Discovery and exploration of the Solar System Domenico Cassini later discovered four more moons of Saturn and the Cassini division in Saturn's rings. Edmond Halley realised in 1705 that repeated sightings of a comet were recording the same object, returning regularly once every 75–76 years. This was the first evidence that anything other than the planets orbited the Sun. Around this time (1704), the term "Solar System" first appeared in English. In 1781, William Herschel was looking for binary stars in the constellation of Taurus when he observed what he thought was a new comet. Its orbit revealed that it was a new planet, Uranus, the first
Moons of Neptune orbit Neptune at an average of 125 times the distance between Earth and the Moon. Neptune has the largest Hill sphere in the Solar System, owing primarily to its large distance from the Sun; this allows it to retain control of such distant moons. Nevertheless, Jupiter's S/2003 J 2 orbits at the greatest percentage of the primary's Hill radius of all the moons in the Solar System on average, and the Jovian moons in the Carme and Pasiphae groups orbit at a greater percentage of their primary's Hill radius than Psamathe and Neso. The mass distribution of the Neptunian moons