# Planets Orbit / Plane around the Sun? **URL:** \ **Category:** Factual Questions\ **Created:** [March 7, 2004, 10:10pm UTC](https://boards.straightdope.com/t/planets-orbit-plane-around-the-sun/233023 "2004-03-07T22:10:44Z")\ **Posts on this page:** 16\ **Page:** 1
**Author:** ![DrDoom](https://avatars.discourse-cdn.com/v4/letter/d/e19b73/32.png) [@DrDoom](https://boards.straightdope.com/u/DrDoom)\ **Post date:** [March 7, 2004, 10:10pm UTC](https://boards.straightdope.com/t/planets-orbit-plane-around-the-sun/233023/1 "2004-03-07T22:10:44Z")
What effect caused the planets in our solar system to orbit in the same direction and, essentially, in the same plane around the sun? Would all other solar systems follow this model as well? ---
**Author:** ![Mangetout](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mangetout/32/19_2.png) [@Mangetout](https://boards.straightdope.com/u/Mangetout)\ **Post date:** [March 7, 2004, 10:25pm UTC](https://boards.straightdope.com/t/planets-orbit-plane-around-the-sun/233023/2 "2004-03-07T22:25:44Z")
I believe it is because the solar system (including the sun) was originally formed from a disc of gas and dust that was orbiting around its own dense centre. It is quite likely that other solar systems would do the same. The reason why it was a disc though, is slightly involved, but in simple terms, it is just the most stable configuration of a bunch of moving, co-orbiting matter. ---
**Author:** ![R-Con](https://avatars.discourse-cdn.com/v4/letter/r/858c86/32.png) [@R-Con](https://boards.straightdope.com/u/R-Con)\ **Post date:** [March 7, 2004, 10:34pm UTC](https://boards.straightdope.com/t/planets-orbit-plane-around-the-sun/233023/3 "2004-03-07T22:34:52Z")
> [@DrDoom](#): > > What effect caused the planets in our solar system to orbit in the same direction and, essentially, in the same plane around the sun? Would all other solar systems follow this model as well? From [Mad Science:](http://www.madsci.org/posts/archives/oct98/904773784.As.r.html) > [@](#): > > Well, in general, the orbits of the planets are all in the same plane (in technical terms, they are "coplanar’’)! The differences are actually pretty small; the largest is Pluto which has about a 17% tilt with respect to the Earth’s. We usually use the Earth’s orbit as the reference. We might as well, we live here! > > The reason the orbits are roughly coplanar is due to the way the solar system formed. We started out as a gas cloud in space, and it was probably roughly spherical (though it need not have been). Something made the cloud start to collapse. Perhaps it was a shock wave from a nearby supernova, or it collided with another cloud. Whatever it was, when the cloud started to collapse, any tiny bit of circular motion it had inside would get hugely amplified, causing the cloud to rotate. [Think of an spinning ice skater—as she pulls her arms closer to her body or becomes smaller, she spins faster.] Something that rotates wants to flatten out, and so after a time the cloud became more disklike. So when the planets formed, they were all in about the same plane: the plane of the disk. > > Incidentally, we have detected disks of gas around other stars, like Beta Pictoris. There is even evidence that planets are forming there too! There is some debate as to whether Pluto should actually be called a planet - its orbit is so different to all the other planets (in both deviance from the mean plane and because it actually crosses Neptune’s orbit), and has characteristics shared by many objects in the Kuiper Belt (a bisk disk of icy stuff that more or less orbits around the sun, way, waaaay out…about 50 to 100 AU.) ---
**Author:** ![Liberal](https://avatars.discourse-cdn.com/v4/letter/l/848f3c/32.png) [@Liberal](https://boards.straightdope.com/u/Liberal)\ **Post date:** [March 7, 2004, 10:39pm UTC](https://boards.straightdope.com/t/planets-orbit-plane-around-the-sun/233023/4 "2004-03-07T22:39:20Z")
The phenomenon of the material gathering coplanarly is called accretion. See [this](http://imagine.gsfc.nasa.gov/docs/ask_astro/answers/001106a.html). ---
**Author:** ![MC\_Master\_of\_Ceremonies](https://avatars.discourse-cdn.com/v4/letter/m/bb73d2/32.png) [@MC\_Master\_of\_Ceremonies](https://boards.straightdope.com/u/MC_Master_of_Ceremonies)\ **Post date:** [March 7, 2004, 10:50pm UTC](https://boards.straightdope.com/t/planets-orbit-plane-around-the-sun/233023/5 "2004-03-07T22:50:29Z")
> [@Libertarian](#): > > The phenomenon of the material gathering coplanarly is called accretion. See [this](http://imagine.gsfc.nasa.gov/docs/ask_astro/answers/001106a.html). No it isn’t; as your link attests to, accretion (in astrophysics) is simply a when a body draws matter onto itself. ---
