The beginning of Solar System exploration by space probes in the 1960s spurred a renewed interest in planetary science. A split in definitions regarding satellites occurred around then: planetary scientists began to reconsider the large moons as also being planets, but astronomers who were not planetary scientists generally did not. (This is not exactly the same as the definition used in the previous century, which classed all satellites as secondary planets, even non-round ones like Saturn's Hyperion or Mars's Phobos and Deimos.) All the eight major planets and their planetary-mass moons have since been explored by spacecraft, as have many asteroids and the dwarf planets Ceres and Pluto; however, so far the only planetary-mass body beyond Earth that has been explored by humans is the Moon.