<p>What you could think at first, regarding the orientation of any planetary system, is that it should be roughly in the plane of the galaxy, simply by angular momentum conservation.</p>

<p>But, when <a href="http://www.circumstellardisks.org/resolved.php?key=incl" rel="noreferrer">you take a look at observations</a>, you see that protoplanetary disks orientation is not what you would expect, with no preferential orientation (protoplanetary disks are embryo of planetary systems, that makes them interesting). In the following figure, the orientation corresponds to the inclination between the line of sight and the rotation axis of the disk.</p>

<p><img src="https://i.sstatic.net/7Zh8L.png" alt="disk orientation (own work, CC-by-nc-sa)"></p>

<p><strong>Why there is this distribution of orientation?</strong></p>

<p>The angular momentum scenario is nice but far to simple: star formation occurs in gas clouds in the interstellar medium, and <a href="http://adsabs.harvard.edu/abs/1981MNRAS.194..809L" rel="noreferrer">these clouds are known to be turbulent (Larson, 1981)</a>. Turbulence simply disrupts the gas, and is dominent over the global angular momentum of the cloud. Actually, you can even test that with numerical simulations of star formation: put an initial angular momentum <a href="http://adsabs.harvard.edu/abs/1993ApJ...406..528G" rel="noreferrer">consistent with observations</a>, and some turbulence (subsonic or slightly supersonic, <a href="http://adsabs.harvard.edu/abs/2007prpl.conf...33W" rel="noreferrer">also in accordance to observations</a>), and you will get <a href="http://adsabs.harvard.edu/abs/2013A%26A...554A..17J" rel="noreferrer">a misalignement of the rotation axis</a>, due to turbulence.</p>

CC BY-SA 3.0
2015-04-05T10:38:27.453Z
Your plot is a histogram of the inclination of the disk to the line of sight, so without further analysis it tells you nothing about the orientation wrt Galactic plane because these disks are around objects spread all over the sky.
ProfRob
CC BY-SA 4.0
2019-12-04T07:34:34.497Z
@pabouk Planetary tilt isn't static. It's thought that without the Moon, the Earth's tilt would be much more varied than it is. The same is true of the other planets. Even in modern times, there's Uranus (97 °) and Venus (177 °), and the values near 30 ° (Earth, Mars, Saturn, Neptune) aren't exactly small. There's probably also a bit of anthropic principle at play - having stable axial tilt (like Earth does thanks to the Moon) might be important for the development of complex and/or land life. Evolution can't deal with cycles where the surface becomes uninhabitable for millions of years.
Luaan
CC BY-SA 3.0
2014-11-02T00:26:03.140Z
Can this be extrapolated to a smaller scale? If yes then why most of the planets in the Solar system have axial tilt smaller than 30°?
pabouk - Ukraine stay strong
CC BY-SA 3.0
2014-11-03T10:13:37.730Z
You can have a look on the Kepler data, that shows the same kind of trend (lots of exoplanets with large axial tilt). So it seems that our Solar System is not very generic, but it isn't weird either from a statistic point of view. And actually, our situation is easier to understand from a physical point of view than all these tilted systems.
MBR
CC BY-SA 3.0
2013-10-09T08:43:25.563Z
2013-10-21T14:33:30.103Z
2013-10-21T14:33:30.103Z
MBR
<p>The tilt of our solar system (or any star system) is determined by the net angular momentum of the gas cloud from which it formed. This might be a bit of a vague answer, but over time, the formation of stars and their respective planets is thought to look something like this:</p>

<p><img src="https://i.sstatic.net/fMKYx.jpg" alt="Formation of a star"></p>

<p>Other influences (net forces: maybe nearby massive objects, or other components of the galaxy) on the tilt of the plane of a stellar system could certainly cause a precession of its axis with time. As an example of this see the precession of a <a href="http://en.wikipedia.org/wiki/Gyroscope" rel="noreferrer">gyroscope</a>.</p>

<p>It would be really interesting to know the distribution of angles between the plane of the galaxy and the plane of stellar systems, though I'd bet that many of them are simply aligned with the disk itself.</p>

CC BY-SA 3.0
2013-10-09T08:44:02.753Z
I don't agree, precession will be clearly negligible compared to the initial effect of turbulence during the first stage of the star formation process.
MBR
CC BY-SA 3.0
2013-10-09T22:23:09.490Z
This is a fair point - something I had not considered.
astromax
CC BY-SA 3.0
2013-10-21T14:00:02.150Z
Also, when you say turbulence, can you elaborate? Your turbulence would have to produce a change in the velocity field perpendicular to the plane of the disk. What turbulent mechanisms are you referring to here?
astromax
CC BY-SA 3.0
2013-10-21T14:41:25.737Z
"Turbulence" refers to turbulent motions in the ISM. If you want to know about the properties of turbulence, it is probably a mixture of compressible and solenoidal modes. If you want to know about the sources of turbulence in the ISM, they are numerous (bipolar outflows, HII regions, SN explosions, differential rotation of the galaxy etc.). If you wonder about turbulence in the ISM, feel free to ask a question so I could elaborate more!
MBR
CC BY-SA 3.0
2013-10-09T01:31:30.640Z
2013-10-09T01:31:30.640Z
astromax
<p>Our own solar system is "tipped" by about 63 degrees with respect to the plane of the galaxy. Has it ever been researched or is there any scientific theory which could explain the reason why our solar system and solar systems in general are not "in-line" to the galaxy's plane? What exactly determines the orientation of solar systems?</p>

