The Voyager program launched two probes, Voyager 1 and 2, in 1977 to study Jupiter, Saturn, Uranus, and Neptune. During their "Grand Tour" of the outer planets, the probes discovered many details about the planets and their moons, such as volcanoes on Jupiter's moon Io. After completing their primary mission in 1989, the Voyagers continue their journey into interstellar space, having sent back over a trillion bits of scientific data. They carry a "Golden Record" containing sounds and images selected to portray the diversity of life and culture on Earth to any intelligent extraterrestrial entities who may find them.