Thirty years after the Voyager probes were launched toward

the outer planets of the solar system they continue to

send back valuable data, albeit more slowly now because of their extreme distance from Earth.

The Voyager missions provided new insight and dispelled some misconceptions about the outer planets and the moons orbiting them.


sent back photographs of a thin ring around Jupiter, eruptions of sulfur volcanoes on Jupiter’s moon Io

and geysers of liquid nitrogen on Neptune’s moon Triton, and revealed an icy crust possibly hiding an ocean on Jupiter’s moon Europa. Voyager 2 revealed that Neptune – far from being the gentle blue planet researchers had known –

has the most

violent winds in the solar system at 2,100 kilometers per hour.

Now, having entered the heliosphere where solar wind begins to dissipate into thinner interstellar gas, Voyager 1 is the most distant man-made object from Earth. It has traveled 15.5 billion kilometers from the sun. Voyager 2, now 12.5 billion kilometers from the sun, could enter the heliosphere by the end of the year.

“It’s a testament to Voyager’s designers, builders and operators that both spacecraft continue to deliver important findings more than 25 years after their primary mission to Jupiter and Saturn concluded,” Alan Stern, associate administrator for NASA’s Science Mission Directorate

said in an Aug. 20

press release.

The probes have inspired numerous science fiction books, movies and television shows, including the 1979 film “Star Trek: The Motion Picture” in which the

fictitious Voyager 6 returns to Earth as a sentient being called V’ger.

The serendipitous alignment of the solar system’s gas giants –



Uranus and Neptune –

in the late 1970s provided

a series of gravity assists for both spacecraft. But such an alignment only occurs every 176 years. The Voyager mission was born to take advantage of this rare occurrence.

Originally called the Grand Tour mission, two probes were planned for launch between 1976 and 1977 to Jupiter, Saturn and Pluto; another two probes were to be launched in 1979 to Jupiter, Uranus and Neptune.

To fulfill its plan, NASA began developing the technologically advanced Thermoelectric Outer Planets Spacecraft, but the space agency was hit by budget constraints that saw the program severely scaled back in 1972.

The scaling down of the mission,

which slashed cost projections by a third, reduced the technology of the probes to little more than an updated version of what was used on the Mariner missions of the 1960s.

Both Voyager spacecraft were equipped with five scientific instruments designed to study solar wind, magnetic fields, energetic particles and radio waves. Since they would spend too much time away from the sun to use solar power they were outfitted with radioisotope thermoelectric generators, which produce less than 300

watts of power.

The number of probes was reduced to two and their primary mission was to provide information about Jupiter and Saturn, as well as their respective moons. The opportunity to scout Uranus and Neptune, however, presented a dilemma since the probes would not be able to perform a close flyby of Saturn’s moon Titan.

Therefore, the two probes were slated for two separate trajectories, one that would allow for a close Titan flyby and another that would allow for flybys of Uranus and Neptune.

Voyager 1 was launched for the close Titan flyby while Voyager 2 was launched toward Uranus and Neptune.

Because of its

trajectory, Voyager 2 was launched first on Aug. 20, 1977. Voyager 1 launched Sep. 5, 1977. Voyager 1 overtook Voyager 2 in the asteroid belt between Mars and Jupiter. Voyager 1 arrived at Jupiter in March

1979, while Voyager 2 reached the giant planet four months later. Voyager 2 arrived at Uranus in January

1986 and Neptune in August


NASA’s Deep Space Network still is used to communicate with the Voyager spacecraft.