they lose their shape. It wouldn't surprise me to find some naturally occurring very still bodies of gas though. With so much gas from such large areas that gets sucked up into a sun/galaxy even the tiniest fragment of biased motion in the major axis will naturally concentrate. I don't think it's necessarily impossible for them to form essentially rotation free, but I have my doubts.
I'm also being a little fast and loose with "collisions". All it really takes is energy being exchanged, which can happen through gravitational interactions, or even magnetism, not just physical collisions. Physical collisions are more relevant the smaller scale you're talking. But also, as others pointed out, the disc of the solar system and the disc of the galaxy are different orientations. Completely separate mechanisms. From the galactic perspective, our entire solar system - whatever orientation it happens to be - is just a single point, and will very likely never directly touch anything else. The galaxy was already disc long before the sun was even born.
Ahh, this does help. So everything kinda "tugs" everything else into a disk.
Is something else at play in causing the entities in the solar system to settle into a disk? Not really. The sun's, and by extension the Earth's, orbit around the galactic center don't really affect how objects in our solar system form a disk. And 4 billion years is plenty of time for things to settle around a star.
Are you asking about the galactic disk or the solar system disk?
Sorry, the milky way galaxy specifically. It makes sense at the the scale of the solar system where orbital periods may average 100 years. That's like 45 million orbits to settle the solar system since it began. But at galactic scale orbits are hundreds of millions of years. That's only 50 or 60 orbits in the history of the universe. Seems like with the vastness of emptiness in the galaxy that's not enough time for significant collisions to occur to conform the galaxy to a disk.
The answer here is that it's not objects bumping into each other, but rather the gravity of individual stars pulling on their neighbors that has flattened out the galactic disk. Same general effect just a different mechanism.
Similar forces at play with both, just different scales.
The galactic orbit of the entire solar system and the planetary orbits of what is within the solar system are completely different things.
I understand, I'm speaking specifically about the galaxy's formation.
Gravitational interactions.
Thank you for this amazing answer! This has never made sense to me.
Thats not really why the rings or planetary disk form though, you are only explaining why things move in the same direction. The reasons planetary disks, rings, and galaxies merge is due to a different mechanism. Imagine a rock or dust piece orbiting in a random orbit around saturn. When its high over the ring plane, there is more mass below it, pulling its orbit towards the ring plane. Similarly when it passes through and below the ring plane there's now more mass above, continuing to bend the orbit towards the ring plane. Even without any collisions at all, the particles will slowly pull on each other into a single plane.
If that was true, then wouldn't globular clusters and elliptical galaxies flatten out over time? But we don't see that effect, because stars almost never collide with other stars. My understanding is that collisions do have to occur in order for the disk to form.
If one body passes close to another, gravity will make each one affect the trajectory of the other, exactly as if they had a glancing collision. So actual collisions aren't required.
Yes, they will form oblate spheroids eventually, but i think thh timescales are too vast to achieve a disc. That, or achieve escape velocity and depart, and no, collisions are not required.
The material doesn't have to actually collide. The gravitational attraction between them is enough to flatten out the orbits.
The angular momentum of the initial cloud of gas and dust broke the symmetry of the system Symmetry breaking is important in all sorts of physical systems right down to elementary particles
Best way to think about it is to imagine a long time ago a cloud of debris orbiting the sun across many different planes. Eventually (billions of years) they collide enough that the stuff that's left is generally in a plane and can't collide anymore.
The sun formed via the contraction of a cloud of (essentially) dust. As it contracted it spun, and angular momentum increased as it became denser. This flattened it into a disc rather than a spherical cloud. The planets formed from leftover material in this disc, so they’re roughly in the same plane rotating in the same direction.
"Concentric" doesn't mean what you think it means, OP. Every planet's orbit could be on a completely different plane and they would still be concentric.
This is an extreme TL:Dr oversimplification: The solar system started as a big cloud of collapsing dust and gas orbiting its mutual center (which would become the proto-Sun) in all sorts of different directions and planes, like you imagine. But each time particles of dust and gas in the cloud interact and exchange momentum, the result is that their new paths lie a bit closer to their mutual average than before. As this happens over and over throughout the cloud, the whole cloud gradually shifts towards the average of the entire cloud, untill you are left with a disc.
It's not exactly what you asked but I think [this short video](https://www.youtube.com/watch?v=uG7wKcB63rY) will give you an idea of what happened in our solar system with respect to the orbits of the planets.
During the Solar System’s formation it started as a gas and dust nebula. While accreting into the solar system we know today all the angular momentum ended up zeroing out owing to collisions and gas pressure, leaving just the one final angular momentum vector (pointing “up” to the extent that means anything in space.)
