June 13, 1983

1983: Pioneer 10, launched in 1972 to explore Jupiter, crossed the orbit of Saturn in 1976 and the orbit of Uranus in 1979. On June 13, 1983, the craft crossed the orbit of Neptune, and so became the first human-made object to leave the proximity of the major planets of the Solar System. The mission came to an official end on March 31, 1997. (Pioneer 10 on a Star-37E kick motor just prior to being encapsulated for launch, February 1972)