Jupiter

The first man-made objects to travel to Jupiter were Pioneer 10 in December 1973 and Pioneer 11 in December 1974. These were very simple spacecraft, which provided preliminary information about the Jovian system. They made measurements of the radiation belts, the magnetic field, and obtained rather crude images of the planet and its satellites.

The more detailed measurements were made by the two Voyager spacecraft, which passed by Jupiter in March and July, 1979. These very capable spacecraft included a large array of scientific instruments to measure properties of the planet and its environment. Although it is the photographs taken by the Voyagers which are most widely known, much more information was acquired. Ultraviolet and infrared spectra, charged particle counts, and magnetic field measurements were also obtained, in order to provide a more complete view of the entire Jovian system. Since the encounters were separated by several months, information obtained from Voyager 1 was used in the planning of the Voyager 2 observations, in order to maximize the scientific return. Similarly, the results of Pioneer and ground-based measurements were used to plan the Voyager observations. Thus the observations of the future build on the measurements of the past.

In 1989, the Galileo spacecraft was launched, with objective of orbiting and studying Jupiter. The mission suffered many setbacks, however, including a malfunction that prevented the main antenna from deploying. Nonetheless, NASA scientists were able to reprogram Galileo's software remotely, allowing the probe to meet approximately 70% of mission objectives. In late 1995, the spacecraft reached Jupiter, settling into orbit to study the planet and its satellites at close range. Galileo also released a probe carrying six instruments into the Jovian atmosphere to make direct measurements of the planet's composition. Galileo has had a remarkable record of success while functioning in the Jovian system from 1995-2002. Many thousands of photographs of Jupiter and its moons have been returned along with much additional data. Galileo has been instrumental in helping find over 20 new moons of Jupiter.