A series of US space probes. The first Pioneers, launched in 1958–9, were intended as Moon probes, but none succeeded. Pioneers 5–9, in 1960–8, were put into orbit around the Sun, monitoring solar activity and conditions in interplanetary space. Pioneers 10 and 11, the last and best-known of the series, were the first probes to reach Jupiter, photographing the planet and studying its environment. Pioneer 10, launched in 1972 March, flew past Jupiter in 1973 December. Pioneer 11, launched 1973 April passed Jupiter in 1974 December and then became the first probe to reach Saturn, in 1979 September. Both Pioneers are currently on their way out of the Solar System. Pioneer 10 crossed the orbit of Pluto in 1983 June, the first spacecraft to do so. Contact with it was finally lost in 2003 January at a distance of 82 AU. Contact with Pioneer 11 was lost in 1995 November.
http://nssdc.gsfc.nasa.gov/nmc/spacecraftDisplay.do?id=1972-012A NASA information page for Pioneer 10.
http://nssdc.gsfc.nasa.gov/nmc/spacecraftDisplay.do?id=1973-019A NASA information page for Pioneer 11.
Subjects: Astronomy and Astrophysics.