CC BY-SA 3.0
2016-06-21T18:31:42.933Z
@oliver "captured by the Milky Way"? I see no answer other than your own that suggests this, and yours does not provide a proposed date of capture. How then does the Cambrian Explosion coincide with it?
called2voyage
CC BY-SA 3.0
2017-04-06T16:11:43.600Z
I do not have much experience in astronomy whatsoever but I would like to postulate a theory anyway. Our solar system has roughly a 63° tilt in respects to the Milky Way's rotational axis correct? We observe that our system is not alone in the tilt is what I think I understand from reading above. What is the angular tilt of Andromeda Galaxy in relation to the Milky Way Galaxy? Is it possible that Andromeda passed within close proximity to our galaxy some 4-5 billion years ago along the edge that our sun was currently in, with gravitational force extracting large pieces of matter from our sun w
Chris
CC BY-SA 3.0
2017-04-06T16:11:43.600Z
hich later congealed to form the planetary system we live in today? Also not only forming our system with a tilt but also causing the formation of other planetary systems with a varying tilt in relation to its distance from Andromeda and the gravitaional force exerted as Andromeda passed by? Like I said before, I have no astronomical experience and so this theory is not claimed to be nothing more than a simple suggestion.
Chris
CC BY-SA 3.0
2017-04-06T22:52:43.937Z
@e-sushi Star systems are formed from bubbles of stuff that are swirling every which way, like eddies do in a mountain creek even though the creek as a whole moves downhill. Download and install Universe Sandbox and play some simulations, especially the galactic collisions and other collision scenarios - it will show you how on a small, local scale things may end up spinning in all kinds of directions even when the whole galaxy has an overall direction and spin.
Florin Andrei
CC BY-SA 3.0
2017-04-06T23:23:29.903Z
@Chris Any reason you didn't post your extended comment as an answer? Don't get me wrong, but I (and most other users) prefer voting on answers instead of comments. You might even gain some reputation when doing so.
e-sushi
CC BY-SA 3.0
2017-04-06T23:23:51.197Z
@FlorinAndrei Same to you — Any reason you didn't post your extended comment as an answer? Don't get me wrong, but I (and most other users) prefer voting on answers instead of comments. You might even gain some reputation when doing so.
e-sushi
CC BY-SA 4.0
2019-10-29T21:17:56.123Z
The angle is actually 60 degrees. The number 63 is the angle between the Galactic plane and celestial equator.
ProfRob
<galaxy><solar-system><inclination>
Why is our solar system "tipped" about 63° with respect to the plane of our galaxy?
e-sushi
# Why is our solar system "tipped" about 63° with respect to the plane of our galaxy?

(Asked by: username_0 on 2013-10-09)

Our own solar system is "tipped" by about 63 degrees with respect to the plane of the galaxy. Has it ever been researched or is there any scientific theory which could explain the reason why our solar system and solar systems in general are not "in-line" to the galaxy's plane? What exactly determines the orientation of solar systems?

**Tags:** galaxy, solar-system, inclination
> **Comments:**
> **username_1**: @oliver "captured by the Milky Way"? I see no answer other than your own that suggests this, and yours does not provide a proposed date of capture. How then does the Cambrian Explosion coincide with it?  
> **username_2**: I do not have much experience in astronomy whatsoever but I would like to postulate a theory anyway. Our solar system has roughly a 63° tilt in respects to the Milky Way's rotational axis correct? We observe that our system is not alone in the tilt is what I think I understand from reading above. What is the angular tilt of Andromeda Galaxy in relation to the Milky Way Galaxy? Is it possible that Andromeda passed within close proximity to our galaxy some 4-5 billion years ago along the edge that our sun was currently in, with gravitational force extracting large pieces of matter from our sun w  
> **username_2**: hich later congealed to form the planetary system we live in today? Also not only forming our system with a tilt but also causing the formation of other planetary systems with a varying tilt in relation to its distance from Andromeda and the gravitaional force exerted as Andromeda passed by? Like I said before, I have no astronomical experience and so this theory is not claimed to be nothing more than a simple suggestion.  
> **username_3**: @e-sushi Star systems are formed from bubbles of stuff that are swirling every which way, like eddies do in a mountain creek even though the creek as a whole moves downhill. Download and install Universe Sandbox and play some simulations, especially the galactic collisions and other collision scenarios - it will show you how on a small, local scale things may end up spinning in all kinds of directions even when the whole galaxy has an overall direction and spin.  
> **username_0**: @Chris Any reason you didn't post your extended comment as an answer? Don't get me wrong, but I (and most other users) prefer voting on answers instead of comments. You might even gain some reputation when doing so.  
> **username_0**: @FlorinAndrei Same to you — Any reason you didn't post your extended comment as an answer? Don't get me wrong, but I (and most other users) prefer voting on answers instead of comments. You might even gain some reputation when doing so.  
> **username_4**: The angle is actually 60 degrees. The number 63 is the angle between the Galactic plane and celestial equator.  

