Pluto has a high orbital inclination compared to the planets in our solar system. What has caused Pluto to have such a different orbit -- was it always like this, or did something happen to make it so?

  • $\begingroup$ It's also fascinating that Orcus (en.wikipedia.org/wiki/90482_Orcus) is almost the same - 20 degrees and an almost identical orbit... I wonder if there's a common reason... $\endgroup$
    – Andy
    Jul 23, 2015 at 15:21
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    $\begingroup$ AFAIK, the basic models today say that Pluto formed in a circular orbit in a thin protoplanetary disk, like all planets. Pluto's orbit became eccentric and inclined because of gravitational interaction with migrating giant planets soon after their formation. $\endgroup$
    – LocalFluff
    Jul 23, 2015 at 20:25
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    $\begingroup$ It's actually typical for Kuiper belt objects to have high inclination. $\endgroup$
    – Mithoron
    Jul 23, 2015 at 22:40
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    $\begingroup$ A very interesting paper (I skimmed it last night but the maths will need more study!): staff.on.br/rodney/topicos/1/mal_plut_93.pdf As @LocalFluff says interacton with Neptune as it migrated outwards caused Pluto's resonance, then its enlargement to an elliptical orbit, and finally its orbital inclination. (Also probably explains why Orcus went a similar way.) $\endgroup$
    – Andy
    Jul 24, 2015 at 7:32
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    $\begingroup$ I'm not sure if this justifies an answer, but the Kozai mechanism has sometimes been invoked. $\endgroup$
    – HDE 226868
    Jul 26, 2015 at 15:06

1 Answer 1


I think the best answer is that there is no particular reason.

In any planetary system, most orbits tend to stay close to a common plane - close, but not exactly there. Even the big planets are slightly out-of-plane with each other, but the differences are tiny.

As you move away from the bulk of the planetary system's mass, smaller bodies tend to be more random. They are more easily deviated from encounters and near misses. Their origins might be different from the rest. If they get close to the outskirts of the system, that's a more unruly place, and orbit-changing events are more likely - especially for small bodies. Finally, the whole distribution of orbital planes has a bit of a stochastic (random) component anyway, and there will always be outliers that are quite different from the bulk.

In theory, even some larger planets could be significantly "out of plane" (much more than they are right now), but that's unlikely and it tends to be smoothed out over large periods of time.

So, Pluto is different because it's smaller and it's not really a planet, but don't attach too much significance to it.

Try to install Universe Sandbox and play with some of the included scenarios. Big systems bound by gravity can be pretty complex, and completely orderly configurations are rare.


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