In solar system we have all planets roughly on the same plane. Is it true for all of the star systems (or at least for those that we have observed so far) with multiple planets in our galaxy/other galaxies?

If not are there any other patterns e.g.?


Do planets on other star systems form ellipse orbits like in our solar system?

The solution of two bodies in the gravitational field of each other are conic sections.

This can be:

1) a straight line trajectory: falling on each other

2)a parabola , where one is at rest sitting in the focus of the parabola. It may still be a collision trajectory

3)A hyperbola, where one sits at rest on the hyperbolic focus and the other swings away to infinity, a scattering phenomenon

4) an ellipse, where one sits at resting on one of the foci and the other has the elliptical path. The circle is a limiting case of the elipse.

This is true for all regions of the universe.

Once more than two bodies are involved, the trajectories are affected by the gravitational fields of each other, and many body trajectories can be achieved only with numerical solutions and approximations. In reality nothing is really an ellipse in the any body solutions.

In solar system we have all planets roughly on the same plane.

This is an observational fact, used to model how the planetary system was formed for a nebulous rotating primordial matter cloud. This is discussed here.

Is it true for all of the star systems (or at least for those that we have observed so far) with multiple planets in our galaxy/other galaxies?

It will depend on how the system was formed. In general planets might be trapped by a star that did not generate them, and then they will have an orbit outside the plane.

  • $\begingroup$ Or they might have migrated and interacted gravitationally with other planets in the star system. Capturing a rogue planet is currently deemed to be rather unlikely. Much more likely is that a planet kicks another planet out as a rogue planet and takes on a rather odd orbit due to that interaction. $\endgroup$ – David Hammen Dec 25 '16 at 14:38

First off, there are only eight planets in the universe. Those things that look like planets, act like planets, were formed as planets, but don't happen to orbit the Sun -- They're exoplanets. This is an issue that the International Astronomical Union (IAU) must eventually address.

Astronomers have found a number of exoplanets that don't come anywhere close to what is seen in our own solar system. Some stellar systems appear to be just like ours, with the exoplanets having nearly circular orbits in a plane that is nearly parallel to the central star's rotation.

Other stellar systems? Not so much. Astronomers have found stellar systems with giant planets orbiting as close as Mercury, stellar systems with planets in highly non-circular orbits, and stellar systems with planets orbiting highly inclined with respect to the central star's rotation. The discovery of those stellar systems threw a wrench into the nice pretty picture of planetary formation that had been developed up until the 1990s.

This has also thrown a wrench into models of how our own solar system formed. The pretty picture developed over centuries up until the 1990s is pretty much out; there are too many problems with that pretty picture. What's the right explanation? The dust has not yet settled. This is a good thing. It gives young smart people a nice hard problem to attack in their young professional careers.

The day when science already has an answer for every question is the day science dies. Fortunately, that day is yet to come.

  • $\begingroup$ Thank you for a long answer, I just want to double check I understood it correctly: there are many systems where exoplanets are moving on the same plane like in the solar system, but there are other possibilities as well where they follow some other patterns (and those were discovered relatively recently, so they should be rather exceptional) ? $\endgroup$ – Ilya Chernomordik Dec 25 '16 at 8:13
  • $\begingroup$ @IlyaChernomordik -- All exoplanets were discovered recently. The first exoplanet was discovered in 1988. That's recent. The vast majority have been discovered in the last ten years, which is extremely recent. A few star systems have multiple planets all in nearly circular orbits, and orbiting in roughly the same orbital plane. Others have but one or two planets, some of them in highly eccentric or highly inclined orbits. $\endgroup$ – David Hammen Dec 25 '16 at 14:34

Not sure if you are looking for theory as well as the observational question you asked, but this may help. The process of star formation is believed to involve a gas and debris field converging under it's own gravity. Most planets are believed to form from the debris that converges to an accretion disk. It's a disk because there are so many collisions between particles that don't travel in the same direction. Like the rings around saturn. All these planets from the disk naturally end up in orbits in a plane. But some can be deflected by late collisions and some bodies may be captured late so could have any orbit.

  • $\begingroup$ The disc can form afterwards also. For example a spiral galaxy forming from a spherical galaxy. In addition to that the orbits will tend to go circular and on a flat plane if there are Enouph tidal forces involved. $\endgroup$ – Bill Alsept Dec 27 '16 at 6:51

The laws of gravity would be the same everywhere. Orbits are not always elliptical it's just hard to get and keep a perfectly circular one.

  • 1
    $\begingroup$ Its a question about the alignment of orbital planes not their eccentricity (how eliptical they are). $\endgroup$ – JMLCarter Dec 25 '16 at 2:53
  • $\begingroup$ @JMLCarter it's two separate questions. The main question is about elliptical orbits. The second part is about the planes. The first part of my answer is correct for either question so there's no reason to down vote. $\endgroup$ – Bill Alsept Dec 25 '16 at 17:40

protected by Qmechanic Dec 25 '16 at 9:34

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