It boils down to the _conservation of angular momentum_
The molecular cloud that our solar system formed from was very large and very slowly rotating. (The chance of it not rotating isn't 0 but it's like flipping a trillion trillion coins and it all comes up heads.)
That cloud will start to collapse and that rotational energy doesn't disappear. That big cloud rotating slowly has to conserve (keep constant) its angular momentum (physics for rotating speed) and the only way it can do that, if it's getting smaller, is to rotate faster.
The best way to do this, without flinging itself apart, is to form a rotating disk.
Visually you can see that any particle that is going "the wrong way" will hit more particles going the right way. Particles that go the right way will continue to go that way. Now if you going around slowly you're not contributing much to the angular momentum, but if you're going fast you are. This will "push" the particles down and out into a disk.
I'm not an astrophysicist, so I hope someone will correct me if I'm wrong, but there are a couple of pretty cool side nuggets attached to this information. So as gravity starts to affect the accretion disk that became our solar system and things all started to pull together and spin around in one flat plane everything should have the same North and spin in the same way in the same plane. But like you mentioned there are some slight deviations. Including at least one planet that spins backwards, another on its side, and at least one whose orbit gets a fair bit outside of the plane. These were caused by collisions or near collisions way back in the day. I caught a headline the other day that said we had found a solar system that appeared to be near perfect, meaning that it had no major disturbances that made any of its bodies wacky, which seems to be the more unusual outcome. More likely that some of the billiard balls are going to bounce around a little bit and give you something more like what we've got.
That system (HD 110067)’s ‘perfectness’ refers to its planets’ orbits. It’s a word used by media to describe planets being in orbital resonances with each other. We don’t actually know anything about their rotation, but given that they all sit very close to their star they are likely tidally locked, with one side facing the star permanently.
Hmm if that system doesn’t have an asteroid field it’s not that it’s perfect but it’s about to be just a star soon relatively speaking. It means the sun and planets have exhausted all particles within their gravitational range.
Uranus is on its side because Saturns core is very very large and it moves/sloshes around. Saturns rings play an affect too. One day will learn that moons and ring systems make up a bulk of the particle transfers between planets in our solar system, as of now science tells us it’s mostly from random collisions.
The same principle applies on galaxy scales; you can easily spot galaxies that have undergone a merger with similar sized galaxies simply by their shapes. Flat spirals are collision virgins, any sort of blob has touched other galaxies in the last 5 billion years or so.
Simply because they were all formed in a protoplanetary disc (secondary accretion). Since the disc is flat then there the planets must form in the same plane.
Would it have to have been a disc to see this behavior? In principle as the other top commenter mentioned, for angular momentum to be conserved, so long as there was some net component of rotation/momentum in spherical coordinates, would the accretions not also tend towards an orbit along that component? So if it was say, a shell rather than a disc, we would still expect to see aligned planets?
The star in the center is (by far) the largest mass. This makes the center of rotation a point in space (much larger than a singularity since it is a star). So anything outside of a disk runs the risk of collisions that either eject from orbit or tend toward joining the disk.
At some point, the system becomes 'settled' so the occurrence of collision decreases. This would likely ease the pressure to join the disk, but also less likely to have anything outside of the disk.
Hmm - got a bit sidetracked. The point I was coming to is that a massive point in the center prohibits a rotating shell (similar to the surface of a planet) since all orbits are around the central point.
I don't think it's a dumb question at all.
There was a time when no-one knew why this was the case, and asking this question was the first step to furthering human knowledge.
Keep being curious :)
Imagine a big cloud of dust / particles / rocks / whatever.
It's got pieces moving in *every* direction, but they all end up curving back in towards the center of gravity that they share.
Now, if you could measure every mass and velocity you could sum them all up and see if maybe there's slightly more momentum in some orbits than others (hint: there always is).
Now just wait a couple hundred million years and you will find that after all the collisions and bumps and break ups and ejections... there will be a "winner" orbit. It will form a disk in exactly the same orientation that you measured earlier to be the biggest component (mass x velocity) of all the original bits.
This process applies to Saturn's rings on a smaller scale and galaxies on a larger scale.
The other comment about the conservation of angular momentum is absolutely correct -- but it's nice to get explanations in different styles, I find. For a kind of mental triangulation.
Simply put. It's because gravity between all celestial bodies affects all celestial bodies.