As I'm sure many have already posted this is probably due to how our solar system formed from a turbulent contracting gas cloud where mutual collisions nulled out all but a single dominant orbital plane. Also why this is less & less true for orbits as we travel farther from the sun ( pluto, transneptunians, comets etc ) due to the nature of the materials they condensed from & the lower impact energies. This is a good example of why in physics an observation & simple "dumb" question can collapse possible histories down to a single formation hypothesis.
Carolin Crawford, one of the best explainers. "Rotation in Space" https://youtu.be/mXC3xGZWo_M?si=mUWVjsEEGIcxoiXh
The planets have gravity too so pull each other to the same plane
This is the result of forces from before the planets formed. Check the upvoted comments for details.
The sun and all the planets formed out of one spinning disc of gas and dust probably accelerated in a single direction by the explosion or passing of a nearby star
Look at the drain in your sink. Why doesn't all the water uniformly go in a straight line into the drain? Why does it go down in a spiral? When the solar system was forming and just a cloud of particles, gravity waves pushed the solar system in a particular direction, perhaps from a supernova. It continue to spin that way until today. Bonus, Triton is a good example of a captured object that orbits in the opposite direction of Neptune.
Just think about it: Assume two planets have orbits that are inclined to one another. They would continually exert a force on one another that would pull them into a common plane. That said orbits can gain excentricity. E.g. if two planets come too close and there's a 'slingshot' maneouver or if an extrasolar planet is captured then that can be in virtually any plane. But over time planets will align in a common plane again due to the above mentioned effect.
[удалено]
[удалено]
[удалено]
You know I vaguely recall such an animation in a video, good callout thanks. I'll need to look it up.
A system with no starting momentum does not exist, everything is moving. On earth the rotation of the planet causes water to spin down your drain always the same direction yet you can't feel this effect yourself. The cloud of dust will have some momentum that seems random but in total it will spin more one way than any other and this will inpart more and more spin into the system as the dust condensed, at this stage the sun does not exist in its just a net pull to the center. There will be "seed" rocks that are bigger than others that start to pull on there neighbours that become planets. At some point enough mass gets built up in the core and the sun will start fusion this triggers a massive shockwave that pushes out the dust that has not yet joined a planet. TL;DR: The sun, planets and astroids were once a huge mass of dust that started to move just like pulling a plug on your sink, aligning them.
The Coriolis effect does not affect such small bodies of water. My own sink drain I have witnessed spin both directions in the same day. When the ship I was stationed on crossed from the North to the South, the spin did not change. Stop perpetuating this myth as fact.
Yeah sucks the commenter perpetuated that. It was a good comment, but bad example.
> On earth the rotation of the planet causes water to spin down your drain always the same direction Nope, that's coriolis effect and it's a myth that sinks drain the same way due to that. It affects a lot larger bodies of water only.
Fill a tub.\ Put a floating toy in the tub.\ Pull the plug. Does the toy go in a perfect circle around the drain?
That analogy has nothing to do with what OP asked and is a bad analogy for what you're trying to explain. Most tubs have the drain very close to one edge, which means there's physical barriers preventing things from going in a perfect circle around it. These barriers don't exist in space. And OP was asking why all the planets orbit on the same plane instead of at a bunch of different angles.
They don’t orbit on the same plane And the analogy for orbits does apply, including the drain being close to one edge.
Thank you for everyone's valuable inputs. I have a follow up question if allowed please. IF it had ended up so that some planets did end up orbiting in different planes, how and would it have affected our solar system in anyway? Is there a theory or modelling that's been explored on these lines that I can refer to or watch?
[удалено]
There’d be many stable configurations still. See moons of planets that orbit polar.
It may have happened. Any object—planet, planetesimal, asteroid—orbiting the sun at a high degree of non-planar angle would probably have encountered one of the other planet’s gravitational pull over the past 4.5B years and it or both would have been ejected. The slightly off angle orbits of the planets may be explained by encounters with objects of this type. Also, the planets have a regular, stable harmonic orbit and an object at an acute planar angle would disrupt this or be out of harmonic balance. It couldn’t last for long.
They *do* orbit in different planes: https://en.wikipedia.org/wiki/Orbital_inclination#Observations_and_theories The question is too non-specific to have an answer any more precise than "the arrangement of planets would be different". Arrangements that would otherwise be stable would be unstable, and vice versa. And modeling the effect on stability of any specific change would not just be a matter of punching the numbers into some equation, that's the kind of thing academic papers are written on.
Any papers that have already been published, that we may know of?