Learn the outermost planet in the solar system.
Pluto is not always the outermost planet in the solar system. Discovered in 1930 by American astronomer Clyde Tombaugh (1906-1997), was thought to be the smallest planet in the solar system until 2006, when it was reclassified as a dwarf planet.
It is composed of rock and ice, with methane ice on the surface and a thin methane atmosphere. Pluto's very eccentric orbit carried it inside Neptunes orbit on January 23, 1979. It remained there until March 15, 1999. During that time, Neptune was thought to be the outermost planet in the solar system. Pluto is one of many dwarf planets in orbit.