Voyager is a NASA mission. It consists of 2 spacecraft, Voyager 1 and Voyager 2. Both crafts began their mission in 1977. They are still sending data back to Earth. The goal of Voyager is to explore the outer Solar System and beyond.
The first step of their huge journey was at gas giants, Jupiter and Saturn. Voyagers 1 and 2 discovered volcanoes on Jupiter's moon, Io. They also studied Saturn's rings. After that, the crafts continued further out into the Solar System.
Voyager 1 headed to the edge of the Solar System. Here it could learn more about the space beyond our Solar System. We call this the 'interstellar medium'. However, before it set off, Voyager turned its camera around. It then took a photo of Earth from 6 billion kilometres away. In the image, the Earth looks like a tiny pale blue dot.
Voyager 1 reached interstellar space in 2012 (6 years before Voyager 2) and is still going. It has travelled further from Earth than any other spacecraft.
The Voyager mission is expected to carry on until about 2025. At this point the spacecraft will run out of power. The craft contain a kind of time capsule of Earth. If they are ever found, this golden record can be played to reveal sounds and images from Earth.