Moons of Uranus irregular moons have been identified using ground-based telescopes. Two more small inner moons, Cupid and Mab, were discovered using the Hubble Space Telescope in 2003. As of 2016, the moon Margaret was the last Uranian moon discovered, and its characteristics were published in October 2003. After Herschel discovered Titania and Oberon on January 11, 1787, he subsequently believed that he had observed four other moons: two on January 18 and February 9, 1790, and two more on February 28 and March 26, 1794. It was thus believed for many decades thereafter that Uranus had a system of six satellites, though
Moons of Uranus the four latter moons were never confirmed by any other astronomer. Lassell's observations of 1851, in which he discovered Ariel and Umbriel, however, failed to support Herschel's observations; Ariel and Umbriel, which Herschel certainly ought to have seen if he had seen any satellites beside Titania and Oberon, did not correspond to any of Herschel's four additional satellites in orbital characteristics. Herschel's four spurious satellites were thought to have sidereal periods of 5.89 days (interior to Titania), 10.96 days (between Titania and Oberon), 38.08 days, and 107.69 days (exterior to Oberon). It was therefore concluded that Herschel's four satellites were