**Author:** ![Squink](https://avatars.discourse-cdn.com/v4/letter/s/b5e925/32.png) [@Squink](https://boards.straightdope.com/u/Squink)\ **Post date:** [March 8, 2004, 12:00am UTC](https://boards.straightdope.com/t/planets-orbit-plane-around-the-sun/233023/6 "2004-03-08T00:00:48Z")
> [@](#): > > Would all other solar systems follow this model as well? Pretty much. There’s a symmetry factor that comes into play here. If you have two bodies in orbit about a star in the same orbital plane, the gravitational interaction between those two bodies as they pass each other in their orbits will exert a force on each body that is nonzero only along the tsurface of the plane. In other words, gravitational interactions can move the bodies in and out in their orbits, but not up and down away from the plane. On the other hand, if two orbiting bodies do **not** fall in the same plane about the central star, every time they pass each other, they’ll be pulled out of their respective orbital planes and into new planes by the off-plane gravitational attraction. There could easily be examples of nonplanar solar systems that appear stable for an (astronomically) short time, a million or a billion years, but in the long run, the only gravitationally stable system is one in which all the planets lie along the same plane. ---
**Author:** ![Polycarp](https://avatars.discourse-cdn.com/v4/letter/p/82dd89/32.png) [@Polycarp](https://boards.straightdope.com/u/Polycarp)\ **Post date:** [March 8, 2004, 2:39am UTC](https://boards.straightdope.com/t/planets-orbit-plane-around-the-sun/233023/7 "2004-03-08T02:39:47Z")
> [@MC Master of Ceremonies](#): > > No it isn’t; as your link attests to, accretion (in astrophysics) is simply a when a body draws matter onto itself. True. However, a rotating body will generally form the material it accretes, prior to the accreting material’s impact with the body itself, into a disk coplanar with its equator. So while you’re technically correct, since most heavenly bodies do in fact rotate, **Lib** ’s allegation is accurate for purposes of discussion of normal bodies. ---
**Author:** ![Starguard](https://avatars.discourse-cdn.com/v4/letter/s/8dc957/32.png) [@Starguard](https://boards.straightdope.com/u/Starguard)\ **Post date:** [March 8, 2004, 1:31pm UTC](https://boards.straightdope.com/t/planets-orbit-plane-around-the-sun/233023/8 "2004-03-08T13:31:35Z")
Pluto orbits at an oblong plane that is tilted 17 degrees and is swings in toward the sun to the point that it actually crosses Neptunes orbit. How come this planetoid has an orbit of its own far different from all the other planets, and what is it about its orbit that stops it from actually hitting neptune or getting caught in neptunes gravitational field and becoming a satellite or “Moon” ---
**Author:** ![Mangetout](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mangetout/32/19_2.png) [@Mangetout](https://boards.straightdope.com/u/Mangetout)\ **Post date:** [March 8, 2004, 1:50pm UTC](https://boards.straightdope.com/t/planets-orbit-plane-around-the-sun/233023/9 "2004-03-08T13:50:58Z")
> [@Starguard](#): > > Pluto orbits at an oblong plane that is tilted 17 degrees and is swings in toward the sun to the point that it actually crosses Neptunes orbit. How come this planetoid has an orbit of its own far different from all the other planets, and what is it about its orbit that stops it from actually hitting neptune or getting caught in neptunes gravitational field and becoming a satellite or “Moon” I would imagine that the different orbital plane is the result of an impact at some point in Pluto’s past. As to why they don’t collide, I suspect luck is the answer, but we’re talking about enormous stretches of space and time: Pluto takes 248 years to complete a single orbit of the sun - Neptune takes 165 years - I’m not even sure if the orbital path of Pluto directly intersects that of Neptune (it doesn’t _have_ to in three-dimensional space, as Pluto’s orbit is out of the plane), but even if it did, the chances of both planets being at the point of intersection at the same time must be vanishingly small. ---
**Author:** ![sturmhauke](https://avatars.discourse-cdn.com/v4/letter/s/e47c2d/32.png) [@sturmhauke](https://boards.straightdope.com/u/sturmhauke)\ **Post date:** [March 8, 2004, 2:00pm UTC](https://boards.straightdope.com/t/planets-orbit-plane-around-the-sun/233023/10 "2004-03-08T14:00:37Z")
> [@Mangetout](#): > > Pluto takes 248 years to complete a single orbit of the sun - Neptune takes 165 years - I’m not even sure if the orbital path of Pluto directly intersects that of Neptune (it doesn’t _have_ to in three-dimensional space, as Pluto’s orbit is out of the plane), but even if it did, the chances of both planets being at the point of intersection at the same time must be vanishingly small. Look closer at those numbers. Pluto completes 2 orbits for every 3 of Neptune’s; they are locked into a (cue music) **Cosmic Dance of Eternity.** (bom-bam-bom-bam-ksshhh). Barring some outside interaction or the eventual death of the Sun, Pluto may never collide with Neptune. ---
