Celestial mechanics

, Volume 43, Issue 1–4, pp 55–68 | Cite as

Planet X — The current status

  • P. K. Seidelmann
  • R. S. Harrington
Long Term Evolution of Planetary Systems Session on Planetary Dynamics


Neptune and Pluto were discovered because of predictions derived from the differences between the observations and ephemerides of Uranus, but Pluto wasn't the predicted planet and the discrepancies still exist. This continuing existence of systematic differences between the observations and ephemerides of Uranus and Neptune has led to predictions of a Planet X. The demise of the dinosaurs and the existence of comets have been cited as additional evidence for another celestial object.

Therefore, possible bodies have been hypothesized in the outer part of the solar system, or out beyond the solar system, including a binary companion, Nemesis. The theory of relativity and the incompleteness of the law of gravity have also been suggested as explanations for the outer planet discrepancies. Predictions of the possible locations of planet X have been made, with rather large uncertainties, and selected searches of some regions have yielded nothing. IRAS and Pioneer observations exist as additional sources of useful observational data.


Observational Data Solar System Systematic Difference Additional Source Large Uncertainty 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.


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Copyright information

© Kluwer Academic Publishers 1988

Authors and Affiliations

  • P. K. Seidelmann
    • 1
  • R. S. Harrington
    • 1
  1. 1.U. S. Naval ObservatoryUSA

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