<p>Since (1) the mass of the Pluto/Charon system is very small compared with Neptune, and (2) their orbits are in 2:3 resonance, so the perturbation of Neptune's orbit would have been undetectable. University of Rochester has a good <a href="http://www.pas.rochester.edu/~blackman/ast104/perturbations.html" rel="nofollow noreferrer">explanation</a> of this. </p>

<blockquote>
  <p>The Accidental Discovery of Pluto</p>
  
  <p>Later supposed perturbations of the orbits of Uranus and Neptune suggested
  the presence of yet another planet beyond the orbit of Neptune.
  Eventually, in 1930, a new planet Pluto was discovered, but we now
  know that the calculations in this case were also in error because of
  an incorrect assumption about the mass of the new planet. It is now
  believed that the supposed deviations in the orbits of Neptune and
  Uranus were errors in measurement because the actual properties of
  Pluto would not have accounted for the supposed perturbations. Thus,
  the discovery of Pluto was a kind of accident</p>
</blockquote>

CC BY-SA 3.0
2018-02-23T12:38:08.237Z
I added the quote in case the link dies.
userLTK
CC BY-SA 4.0
2019-09-21T19:05:53.937Z
Because they are in resonance, some perturbation surely exists, but it affects their orbit significantly only on a much longer time. Probably the orbit of the Pluto is not an exact ellipse.
peterh
CC BY-SA 3.0
2018-02-23T04:45:09.003Z
2018-02-23T12:37:45.083Z
2018-02-23T12:37:45.083Z
Professor O
<p>Reading another question, I came across the argument that inconsistencies in Neptune's and Uranus' orbits lead to the discovery of Pluto.  <a href="http://pluto.jhuapl.edu/Participate/learn/What-We-Know.php?link=Discovery-of-Pluto" rel="nofollow noreferrer">This brief write-up</a> mentions Percival Lowell and William H. Pickering by name as two people who looked for the theoretical 9th planet.</p>

<p>My question is, were inconsistencies in Neptune's and Uranus' orbits detectable by early 20th century methods or were these scientists just chasing calculation or estimation errors with dreams of finding the next planet.  My (guess) is that Pluto is much too small, and too far away and just one of many similar mass kuiperbelt objects, so it's unlikely that it was really discovered by measured inconsistency in Uranus/Neptune orbits method, (despite the fact that <a href="http://coolcosmos.ipac.caltech.edu/ask/154-Who-discovered-Pluto-" rel="nofollow noreferrer">there are articles that say that's precisely how Pluto was discovered</a>).</p>

<p>In a nutshell, that's the question.  Was the wobble that Pluto's causes on Neptune's orbit observable by 1910-1930 observation methods.  And related, was the wobble that the entire kuiperbelt (some 20 to 50 times the mass of little pluto, but much more spread out), was that wobble detectible by 1910-1930 methods.</p>

<p>Hard math isn't necessary to me for an answer, as I find the math hard to follow sometimes, so feel free to answer with or without mathematical calculations.  </p>

CC BY-SA 3.0
2018-02-19T11:59:12.077Z
@Kozaky Good suggestion.   I found this, which says the predictions used for where to look for Pluto were basically bogus.   (LOL). 
 http://ircamera.as.arizona.edu/NatSci102/NatSci102/lectures/pluto.htm
userLTK
<orbit><orbital-mechanics><pluto>
How much are Neptune's and Uranus' orbits perturbed by Pluto and other KBOs?
userLTK
# How much are Neptune's and Uranus' orbits perturbed by Pluto and other KBOs?

(Asked by: username_0 on 2018-02-19)

Reading another question, I came across the argument that inconsistencies in Neptune's and Uranus' orbits lead to the discovery of Pluto. [This brief write-up](http://pluto.jhuapl.edu/Participate/learn/What-We-Know.php?link=Discovery-of-Pluto) mentions Percival Lowell and William H. Pickering by name as two people who looked for the theoretical 9th planet.

My question is, were inconsistencies in Neptune's and Uranus' orbits detectable by early 20th century methods or were these scientists just chasing calculation or estimation errors with dreams of finding the next planet. My (guess) is that Pluto is much too small, and too far away and just one of many similar mass kuiperbelt objects, so it's unlikely that it was really discovered by measured inconsistency in Uranus/Neptune orbits method, (despite the fact that [there are articles that say that's precisely how Pluto was discovered](http://coolcosmos.ipac.caltech.edu/ask/154-Who-discovered-Pluto-)).

In a nutshell, that's the question. Was the wobble that Pluto's causes on Neptune's orbit observable by 1910-1930 observation methods. And related, was the wobble that the entire kuiperbelt (some 20 to 50 times the mass of little pluto, but much more spread out), was that wobble detectible by 1910-1930 methods.

Hard math isn't necessary to me for an answer, as I find the math hard to follow sometimes, so feel free to answer with or without mathematical calculations.

**Tags:** orbit, orbital-mechanics, pluto
> **Comments:**
> **username_0**: @Kozaky Good suggestion.   I found this, which says the predictions used for where to look for Pluto were basically bogus.   (LOL).   http://ircamera.as.arizona.edu/NatSci102/NatSci102/lectures/pluto.htm  

---

## 1 answers

### Answer by username_1 on 2018-02-23. Score: 4 | Accepted answer

Since (1) the mass of the Pluto/Charon system is very small compared with Neptune, and (2) their orbits are in 2:3 resonance, so the perturbation of Neptune's orbit would have been undetectable. University of Rochester has a good [explanation](http://www.pas.rochester.edu/~blackman/ast104/perturbations.html) of this.

> The Accidental Discovery of Pluto
>
> Later supposed perturbations of the orbits of Uranus and Neptune suggested
> the presence of yet another planet beyond the orbit of Neptune.
> Eventually, in 1930, a new planet Pluto was discovered, but we now
> know that the calculations in this case were also in error because of
> an incorrect assumption about the mass of the new planet. It is now
> believed that the supposed deviations in the orbits of Neptune and
> Uranus were errors in measurement because the actual properties of
> Pluto would not have accounted for the supposed perturbations. Thus,
> the discovery of Pluto was a kind of accident

> **Comments:**
> **username_0**: I added the quote in case the link dies.  
> **username_2**: Because they are in resonance, some perturbation surely exists, but it affects their orbit significantly only on a much longer time. Probably the orbit of the Pluto is not an exact ellipse.  

---