**Author:** ![Squink](https://avatars.discourse-cdn.com/v4/letter/s/b5e925/32.png) [@Squink](https://boards.straightdope.com/u/Squink)\ **Post date:** [March 8, 2004, 2:18pm UTC](https://boards.straightdope.com/t/planets-orbit-plane-around-the-sun/233023/11 "2004-03-08T14:18:22Z")
> [@sturmhauke](#): > > they are locked into a (cue music) **Cosmic Dance of Eternity.** (bom-bam-bom-bam-ksshhh). Barring some outside interaction… Behold [Planet X](http://www.badastronomy.com/phpBB/viewtopic.php?t=11818)😉 ---
**Author:** ![Liberal](https://avatars.discourse-cdn.com/v4/letter/l/848f3c/32.png) [@Liberal](https://boards.straightdope.com/u/Liberal)\ **Post date:** [March 8, 2004, 4:03pm UTC](https://boards.straightdope.com/t/planets-orbit-plane-around-the-sun/233023/12 "2004-03-08T16:03:17Z")
> [@Polycarp](#): > > True. However, a rotating body will generally form the material it accretes, prior to the accreting material’s impact with the body itself, into a disk coplanar with its equator. > > So while you’re technically correct, since most heavenly bodies do in fact rotate, **Lib** ’s allegation is accurate for purposes of discussion of normal bodies. The only reason I knew it is because the question was previously answered here in General Questions, I believe by Chronos. It was when I inquired about why the matter around black holes surrounds them like rings of Saturn rather than three dimensionally like an atmosphere. I was referred to articles on accretion disks. ---
**Author:** ![RM\_Mentock](https://avatars.discourse-cdn.com/v4/letter/r/e274bd/32.png) [@RM\_Mentock](https://boards.straightdope.com/u/RM_Mentock)\ **Post date:** [March 8, 2004, 5:39pm UTC](https://boards.straightdope.com/t/planets-orbit-plane-around-the-sun/233023/13 "2004-03-08T17:39:31Z")
> [@Libertarian](#): > > The only reason I knew it is because the question was previously answered here in General Questions, I believe by Chronos. It was when I inquired about why the matter around black holes surrounds them like rings of Saturn rather than three dimensionally like an atmosphere. I was referred to articles on accretion disks. **MC Master of Ceremonies** objection, I think, was to the use of “accretion” instead of “accretion disk.” **Polycarp** said **MC Master of Ceremonies** was technically correct, which I usually read as “correct.” ---
**Author:** ![MC\_Master\_of\_Ceremonies](https://avatars.discourse-cdn.com/v4/letter/m/bb73d2/32.png) [@MC\_Master\_of\_Ceremonies](https://boards.straightdope.com/u/MC_Master_of_Ceremonies)\ **Post date:** [March 8, 2004, 5:41pm UTC](https://boards.straightdope.com/t/planets-orbit-plane-around-the-sun/233023/14 "2004-03-08T17:41:16Z")
> [@Polycarp](#): > > True. However, a rotating body will generally form the material it accretes, prior to the accreting material’s impact with the body itself, into a disk coplanar with its equator. > > So while you’re technically correct, since most heavenly bodies do in fact rotate, **Lib** ’s allegation is accurate for purposes of discussion of normal bodies. Not really, though the formation of the solar system certainly involved accretion the fact that the planets are approximately co-planar has very little to do with accretion. Accretion certainly does not necessarily mean the formation of a flat disk. ---
**Author:** ![Liberal](https://avatars.discourse-cdn.com/v4/letter/l/848f3c/32.png) [@Liberal](https://boards.straightdope.com/u/Liberal)\ **Post date:** [March 8, 2004, 8:54pm UTC](https://boards.straightdope.com/t/planets-orbit-plane-around-the-sun/233023/15 "2004-03-08T20:54:10Z")
Then I renew my question from yesteryear. Why is the material being sucked into black holes arranged coplanarly such that we see a dark disk inside whiteness? Were the material arranged all around the sphere like a cloud, we would not see the black hole. ---
**Author:** ![RM\_Mentock](https://avatars.discourse-cdn.com/v4/letter/r/e274bd/32.png) [@RM\_Mentock](https://boards.straightdope.com/u/RM_Mentock)\ **Post date:** [March 8, 2004, 10:40pm UTC](https://boards.straightdope.com/t/planets-orbit-plane-around-the-sun/233023/16 "2004-03-08T22:40:39Z")
> [@Libertarian](#): > > Then I renew my question from yesteryear. Why is the material being sucked into black holes arranged coplanarly such that we see a dark disk inside whiteness? Were the material arranged all around the sphere like a cloud, we would not see the black hole. You’ve shown great patience. [Your previous link](http://imagine.gsfc.nasa.gov/docs/ask_astro/answers/001106a.html) discussed accretion disks formed between two celestial bodies–one was being torn apart and drawn into the other. Of course two bodies orbit each other in a plane, so that’s almost a given. Tidal forces tear apart the smaller body and stretch it across the plane of the orbit.