Percival Lowell proposed the Planet X hypothesis to explain apparent discrepancies in the orbits of the giant planets, particularly Uranus and Neptune. 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 planet, 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.
About Planets beyond Neptune in brief
Percival Lowell proposed the Planet X hypothesis to explain apparent discrepancies in the orbits of the giant planets, particularly Uranus and Neptune. 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 planet, 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. 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 out to 10,000 AU, and a Jupiter-sized or larger object out to 26,000AU. 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 farther than about 1,200 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 IAU, this new hypothetical object has become known as Planet Nine.
In 1846, the French mathematician Urbain Le Verrier used Newtonian mechanics to analyse perturbations in the orbit of Uranus, and hypothesised that they were caused by the gravitational pull of a yet-undiscovered planet. He predicted the position of this new planet and sent his calculations to German astronomer Johann Gottfried Galle. The night following his receipt of the letter, Galle and his student Heinrich d’Arrest discovered Neptune. Even before Neptune’s discovery, some speculated that one planet alone was not enough to explain the discrepancy. In 1850, James Ferguson claimed that it must be a new planet, which he named Hyperion. Jacques Babinet claimed that another planet of roughly 12 Earth masses must exist beyond Neptune. He postulated that two planets lay beyond Uranus. In 1863, the British amateur astronomer the Reverend Thomas John Hussey reported a conversation he had had with French astronomer Alexis Bouvard to George Biddell Airy. Hussey had suggested to Bouvard that the unusual motion of UranUS might be due to the gravitational influence of an undiscovered planet, and Bouvard replied that the idea had occurred to him, and that he had corresponded with Peter Andreas Hansen, director of the Seeberg Observatory in Gotha, about the subject. The British Astronomer Royal said he had observed a star, GR17kk, which was a new star. He claimed it was a star he had lost at the United States Naval Observatory.
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This page is based on the article Planets beyond Neptune published in Wikipedia (as of Dec. 06, 2020) and was automatically summarized using artificial intelligence.
