Which NASA mission became the first to visit all four giant planets?

Voyager 2 became the first NASA mission to visit all four giant planets: Jupiter, Saturn, Uranus, and Neptune.

Launched on August 20, 1977, Voyager 2 used a rare alignment of the outer planets to gain speed through gravity-assist flybys. It encountered Jupiter in 1979, Saturn in 1981, Uranus in 1986, and Neptune in 1989.

The spacecraft returned landmark observations, including evidence of active geology on several moons, new details about Uranus’s atmosphere and rings, and the first close views of Neptune. Voyager 1 followed a different trajectory after Saturn and did not visit Uranus or Neptune.

Voyager 2 is often confused with Voyager 1 because both spacecraft later entered interstellar space. Voyager 2, however, remains unique among spacecraft for visiting every planet in the Solar System’s giant-planet group.