In pictures: Farthest man-made spacecraft's 40-year journey
NASA's Voyager mission launched two spacecraft in 1977 to take advantage of a favourable alignment of Jupiter, Saturn, Uranus, and Neptune. Voyager 1 is the first-ever manmade object to leave the solar system and enter interstellar space whereas Voyager 2 was the first to image all four outer planets and is still the only spacecraft to visit Uranus and Neptune.