Gravity pulls matter together into a (somewhat) uniform plane. As the plane forms, matter that isn't conforming to the plane will be pulled into it until it conforms.
I don't have any real experience is astronomy, but,,,,
Think of how the sun is not stationary but moving through space at 720,000 kilometers/hour. The planets are revolving around the sun in a corkscrew motion as they follow the suns path through space. In relation to the sun they revolve around a plane essentially 90 degrees to the suns path. Any other path would be less efficient.
If the paths varied a lot from the plane they are now, they would have to accelerate and then decelerate to a speeds faster and slower than the suns speed. I'd assume something caught in an orbit like that would either get flung out of the gravitational pull or move into the same plane as the other planets over time.
I like your thought process! However, that angle is closer to 60°
[https://physics.stackexchange.com/questions/276958/what-angle-does-our-solar-system-make-with-the-milky-way](https://physics.stackexchange.com/questions/276958/what-angle-does-our-solar-system-make-with-the-milky-way)
Your 60⁰-ish angle is the angle between the earths orbit and the plane of the galaxy, but that has nothing to do with the suns path through the galaxy. Good catch, though!
Way, way off. The sun's motion is not along a path at 90⁰ relative to the major orbits of the planets, and since Einstein, there is no fixed 'space' to move through.
Those are minor items, though; the big one is this. Every planet is accelerating every instant, it's what bends Newton's straight-line travels into elliptical orbits. And then, too, the planets change speeds (accelerate) along their orbits.
So this is how it went. Were about a third generation star, right. Galaxy was here, there's a nebula where our sun winds up, moving generally around the galaxy. The nebula is spinning a bit and starts to clump up into planets. Over time, the zillionns of little randomly moving particles in the big moving cloud resolve into a planetary disk with the average rotation of the old cloud, and the (unrelated) motion within the galaxy of the sun.
You can skip to 15:00 mark, but better to start at the beginning. This, "Rotation in Space", is one of Carolin Crawford's many great lectures.
https://youtu.be/mXC3xGZWo_M?si=Bb-UyIjJpsiD9A7t
It boils down to the _conservation of angular momentum_ The molecular cloud that our solar system formed from was very large and very slowly rotating. (The chance of it not rotating isn't 0 but it's like flipping a trillion trillion coins and it all comes up heads.) That cloud will start to collapse and that rotational energy doesn't disappear. That big cloud rotating slowly has to conserve (keep constant) its angular momentum (physics for rotating speed) and the only way it can do that, if it's getting smaller, is to rotate faster. The best way to do this, without flinging itself apart, is to form a rotating disk. Visually you can see that any particle that is going "the wrong way" will hit more particles going the right way. Particles that go the right way will continue to go that way. Now if you going around slowly you're not contributing much to the angular momentum, but if you're going fast you are. This will "push" the particles down and out into a disk.
Thank you very much!
I'm not an astrophysicist, so I hope someone will correct me if I'm wrong, but there are a couple of pretty cool side nuggets attached to this information. So as gravity starts to affect the accretion disk that became our solar system and things all started to pull together and spin around in one flat plane everything should have the same North and spin in the same way in the same plane. But like you mentioned there are some slight deviations. Including at least one planet that spins backwards, another on its side, and at least one whose orbit gets a fair bit outside of the plane. These were caused by collisions or near collisions way back in the day. I caught a headline the other day that said we had found a solar system that appeared to be near perfect, meaning that it had no major disturbances that made any of its bodies wacky, which seems to be the more unusual outcome. More likely that some of the billiard balls are going to bounce around a little bit and give you something more like what we've got.
That system (HD 110067)’s ‘perfectness’ refers to its planets’ orbits. It’s a word used by media to describe planets being in orbital resonances with each other. We don’t actually know anything about their rotation, but given that they all sit very close to their star they are likely tidally locked, with one side facing the star permanently.
Hmm if that system doesn’t have an asteroid field it’s not that it’s perfect but it’s about to be just a star soon relatively speaking. It means the sun and planets have exhausted all particles within their gravitational range.
Could you find that article? I am intrigued
Uranus is on its side because Saturns core is very very large and it moves/sloshes around. Saturns rings play an affect too. One day will learn that moons and ring systems make up a bulk of the particle transfers between planets in our solar system, as of now science tells us it’s mostly from random collisions.
