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. Early speculation In the 1840s, 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. Le Verrier predicted the position of this new planet and sent his calculations to German astronomer Johann Gottfried Galle. On 23 September 1846, the night following his receipt of the letter, Galle and his student Heinrich d'Arrest discovered Neptune, exactly where Le Verrier had predicted. There remained some slight discrepancies in the giant planets' orbits. These were taken to indicate the existence of yet another planet orbiting beyond Neptune. Even before Neptune's discovery, some speculated that one planet alone was not enough to explain the discrepancy. On 17 November 1834, the British amateur astronomer the Reverend Thomas John Hussey reported a conversation he had had with French astronomer Alexis Bouvard to George Biddell Airy, the British Astronomer Royal. Hussey reported that when he suggested to Bouvard that the unusual motion of Uranus might be due to the gravitational influence of an undiscovered planet, 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. Hansen's opinion was that a single body could not adequately explain the motion of Uranus, and postulated that two planets lay beyond Uranus. In 1848, Jacques Babinet raised an objection to Le Verrier's calculations, claiming that Neptune's observed mass was smaller and its orbit larger than Le Verrier had initially predicted. He postulated, based largely on simple subtraction from Le Verrier's calculations, that another planet of roughly 12 Earth masses, which he named "Hyperion", must exist beyond Neptune. Le Verrier denounced Babinet's hypothesis, saying, "[There is] absolutely nothing by which one could determine the position of another planet, barring hypotheses in which imagination played too large a part." In 1850 James Ferguson, Assistant Astronomer at the United States Naval Observatory, noted that he had "lost" a star he had observed, GR1719k, which Lt. Matthew Maury, the superintendent of the Observatory, claimed was evidence that