---

## 2 answers

### Answer by username_8 on 2013-10-09. Score: 19 | Accepted answer

The tilt of our solar system (or any star system) is determined by the net angular momentum of the gas cloud from which it formed. This might be a bit of a vague answer, but over time, the formation of stars and their respective planets is thought to look something like this:

![Formation of a star](https://i.sstatic.net/fMKYx.jpg)

Other influences (net forces: maybe nearby massive objects, or other components of the galaxy) on the tilt of the plane of a stellar system could certainly cause a precession of its axis with time. As an example of this see the precession of a [gyroscope](http://en.wikipedia.org/wiki/Gyroscope).

It would be really interesting to know the distribution of angles between the plane of the galaxy and the plane of stellar systems, though I'd bet that many of them are simply aligned with the disk itself.

> **Comments:**
> **username_5**: I don't agree, precession will be clearly negligible compared to the initial effect of turbulence during the first stage of the star formation process.  
> **username_8**: This is a fair point - something I had not considered.  
> **username_8**: Also, when you say turbulence, can you elaborate? Your turbulence would have to produce a change in the velocity field perpendicular to the plane of the disk. What turbulent mechanisms are you referring to here?  
> **username_5**: "Turbulence" refers to turbulent motions in the ISM. If you want to know about the properties of turbulence, it is probably a mixture of compressible and solenoidal modes. If you want to know about the sources of turbulence in the ISM, they are numerous (bipolar outflows, HII regions, SN explosions, differential rotation of the galaxy etc.). If you wonder about turbulence in the ISM, feel free to ask a question so I could elaborate more!  

---

### Answer by username_5 on 2013-10-09. Score: 24

What you could think at first, regarding the orientation of any planetary system, is that it should be roughly in the plane of the galaxy, simply by angular momentum conservation.

But, when [you take a look at observations](http://www.circumstellardisks.org/resolved.php?key=incl), you see that protoplanetary disks orientation is not what you would expect, with no preferential orientation (protoplanetary disks are embryo of planetary systems, that makes them interesting). In the following figure, the orientation corresponds to the inclination between the line of sight and the rotation axis of the disk.

![disk orientation (own work, CC-by-nc-sa)](https://i.sstatic.net/7Zh8L.png)

**Why there is this distribution of orientation?**

The angular momentum scenario is nice but far to simple: star formation occurs in gas clouds in the interstellar medium, and [these clouds are known to be turbulent (Larson, 1981)](http://adsabs.harvard.edu/abs/1981MNRAS.194..809L). Turbulence simply disrupts the gas, and is dominent over the global angular momentum of the cloud. Actually, you can even test that with numerical simulations of star formation: put an initial angular momentum [consistent with observations](http://adsabs.harvard.edu/abs/1993ApJ...406..528G), and some turbulence (subsonic or slightly supersonic, [also in accordance to observations](http://adsabs.harvard.edu/abs/2007prpl.conf...33W)), and you will get [a misalignement of the rotation axis](http://adsabs.harvard.edu/abs/2013A%26A...554A..17J), due to turbulence.

> **Comments:**
> **username_7**: Can this be extrapolated to a smaller scale? If yes then why most of the planets in the Solar system have axial tilt smaller than 30°?  
> **username_5**: You can have a look on the Kepler data, that shows the same kind of trend (lots of exoplanets with large axial tilt). So it seems that our Solar System is not very generic, but it isn't weird either from a statistic point of view. And actually, our situation is easier to understand from a physical point of view than all these tilted systems.  
> **username_4**: Your plot is a histogram of the inclination of the disk to the line of sight, so without further analysis it tells you nothing about the orientation wrt Galactic plane because these disks are around objects spread all over the sky.  
> **username_6**: @pabouk Planetary tilt isn't static. It's thought that without the Moon, the Earth's tilt would be much more varied than it is. The same is true of the other planets. Even in modern times, there's Uranus (97 °) and Venus (177 °), and the values near 30 ° (Earth, Mars, Saturn, Neptune) aren't exactly small. There's probably also a bit of anthropic principle at play - having stable axial tilt (like Earth does thanks to the Moon) might be important for the development of complex and/or land life. Evolution can't deal with cycles where the surface becomes uninhabitable for millions of years.  

---

