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Other than Pluto's moons (including Charon), which known body comes closest to Pluto, and how close? Neptune doesn't come closer than 16 au. What about Orcus, whose orbit is similar to Pluto's, or another dwarf planet?

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    $\begingroup$ Technically, many, many small Kuiper belt objects enter Pluto's Hill Sphere (or sphere of influence SOI) every day. So those would be the ones closest, but I think you are talking about large, major objects. $\endgroup$
    – WarpPrime
    Jan 19, 2021 at 14:01
  • $\begingroup$ @fasterthanlight I'm asking "which known body". This may include asteroids like Arrokoth. $\endgroup$ Jan 19, 2021 at 14:27
  • $\begingroup$ @fasterthanlight fascinating! So I've just asked How many solar system objects that can really qualify as a KBO are likely to enter Pluto's Hill sphere each day? $\endgroup$
    – uhoh
    Jan 19, 2021 at 14:39
  • $\begingroup$ You might want to look at plutinos $\endgroup$ Jan 20, 2021 at 4:04
  • $\begingroup$ @NilayGhosh Wikipedia is quite silent on the Pluto MOID of Plutinos. I'd like to know how close to Pluto they can come, which one closest. $\endgroup$ Jan 20, 2021 at 6:29

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Among neighborhood-clearing planets, it is not Neptune but Uranus that comes closest to Pluto. Uranus comes within a minimum of about 11 AU from Pluto. While the ellipses that make up the orbits of Pluto and Neptune come closer than that, the resonant relationship between Pluto and Neptune prevents both objects from occupying the closest approach points at the same time.

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Quaoar's orbit should bring it within about 670,000,000km (~4.48 AU) of Pluto in ~150 years, according to the scale model in Universe Sandbox.

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    $\begingroup$ According to Horizons, the next close approach occurs on 2148-Feb-19 (around 17:00 UTC), at a distance of 853643843 km ~= 5.7 AU. $\endgroup$
    – PM 2Ring
    May 8, 2023 at 14:34
  • $\begingroup$ Here's a Horizons query covering that timespan: ssd.jpl.nasa.gov/api/… $\endgroup$
    – PM 2Ring
    May 9, 2023 at 20:15

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