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 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).

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.

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    $\begingroup$ I vaguely remember reading a Patrick Moore book that said the inaccuracies in Neptune's orbital calculations were later found to be mathematical errors and Pluto's position was coincidental. Could be wrong. Worth digging out that old book now! $\endgroup$ – user10106 Feb 19 '18 at 10:20
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    $\begingroup$ @Kozaky Good suggestion. I found this, which says the predictions used for where to look for Pluto were basically bogus. (LOL). ircamera.as.arizona.edu/NatSci102/NatSci102/lectures/pluto.htm $\endgroup$ – userLTK Feb 19 '18 at 11:59

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 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

  • $\begingroup$ I added the quote in case the link dies. $\endgroup$ – userLTK Feb 23 '18 at 12:38

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