Voyager

The Voyager program sent two identical spacecraft to tour the outer solar system, taking advantage of a rare alignment of Jupiter, Saturn, Uranus and Neptune that allowed one spacecraft to swing from planet to planet using each one’s gravity. Voyager 2 launched on August 20, 1977, and Voyager 1 followed on September 5 on a faster path. Both were built and are operated by NASA’s Jet Propulsion Laboratory.

Between them, they transformed our view of the giant planets: active volcanoes on Jupiter’s moon Io, the structure of Saturn’s rings, and the only close-up views ever taken of Uranus and Neptune, both visited by Voyager 2. In 1990, Voyager 1 turned back to take the “Pale Blue Dot” image of Earth from about 6 billion kilometers away. Each spacecraft also carries a Golden Record of sounds and images from Earth, a message for anyone who might find it.

Voyager 1 crossed into interstellar space in 2012, and Voyager 2 followed in 2018. Nearly 50 years after launch, both are still sending data home, though their power is slowly running out and engineers have been switching off instruments one by one to keep them going as long as possible.