<P> Clyde Tombaugh 's discovery of Pluto in 1930 appeared to validate Lowell 's hypothesis , and Pluto was officially named the ninth planet . In 1978 , Pluto was conclusively determined to be too small for its gravity to affect the giant planets , resulting in a brief search for a tenth planet . The search was largely abandoned in the early 1990s , when a study of measurements made by the Voyager 2 spacecraft found that the irregularities observed in Uranus 's orbit were due to a slight overestimation of Neptune 's mass . After 1992 , the discovery of numerous small icy objects with similar or even wider orbits than Pluto led to a debate over whether Pluto should remain a planet , or whether it and its neighbours should , like the asteroids , be given their own separate classification . Although a number of the larger members of this group were initially described as planets , in 2006 the International Astronomical Union ( IAU ) reclassified Pluto and its largest neighbours as dwarf planets , leaving Neptune the farthest known planet in the Solar System . </P>
<P> Clyde Tombaugh 's discovery of Pluto in 1930 appeared to validate Lowell 's hypothesis , and Pluto was officially named the ninth planet . In 1978 , Pluto was conclusively determined to be too small for its gravity to affect the giant planets , resulting in a brief search for a tenth planet . The search was largely abandoned in the early 1990s , when a study of measurements made by the Voyager 2 spacecraft found that the irregularities observed in Uranus 's orbit were due to a slight overestimation of Neptune 's mass . After 1992 , the discovery of numerous small icy objects with similar or even wider orbits than Pluto led to a debate over whether Pluto should remain a planet , or whether it and its neighbours should , like the asteroids , be given their own separate classification . Although a number of the larger members of this group were initially described as planets , in 2006 the International Astronomical Union ( IAU ) reclassified Pluto and its largest neighbours as dwarf planets , leaving Neptune the farthest known planet in the Solar System . </P>
which term is described as small icy bodies that orbit the sun just beyond neptune ​
which term is described as small icy bodies that orbit the sun just beyond neptune ​
dwarf planets
dwarf planets