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
Planet Nine perihelia also reached values where the objects would not be observed, requiring a population of Sednas significantly larger than current estimates. They then, after declining, fell to values low enough for the objects to enter planet-crossing orbits leading to their ejection from the Solar System, requiring an initial population inconsistent with current models of the early Solar System to explain current observations. Based on these challenges Shankman et al. concluded that the existence of Planet Nine is unlikely and that the currently observed alignment of the existing TNOs is a temporary phenomenon that will disappear as more objects are detected.