Neptune was found when astronimers John Couch Adams and Urbain Jean Joseph Leverrier calculated the position of a new planet which they thought was altering the orbit of Uranus. When Neptune was first observed by German astronimer Johann Gottfried Galle in 1846. Even after the discovery of Neptune the orbits of Uranus and Neptune were still diferent from what astronimers thought they should be. This led to the search for yet another planet.

The astronimers were surprised when they discovered Pluto, as they were expecting a planet much larger than the earth. But Pluto is only 3000km in diameter, smaller than what was previously thought to be the smallest planet in our solar system, Mercury. With the discovery of Pluto, both Uranus and Neptune are following their predicted path.