Moons of Uranus and so would be considered (dwarf) planets if they were in direct orbit about the Sun. The remaining moons were discovered after 1985, either during the "Voyager 2" flyby mission or with the aid of advanced Earth-based telescopes. The first two moons to be discovered were Titania and Oberon, which were spotted by Sir William Herschel on January 11, 1787, six years after he had discovered the planet itself. Later, Herschel thought he had discovered up to six moons (see below) and perhaps even a ring. For nearly 50 years, Herschel's instrument was the only one with which the moons
Double planet that this definition of double planet depends on the pair's distance from the Sun. If the Earth–Moon system happened to orbit farther away from the Sun than it does now, then Earth would win the tug of war. For example, at the orbit of Mars, the Moon's tug-of-war value would be 1.05. Also, several tiny moons discovered since Asimov's proposal would qualify as double planets by this argument. Neptune's small outer moons Neso and Psamathe, for example, have tug-of-war values of 0.42 and 0.44, less than that of Earth's Moon. Yet their masses are tiny compared to Neptune's, with an