Spherical vs. disk orbits?

It seems objects form disk orbits around more massive objects when they are close by the center of mass of that massive object, and then slowly as objects spread out further and further away, they start to form more random spherical orbits. You see examples of this everywhere, like in our solar system, where all of the inner planets, from Mercury to Neptune, are oriented in a tight plane around the ecliptic of the Sun, but as the objects get farther and farther away they start to orient themselves more randomly. Pluto shows more independence in its orientation than the inner planets, and further out they get even more random. Another example is the Milky Way, where inner stars form a disk, but the outer stars form a spherical halo.

Question is, is there a formula or law that has been formulated about when this is likely to happen? Something similar to a Hill Sphere, or a Roche Limit, but one that determines disk vs. spherical orientation.


I assume that it has something to do with tidal effects of gravity.

9 Answers

  • G
    Lv 4
    8 months ago


    Star creation starts with a supernova spewing 'celestial building blocks' from the poles of a rotating singularity, creating a disk of orbiting matter.

    As this matter coalesses it acts upon itself and chaotic motion takes hold. The further from its point of orbit the faster the effects set in.

    Then galaxies collide and it starts all over again.

  • D g
    Lv 7
    8 months ago

    think of an explosion from an object that  rotates like a sun does

    the  explosion will be out in all directions  but  you must remember more mass was in the equator of the object  that  was rotating before the  explosion 

    so  more mass will be at that location  then others  this slight increase in mass will mean the  center of mass will be along a disk along the equator of the  exploded object 

    the other  small objects will be pulled toward the  center   by gravity 

    over time that is   a large amount of time  

    there can be a  slight  difference in the    orbits because of colisions  changing   the momentum of the object   like when the  big   planet hit  earth when it was forming   it could have knocked earth off  on an angle   and   caused it to get a   orbit out of plane of the other planets 

  • 8 months ago

    Nebular theory... 

    Varying sizes of bits of material orbit a common center in a cloud; over time, some larger bits attract smaller bits through gravity, growing larger, attracting even more material.  As time advances, the larger chunks of material pull the lighter masses from other orbits into it's plane, and the cloud flattens out to a disk. Inside that disk, planets begin to form as the larger chunks collect the material from the disk, growing larger and larger. In the outer portions of the cloud, where the material is sparse, and the objects small, they may never become part of the disk forming nearer to the proto-star. 

  • cosmo
    Lv 7
    8 months ago

    Consider moons orbiting a planet.  If the planet is rotating, it will be somewhat oblate, bulging out in the equator.  Moon orbits in the plane of the equator will be stable, whereas moon orbits that are out of that plane will be continuously perturbed. 

    The angular momentum vector of most objects in the Solar System are just aligned with the angular momentum vector of the interstellar cloud that formed the Solar System, since most processes in the formation conserved angular momentum.

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  • 8 months ago

    All orbits must be in a plane. A planet can not move out of its elliptical path. The original orientation of an orbit depends on its initial velocity when it was formed. Because the cloud that formed the sun and planets was rotating, most planets orbit in the same plane.

  • Zardoz
    Lv 7
    8 months ago

    Because the disk collapses upon itself. Things above or below the mean plane of mass are pulled into the plane by gravity. When the density of the material within the plane is low enough its gravitational force is too low to pull the randomly orbiting material into it in a reasonable amount of time.

    Source(s): [n] = 10ⁿ
  • 8 months ago

    Actually, the orbits of the 8 major planets ate tilted at various angles to Earth's ecliptic plane. The Sun's equatorial plane is tilted at 7° to the ecliptic.

    The Milky Way's core is a spherical distribution of stars and globular of stars. With the arms of thm Illy Way galaxy further out. There is. O spherical halo of stars around the milky way Galaxy. Other GALAXIES in the Local Group have a spherical distribution around the Milky Way Galaxy. That does NOT include the Andromeda I (M31) Galaxy that has its own local group that are included in the Virgo 81 super cluster of galaxies.

    There are several reasons for this. One is the conservation of angular momentum. The other reason is insufficient nt *** to form a sphere. Other resomsare collusions as planets are forming around stars. We have three plats that have rotational axes that are severly tilted from the planes of their orbits because if 1 or more collisions, including glancing collisions, with planet or dwarf planet size. 

    I am not going to re type everything I put in sources. However, I am going to add that centrifugal force is a fictional force. Gravity is a centripetal force. Orbits are elliptical or sinusoidal be cause of the gravity and tidal affects of other bodies. 

    Conservation of momentum and insufficient mass to form a spherical distribution are the main reasons for discs. The solar systems orbit around Sagittarius A" is sinusoidal, not elliptical, are a a spiral, because the Mille Way Galaxy and Local Group are moving  too. 

    Are you dizzy yet? Take a break. Especially if you have a headache. 

    Source(s): bodies, Venus, Uranus and Pluto. Inertia is another reason. A force has to applied to change the direction an object is traveling., A collision is a force, so is gravity, So is pressure.. The inverse square of the distance law of gravity is another reason. all of those favors are going to create a disc around the center of mass, the barycenter, of multi body system.like a planetary system. We have found planetary systems where the orbits of t, nof in a disc or torus. The iverse square law of gravity is another reaso e planets are tilted at all a goes to each other,
  • 8 months ago

    The norm for satellites is orbiting in the ecliptic, like the equator of the parent planet.

    Yes, lots of math in this and the book on celestial dynamics is big.

  • 8 months ago

    The reason why planetary orbits tend to form a disk is that they accrete from material that was already revolving around the star in a diffuse disk.  And the reason for the formation of THAT protoplanetary disk is simply centrifugal force.  The star in its formative millennia was accumulating material, but as that glob was spinning, the equatorial parts of it spread out through simple centrifugal force.  And they spread out in the direction of the central plane of the rotation, not in some random direction -- because the centrifugal force is a vector in the plane of rotation, but directed away from the center.

    Many objects farther away were never part of the protoplanetary disk, but were captured later.  Or their greater distance from the star allowed their motions to be "perturbed" by random fly-bys.  Within the system of our inner planets plus gas giants, the planets may perturb one another's orbits, but on the whole tend to stabilize them into circular paths.  The stars whose planets have more circular orbits are the stars that have large numbers of planets. 

    Source(s): For the final point, see Limbach & Turner (2015) in Proc. Natl. Acad. Sci.
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