NASA - National Aeronautics and Space Administration

Voyager is either of two United States space probes launched in 1977 to Jupiter and beyond. The two crafts continue to provide valuable information.

The Voyager 2 astronomical observatory was launched in 1977 and flew past Neptune in 1989. It transmitted important information about the planet's rings, moons, and atmosphere. Image credit: World Book illustration by Oxford Illustrators Limited

Information gathered by the Voyager probes forms the basis of the modern study of Jupiter, Saturn, Uranus, Neptune, and their satellites, rings, and magnetic fields (regions where magnetic force can be detected). The probes discovered nearly two dozen natural satellites. They also found evidence of geologic activity on two previously known moons -- volcanoes on Jupiter's moon Io and icy geysers on Neptune's moon Triton. The mission also discovered numerous craters on most of the satellites, an ancient record of intense bombardment by meteoroids and comets. Scientists used Voyager data to calculate the density of 17 satellites and to determine the composition of the atmosphere of Saturn's moon Titan.

The National Aeronautics and Space Administration (NASA) launched Voyager 1 on Sept. 5, 1977. The probe made its closest approach to Jupiter on March 5, 1979, encountered Saturn on Nov. 12, 1980, then headed toward interstellar space (the space between the stars). Voyager 2, launched on Aug. 20, 1977, made its closest approach to Jupiter on July 9, 1979, Saturn on Aug. 25, 1981, Uranus on Jan. 24, 1986, and Neptune on Aug. 25, 1989, then traveled toward interstellar space.

The Voyagers carried identical sets of scientific instruments. One instrument measured the strength, shape, and direction of the planets' magnetic fields. Another studied waves traveling through plasma trapped within the fields. Plasma consists of electrically charged atoms as well as electrons that are not parts of atoms.

Three devices measured the quantities and speeds of these charged particles. Five instruments measured ultraviolet rays, visible light, infrared rays, and radio waves given off by the planets and their satellites, rings, and plasma. Also, as the two crafts moved behind each planet, the planet's atmosphere and rings blocked the radio signals transmitted by the Voyagers in ways that revealed details of their structure.

The Voyagers' radio receivers and their particle and magnetism detectors were still operating in the early 2000's. Scientists monitored their data in hope of detecting the heliopause, where interstellar space begins. Scientists suspect that the closest part of this boundary will be found about 9 billion miles (15 billion kilometers) from the sun. One Voyager almost certainly will reach the heliopause before 2015, when the crafts' radioactively powered generators run down.

Contributor: Carolyn Porco, Ph.D., Professor, Cussini Imaging Central Laboratory for Operations, Southwest Research Institute.

How to cite this article: To cite this article, World Book recommends the following format: Porco, Carolyn. "Voyager." World Book Online Reference Center. 2004. World Book, Inc. http://www.worldbookonline.com/wb/Article?id=ar588865.

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