Voyager 2

Voyager 2 launched on August 20, 1977 — sixteen days before its twin — on a trajectory exploiting a planetary alignment that occurs once every 176 years. It remains the only spacecraft to have visited all four giant planets, returning humanity’s only close-up images of Uranus in 1986 and Neptune in 1989, where it discovered the Great Dark Spot and geysers on the moon Triton.

The ‘Grand Tour’ revealed volcanoes on Io, the ice shell of Europa, the braided rings of Saturn, and ten new moons of Uranus. Voyager 2 crossed into interstellar space in 2018 and, like its twin, carries the Golden Record — sounds and images of Earth curated as a message to whoever, or whatever, may find it in the far future.