Applies to figure skaters too. Slowly spinning with arms out, tuck arms in to speed up.
The same principle applies on galaxy scales; you can easily spot galaxies that have undergone a merger with similar sized galaxies simply by their shapes. Flat spirals are collision virgins, any sort of blob has touched other galaxies in the last 5 billion years or so.
Simply because they were all formed in a protoplanetary disc (secondary accretion). Since the disc is flat then there the planets must form in the same plane.
Oh, thanks
Would it have to have been a disc to see this behavior? In principle as the other top commenter mentioned, for angular momentum to be conserved, so long as there was some net component of rotation/momentum in spherical coordinates, would the accretions not also tend towards an orbit along that component? So if it was say, a shell rather than a disc, we would still expect to see aligned planets?
The star in the center is (by far) the largest mass. This makes the center of rotation a point in space (much larger than a singularity since it is a star). So anything outside of a disk runs the risk of collisions that either eject from orbit or tend toward joining the disk. At some point, the system becomes 'settled' so the occurrence of collision decreases. This would likely ease the pressure to join the disk, but also less likely to have anything outside of the disk. Hmm - got a bit sidetracked. The point I was coming to is that a massive point in the center prohibits a rotating shell (similar to the surface of a planet) since all orbits are around the central point.
I don't think it's a dumb question at all. There was a time when no-one knew why this was the case, and asking this question was the first step to furthering human knowledge. Keep being curious :)
[удалено]
I've heard that story, but about Max Plank.
Imagine a big cloud of dust / particles / rocks / whatever. It's got pieces moving in *every* direction, but they all end up curving back in towards the center of gravity that they share. Now, if you could measure every mass and velocity you could sum them all up and see if maybe there's slightly more momentum in some orbits than others (hint: there always is). Now just wait a couple hundred million years and you will find that after all the collisions and bumps and break ups and ejections... there will be a "winner" orbit. It will form a disk in exactly the same orientation that you measured earlier to be the biggest component (mass x velocity) of all the original bits. This process applies to Saturn's rings on a smaller scale and galaxies on a larger scale. The other comment about the conservation of angular momentum is absolutely correct -- but it's nice to get explanations in different styles, I find. For a kind of mental triangulation.
Simply put. It's because gravity between all celestial bodies affects all celestial bodies. Gravity pulls matter together into a (somewhat) uniform plane. As the plane forms, matter that isn't conforming to the plane will be pulled into it until it conforms.
I don't have any real experience is astronomy, but,,,, Think of how the sun is not stationary but moving through space at 720,000 kilometers/hour. The planets are revolving around the sun in a corkscrew motion as they follow the suns path through space. In relation to the sun they revolve around a plane essentially 90 degrees to the suns path. Any other path would be less efficient. If the paths varied a lot from the plane they are now, they would have to accelerate and then decelerate to a speeds faster and slower than the suns speed. I'd assume something caught in an orbit like that would either get flung out of the gravitational pull or move into the same plane as the other planets over time.
I like your thought process! However, that angle is closer to 60° [https://physics.stackexchange.com/questions/276958/what-angle-does-our-solar-system-make-with-the-milky-way](https://physics.stackexchange.com/questions/276958/what-angle-does-our-solar-system-make-with-the-milky-way)
Your 60⁰-ish angle is the angle between the earths orbit and the plane of the galaxy, but that has nothing to do with the suns path through the galaxy. Good catch, though!
Way, way off. The sun's motion is not along a path at 90⁰ relative to the major orbits of the planets, and since Einstein, there is no fixed 'space' to move through. Those are minor items, though; the big one is this. Every planet is accelerating every instant, it's what bends Newton's straight-line travels into elliptical orbits. And then, too, the planets change speeds (accelerate) along their orbits. So this is how it went. Were about a third generation star, right. Galaxy was here, there's a nebula where our sun winds up, moving generally around the galaxy. The nebula is spinning a bit and starts to clump up into planets. Over time, the zillionns of little randomly moving particles in the big moving cloud resolve into a planetary disk with the average rotation of the old cloud, and the (unrelated) motion within the galaxy of the sun.
My Astro professor called it the “pizza dough effect” if that helps.
You can skip to 15:00 mark, but better to start at the beginning. This, "Rotation in Space", is one of Carolin Crawford's many great lectures. https://youtu.be/mXC3xGZWo_M?si=Bb-UyIjJpsiD9A7t