n.
Supposed distant planet of the solar system , hypothesized on the basis of calculations of effects on the orbits of Uranus and Neptune.
The term was first used by Percival Lowell 0441; 1905, and though his prediction eventually resulted in the discovery of Pluto (1930), Pluto's mass was insufficient to explain the apparent perturbations of Uranus and Neptune. Proposals and searches for other planets beyond Neptune or Pluto continued sporadically during the remainder of the 20th century. However, Voyager spacecraft data gathered about the masses of the outer planets indicate that no additional large bodies are needed to explain the planets' observed orbits. See also Kuiper belt .