Lieder drew the name Planet X from the hypothetical planet once searched for by astronomers to account for discrepancies in the orbits of Uranus and Neptune. In 1894, Bostonian astronomer Percival Lowell became convinced that the planets Uranus and Neptune had slight discrepancies in their orbits. He concluded that they were being tugged by the gravity of another, more distant planet, which he called "Planet X". However, nearly a century of searching failed to turn up any evidence for such an object (Pluto was initially believed to be Planet X, but was later determined to be too small).