Is it possible Planet Nine is shepherding the Kuiper Belt similar to the way Jupiter shepherds the asteroid belt?

I understand that very little is actually known about Planet Nine at this point, but has it been postulated that it has control over the Kuiper Belt? I don't exactly intend to read any theoretical papers on the existence of Planet Nine because I am sure it will be way over my head, but I understand that it is from the position of several Trans-Neptunian objects that its existence has any merit at all. So, I am wondering if part of that theory includes the Kuiper belt as a whole?

  • $\begingroup$ I've seen it referred to as "perturbing the orbits of the outer planets" $\endgroup$ Commented Feb 5, 2016 at 23:48
  • 2
    $\begingroup$ Similar question here astronomy.stackexchange.com/questions/13339/… Planet 9 was theorized based on scattered disk objects that are currently in the kuiper belt, not on observations of the kuiper belt. A picture might help. i.sstatic.net/BzWva.jpg Planet 9 can effect orbits in the scattered disk, but not the kuiper belt much, it's much too far away and it's thought to be lighter than Neptune. $\endgroup$
    – userLTK
    Commented Feb 6, 2016 at 4:23
  • $\begingroup$ Related: astronomy.stackexchange.com/questions/44809/… $\endgroup$
    – John
    Commented Jul 12, 2021 at 6:15

1 Answer 1


Estimates of Planet 9's orbit currently suggest that it doesn't have any major effect on the Kuiper Belt, because its orbit is too far away and on a different plane than the Kuiper belt, and from the inner Oort cloud, at 200 and 1200 aphelion and perihelion, However it does have an effect on Trans-Neptunian objects that transit through the Kuiper belt. It doesn't get closer than 4 times the distance of Pluto and it transits at a different plane to the Kuiper belt.

Shepherding is the act of actually creating and directing the asteroid belt by providing many objects with a semi stable orbit with too violent collisions to make a planet (biggest is Ceres at ${\rm 500 km}$ diameter), and having a massive effect on the unstable collection of asteroids, like making large stable groups around Jupiter's Lagrangian points at 60 degrees to Jupiter, and making fast resonant orbits that are not round like stable asteroids but periodically go close to Jupiter and then go straight through the inner asteroid belt and back to towards Jupiter actually in a triangle.


Neptune's orbit averages 30AU, and the Kuiper belt is generally held to be between Neptune and Pluto's orbits, Pluto orbits at 31-48AU.

In that sense, Pluto and Neptune are the two objects which have the biggest effect on the Kuiper belt.

The Trans-Neptunian objects all traverse the Kuiper belt, with their Perihelions ranging from 17 to 50 AU, and if Trans-Neptunian objects swing out towards Planet 9, it's a less stable orbit for them, than if they swing out away from planet 9, so all the large Kuiper belt objects swing away from the alledged direction of planet 9, where they can have a stable course without a transiting planet to interfere with them. Trans Neptunians tend to not align themselves with Planet 9's orbit and tend to find a balance away from Planet 9 and away from Jupiter and the majority of them don't get closer than Neptune, about 7/8ths of them are further than Neptune. https://en.wikipedia.org/wiki/List_of_trans-Neptunian_objects

The Trans-Neptunian objects are often referred to as Kuiper belt objects, and they didn't start their course to 100ds of AU's distance because of Planet 9, but now they are affected by planet 9 because they are in its vicinity over millions of years. In a million years, they have about 500 chances to approach planet 9, and 500,000 chances in a billion years.

The shepherding effect is complex, Jupiter accelerates objects very fast in stable orbits that resonate with it, it prevents planets from forming from the asteroid belt, and it disrupts the otherwise stable asteroid belt, sending objects fast through the asteroid belt and wherever, towards and away from the Sun. Jupiter created and maintains the asteroid belt which is unstable space debris, and it protects Earth from comets that want orbits that through its path.

Planet 9's inclination is about 30 degrees, so it can't interact with the inner Oort cloud, and the outer Oort cloud is too far away.


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