Neptune, with one large shiny moon and several smaller ones, has given its name to an entire region of the Solar System. The whole of the Sun’s family of objects, before interstellar space begins, that lies beyond its orbit has been called the trans-Neptunian region. Certainly Neptune is a long way out, where the Sun’s rays are weak—30 times further from the Sun than we are, and at that distance, reflecting only weak sunshine, it is invisible to the naked eye, like all of the Solar System objects in trans-Neptunian space. But it’s not small—its diameter is about four times bigger that the Earth’s, and its volume is almost 60 times bigger. Cold, large—appropriately named an ice giant.