Planet X — The current status

@article{Seidelmann1987PlanetX,
  title={Planet X — The current status},
  author={P. Seidelmann and Robert S. Harrington},
  journal={Celestial mechanics},
  year={1987},
  volume={43},
  pages={55-68}
}
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… 
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