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?

  • $\begingroup$ I may be in over my head here because I am just a layman, but I found this concept intriguing. Of course to respond in this way may break protocol, in which case I withdraw. If not, then what I find interesting in all this is that the Cambrian Explosion in evolution occurred at about the same time the solar system was captured by the Milky Way. I suspect a connection. Oliver $\endgroup$
    – user13191
    Jun 21, 2016 at 17:35
  • 3
    $\begingroup$ @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? $\endgroup$
    – called2voyage
    Jun 21, 2016 at 18:31
  • $\begingroup$ 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 $\endgroup$
    – Chris
    Apr 6, 2017 at 16:11
  • $\begingroup$ 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. $\endgroup$
    – Chris
    Apr 6, 2017 at 16:11
  • $\begingroup$ @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. $\endgroup$ Apr 6, 2017 at 22:52

2 Answers 2


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, 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)

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). 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, and some turbulence (subsonic or slightly supersonic, also in accordance to observations), and you will get a misalignement of the rotation axis, due to turbulence.

  • $\begingroup$ 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°? $\endgroup$ Nov 2, 2014 at 0:26
  • $\begingroup$ 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. $\endgroup$
    – MBR
    Nov 3, 2014 at 10:13
  • 6
    $\begingroup$ 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. $\endgroup$
    – ProfRob
    Apr 5, 2015 at 10:38
  • $\begingroup$ @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. $\endgroup$
    – Luaan
    Dec 4, 2019 at 7:34

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

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.

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.

  • 2
    $\begingroup$ 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. $\endgroup$
    – MBR
    Oct 9, 2013 at 8:44
  • $\begingroup$ This is a fair point - something I had not considered. $\endgroup$
    – astromax
    Oct 9, 2013 at 22:23
  • $\begingroup$ 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? $\endgroup$
    – astromax
    Oct 21, 2013 at 14:00
  • 3
    $\begingroup$ "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! $\endgroup$
    – MBR
    Oct 21, 2013 at 14:41

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .