(The following information is from "NASA, The First 25 Years, 1958-1983," NASA, U.S. Government Printing Office, Washington, D.C., 1983, p. 98.)
Pioneer 10 (Pioneer Jupiter), March 3, 1972, Jupiter encounter, December 3, 1973.
First spacecraft to leave the solar system, 5:00 a.m. PDT, June 13,1983. Carries plaque with an easily-interpreted message: a drawing of a woman and a man, a diagram of the solar system, and a map locating the solar system with reference to some galactic pulsars.
Basic mission was the first flyby of Jupiter. In addition, was the first flight beyond Mars and first crossing of the asteroid belt; first close-up pictures of Jupiter's Great Red Spot and atmosphere; and first crossings of orbits of Uranus, Pluto, and Neptune.
Discoveries: (1) the heliosphere (Sun's atmosphere) extends much farther than previously thought and appears to "breathe" in and out once every 11-year cycle; (2) Jupiter is a liquid planet; (3) first model of Jupiter's huge magnetosphere; (4) first accurate measurements of mass and densities of Jupiter's planet-sized moons; (5) proof of origin of the gegenschein and zodiacal light.
Pioneer 11 (Pioneer Saturn), April 6, 1973, Jupiter encounter, December 2, 1974.
Carries plaque identical to Pioneer 10. Passed within 42,760 km (26,725 mi) of the planet's cloud tops, taking the only existing pictures of its polar regions. Jupiter's gravitational field was used to swing it back across the solar system to Saturn.
Saturn encounter, September 1,1979, Renamed Pioneer Saturn after Jupiter encounter. 565 new discoveries came from its path through the ring plane (2,000 km (1,200 mi) below them) and within 21,400 km (13,300 mi) of the cloud tops.
Results: the planet has a magnetic field, magnetosphere, and radiation belts; its core is about twice the size of Earth; its magnetic field is 1,000 times stronger than Earth's; it appears to have more and narrower belts and zones than Jupiter; identified two new rings and found an 11th moon; measurements of Titan discouraged evidence for possibility of life. The data was useful for planning encounters of Voyagers 1 and 2.
Pioneer Venus 1, May 20, 1978, Reached Venus, December 4, 1978.
Orbiter mission to observe Venus for one complete rotation on its axis; globally surveyed its atmosphere and environment, studied its topography, calculated its shape and density.
Results: (1) first full-disc picture of Venus shows a turbulent, cloudy atmosphere, bright cloud areas wrapped about both polar regions, and a Y feature covering most of the central part of this disc; (2) a thick, pale yellow opaque atmosphere obscures the surface, but radar scanner revealed flat rolling plains, a mountain as high as Mount Everest, great rift valleys, continent-sized highland areas, and two large volcanoes; (3) data provided measurements on high-speed winds, changing global paterns of clouds and cloud-level winds, a high-altitude haze of sulfuric acid, and a surface temperature of 482 degrees C (900 degress F).
The Orbiter's mission has been extended to 1985.
Pioneer Venus 2, August 8, 1978, Reached Venus, December 9, 1978.
A multiprobe mission made up of a bus, a large probe, and three identical small probes to measure the atmosphere top to bottom. The Bus measured the upper atmosphere and then burned up. The Probes, which descended to the surface, were not designed to survive impact, but one returned data for approximately 67 minutes.
Data showing the presence of large amounts of rare gases in the atmosphere suggest a far larger contribution by the Sun to Venus' atmosphere than to Earth's during the early evolution of the solar system.