Voyager

Photo montage of the gas giants from the Voyager ‘grand tour’. Bottom to top, with increasing distance from the inner Solar System, are Jupiter, Saturn, Uranus, and Neptune.

Either of two US space probes. Voyager 1, launched on 5 September 1977, passed the planet Jupiter in March 1979, and reached Saturn in November 1980. Voyager 2 was launched earlier, on 20 August 1977, on a slower trajectory that took it past Jupiter in July 1979, Saturn in August 1981, Uranus in January 1986, and Neptune in August 1989. Like the Pioneer probes, the Voyagers are now far beyond the orbit of Pluto.

Their tasks include helping scientists to locate the heliopause, the boundary at which the influence of the Sun gives way to the forces exerted by other stars. Voyager 1 is expected to reach this point between 2013 and 2015, Voyager 2 some five years later.

Both Voyagers carry coded recordings called ‘Sounds of Earth’, intended to inform any other civilizations that might find them.

Voyager 2 was not intended to visit Uranus and Neptune, but scientists were able to reprogram its computer to take it past those planets. Voyager 2 passed by Neptune at an altitude of 4,800 km/3,000 mi; its radio signals took 4 hours 6 minutes to reach Earth.