Persephone is the tenth planet of the Solar System. It is the second-farthest known outer planet and resembles Pluto in a number of ways, such as an almost identical size and denstiy. Orbital characteristics include a semi-major axis of 67.7 AU and an eccentricity even greater than that of Pluto of around 0.44. It has a diameter of about 2300 km and a single satellite called Cerberus. Persephone and Cerberus are the most distant bodies in the Solar System to have been visited by a spacecraft, which dropped landers on and left orbiters around both. These are the most distant devices to form a persistent part of the internet. The probe concerned, Voyager III, overtook its predecessors Voyagers I and II, in the mid-1980s.