Triton (moon) discovery; he later successfully suggested the name Hyperion, previously chosen by John Herschel, for the eighth moon of Saturn when he discovered it. Triton is unique among all large moons in the Solar System for its retrograde orbit around its planet (i.e. it orbits in a direction opposite to the planet's rotation). Most of the outer irregular moons of Jupiter and Saturn also have retrograde orbits, as do some of Uranus's outer moons. However, these moons are all much more distant from their primaries, and are small in comparison; the largest of them (Phoebe) has only 8% of the diameter
Discovery and exploration of the Solar System Soviet "Lunokhod 1", which landed on the Moon in 1970. The first to visit another planet was Sojourner, which travelled 500 metres across the surface of Mars in 1997. The only manned rover to visit another world was NASA's Lunar rover, which traveled with Apollos 15, 16 and 17 between 1971 and 1972. Overview of some missions to the Solar System. See also the categories for missions to , , , and . Crewed exploration of the Solar System ended in 1972. The first human being to reach space (defined as an altitude of over 100 km) and to orbit