Neptune was discovered on September 23, 1846, as the result of lengthy mathematical work by John Couch Adams and Jean Urbain Le Verrier (1811-1877). Only one week later talk surfaced of yet a more distant planet. Astronomers realized the Sun's gravity was capable of holding a planet at a distance of at least four times the distance of Neptune. In addition, Simon Newcomb (1835-1909) of the U.S. Naval Observatory announced in 1846 that Neptune's mass was not sufficient to account for the disturbances of the orbit of Uranus.

Apparently, Uranus was being affected by Neptune and a yet more distant planet, but much work remained before the search could begin. The orbit of Neptune had to be carefully determined to see if its path was being influenced by any planet besides its nearby neighbors Jupiter, Saturn, and Uranus.

Another astronomer added an additional hint as to the existence of a...