Claim: Pluto has gravity.

Following the discovery of the planet Neptune in 1846 , there was considerable speculation that another planet might exist beyond its orbit . The search began in the mid-19th century and culminated at the start of the 20th with Percival Lowell 's quest for Planet X. Lowell proposed the Planet X hypothesis to explain apparent discrepancies in the orbits of the giant planets , particularly Uranus and Neptune , speculating that the gravity of a large unseen ninth planet could have perturbed Uranus enough to account for the irregularities .   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 reclassified Pluto and its largest neighbours as dwarf planets , leaving Neptune the farthest known planet in the Solar System .   While the astronomical community widely agrees that Planet X , as originally envisioned , does not exist , the concept of an as-yet-unobserved planet has been revived by a number of astronomers to explain other anomalies observed in the outer Solar System . As of March 2014 , observations with the WISE telescope have ruled out the possibility of a Saturn-sized object -LRB- 95 Earth mass -RRB- out to 10,000 AU , and a Jupiter-sized -LRB- ~ 318 Earth mass -RRB- or larger object out to 26,000 AU .   In 2014 , based on similarities of the orbits of a group of recently discovered extreme trans-Neptunian objects , astronomers hypothesized the existence of a super-Earth planet , 2 to 15 times the mass of the Earth and beyond 200 AU with possibly a high inclined orbit at some 1500 AU . In 2016 further work showed this unknown distant planet is likely on an inclined , eccentric orbit that goes no closer than about 200 AU and no further than about 1600 AU from the Sun . The orbit is predicted to be anti-aligned to the clustered extreme trans-Neptunian objects .  Because Pluto is no longer considered a planet by the International Astronomical Union , this new hypothetical object has become known as Planet Nine .